Terje Koren Berntsen

• Karset, Inger Helene H.; Berntsen, Terje Koren; Storelvmo, Trude; Alterskjær, Kari; Grini, Alf; Oliviè, Dirk Jan Leo; Kirkevåg, Alf; Seland, Øyvind; Iversen, Trond & Schulz, Michael (2018). Strong impacts on aerosol indirect effects from historical oxidant changes. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  18(10), s 7669- 7690 . doi: 10.5194/acp-18-7669-2018
• Skeie, Ragnhild Bieltvedt; Berntsen, Terje Koren; Aldrin, Magne Tommy; Holden, Marit & Myhre, Gunnar (2018). Climate sensitivity estimates - Sensitivity to radiative forcing time series and observational data. Earth System Dynamics.  ISSN 2190-4979.  9(2), s 879- 894 . doi: 10.5194/esd-9-879-2018
• Tanaka, Katsumasa; Lund, Marianne Tronstad; Aamaas, Borgar & Berntsen, Terje Koren (2018). Climate effects of non-compliant Volkswagen diesel cars. Environmental Research Letters.  ISSN 1748-9326.  13(4) . doi: 10.1088/1748-9326/aab18c
• Aamaas, Borgar; Berntsen, Terje Koren; Fuglestvedt, Jan S.; Shine, Keith P & Collins, William J (2017). Regional temperature change potentials for short-lived climate forcers based on radiative forcing from multiple models. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  17(17), s 10795- 10809 . doi: 10.5194/acp-17-10795-2017 Fulltekst i vitenarkiv.
• Aas, Kjetil Schanke; Gisnås, Kjersti; Westermann, Sebastian & Berntsen, Terje Koren (2017). A Tiling Approach to Represent Subgrid Snow Variability in Coupled Land Surface–Atmosphere Models. Journal of Hydrometeorology.  ISSN 1525-755X.  18(1), s 49- 63 . doi: 10.1175/JHM-D-16-0026.1 Fulltekst i vitenarkiv.
• Lund, Marianne Tronstad; Aamaas, Borgar; Berntsen, Terje Koren; Bock, Lisa; Burkhardt, Ulrike; Fuglestvedt, Jan S. & Shine, Keith P (2017). Emission metrics for quantifying regional climate impacts of aviation. Earth System Dynamics.  ISSN 2190-4979.  8(3), s 547- 563 . doi: 10.5194/esd-8-547-2017 Fulltekst i vitenarkiv.
• Lund, Marianne Tronstad; Berntsen, Terje Koren & Samset, Bjørn Hallvard (2017). Sensitivity of black carbon concentrations and climate impact to aging and scavenging in OsloCTM2-M7. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  17(9), s 6003- 6022 . doi: 10.5194/acp-17-6003-2017 Fulltekst i vitenarkiv. Vis sammendrag

  Accurate representation of black carbon (BC) concentrations in climate models is a key prerequisite for understanding its net climate impact. BC aging and scavenging are treated very differently in current models. Here, we examine the sensitivity of three-dimensional (3-D), temporally resolved BC concentrations to perturbations to individual model processes in the chemistry transport model OsloCTM2–M7. The main goals are to identify processes related to aerosol aging and scavenging where additional observational constraints may most effectively improve model performance, in particular for BC vertical profiles, and to give an indication of how model uncertainties in the BC life cycle propagate into uncertainties in climate impacts. Coupling OsloCTM2 with the microphysical aerosol module M7 allows us to investigate aging processes in more detail than possible with a simpler bulk parameterization. Here we include, for the first time in this model, a treatment of condensation of nitric acid on BC. Using kernels, we also estimate the range of radiative forcing and global surface temperature responses that may result from perturbations to key tunable parameters in the model. We find that BC concentrations in OsloCTM2–M7 are particularly sensitive to convective scavenging and the inclusion of condensation by nitric acid. The largest changes are found at higher altitudes around the Equator and at low altitudes over the Arctic. Convective scavenging of hydrophobic BC, and the amount of sulfate required for BC aging, are found to be key parameters, potentially reducing bias against HIAPER Pole-to-Pole Observations (HIPPO) flight-based measurements by 60 to 90  %. Even for extensive tuning, however, the total impact on global-mean surface temperature is estimated to less than 0.04 K. Similar results are found when nitric acid is allowed to condense on the BC aerosols. We conclude, in line with previous studies, that a shorter atmospheric BC lifetime broadly improves the comparison with measurements over the Pacific. However, we also find that the model–measurement discrepancies can not be uniquely attributed to uncertainties in a single process or parameter. Model development therefore needs to be focused on improvements to individual processes, supported by a broad range of observational and experimental data, rather than tuning of individual, effective parameters such as the global BC lifetime.

• Sand, Maria; Samset, Bjørn Hallvard; Balkanski, Yves; Bauer, Susanne; Bellouin, Nicolas; Berntsen, Terje Koren; Bian, Huisheng; Chin, Mian; Diehl, Thomas; Easter, Richard; Ghan, Steve J.; Iversen, Trond; Kirkevåg, Alf; Lamarque, Jean-Francois; Lin, Guangxing; Liu, Xiaohong; Luo, Gan; Myhre, Gunnar; Van Noije, Twan P.C.; Penner, Joyce E.; Schulz, Michael; Seland, Øyvind; Skeie, Ragnhild Bieltvedt; Stier, Philip; Takemura, Toshihiko; Tsigaridis, Kostas; Yu, Fangqun; Zhang, Kai & Zhang, Hua (2017). Aerosols at the poles: an AeroCom Phase II multi-model evaluation. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  17(19), s 12197- 12218 . doi: 10.5194/acp-17-12197-2017 Fulltekst i vitenarkiv.
• Skeie, Ragnhild Bieltvedt; Fuglestvedt, Jan S.; Berntsen, Terje Koren; Peters, Glen Philip; Andrew, Robbie; Allen, Myles & Kallbekken, Steffen (2017). Perspective has a strong effect on the calculation of historical contributions to global warming. Environmental Research Letters.  ISSN 1748-9326.  12(2) . doi: 10.1088/1748-9326/aa5b0a Vis sammendrag

  The politically contentious issue of calculating countries' contributions to climate change is strongly dependent on methodological choices. Different principles can be applied for distributing efforts for reducing human-induced global warming. According to the 'Brazilian Proposal', industrialized countries would reduce emissions proportional to their historical contributions to warming. This proposal was based on the assumption that the political process would lead to a global top-down agreement. The Paris Agreement changed the role of historical responsibilities. Whereas the agreement refers to equity principles, differentiation of mitigation efforts is delegated to each country, as countries will submit new national contributions every five years without any international negotiation. It is likely that considerations of historical contributions and distributive fairness will continue to play a key role, but increasingly so in a national setting. Contributions to warming can be used as a background for negotiations to inform and justify positions, and may also be useful for countries' own assessment of what constitutes reasonable and fair contributions to limiting warming. Despite the fact that the decision from COP21 explicitly rules out compensation in the context of loss and damage, it is likely that considerations of historical responsibility will also play a role in future discussions. However, methodological choices have substantial impacts on calculated contributions to warming, including rank-ordering of contributions, and thus support the view that there is no single correct answer to the question of how much each country has contributed. There are fundamental value-related and ethical questions that cannot be answered through a single set of calculated contributions. Thus, analyses of historical contributions should not present just one set of results, but rather present a spectrum of results showing how the calculated contributions vary with a broad set of choices. Our results clearly expose some of the core issues related to climate responsibility.

• Aamaas, Borgar; Berntsen, Terje Koren; Fuglestvedt, Jan S.; Shine, Keith P & Bellouin, Nicolas (2016). Regional emission metrics for short-lived climate forcers from multiple models. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  16(11), s 7451- 7468 . doi: 10.5194/acp-16-7451-2016 Vis sammendrag

  For short-lived climate forcers (SLCFs), the impact of emissions depends on where and when the emissions take place. Comprehensive new calculations of various emission metrics for SLCFs are presented based on radiative forcing (RF) values calculated in four different (chemical-transport or coupled chemistry–climate) models. We distinguish between emissions during summer (May–October) and winter (November–April) for emissions in Europe and East Asia, as well as from the global shipping sector and global emissions. The species included in this study are aerosols and aerosol precursors (BC, OC, SO2, NH3), as well as ozone precursors (NOx, CO, VOCs), which also influence aerosols to a lesser degree. Emission metrics for global climate responses of these emissions, as well as for CH4, have been calculated using global warming potential (GWP) and global temperature change potential (GTP), based on dedicated RF simulations by four global models. The emission metrics include indirect cloud effects of aerosols and the semi-direct forcing for BC. In addition to the standard emission metrics for pulse and sustained emissions, we have also calculated a new emission metric designed for an emission profile consisting of a ramping period of 15 years followed by sustained emissions, which is more appropriate for a gradual implementation of mitigation policies. For the aerosols, the emission metric values are larger in magnitude for emissions in Europe than East Asia and for summer than winter. A variation is also observed for the ozone precursors, with largest values for emissions in East Asia and winter for CO and in Europe and summer for VOCs. In general, the variations between the emission metrics derived from different models are larger than the variations between regions and seasons, but the regional and seasonal variations for the best estimate also hold for most of the models individually. Further, the estimated climate impact of an illustrative mitigation policy package is robust even when accounting for the fact that the magnitude of emission metrics for different species in a given model is correlated. For the ramping emission metrics, the values are generally larger than for pulse or sustained emissions, which holds for all SLCFs. For SLCFs mitigation policies, the dependency of metric values on the region and season of emission should be considered.

• Aas, Kjetil Schanke; Dunse, Thorben; Collier, E.; Schuler, Thomas; Berntsen, Terje Koren; Kohler, Jack & Luks, Bartlomiej (2016). The climatic mass balance of Svalbard glaciers: A 10-year simulation with a coupled atmosphere-glacier mass balance model. The Cryosphere.  ISSN 1994-0416.  10(3), s 1089- 1104 . doi: 10.5194/tc-10-1089-2016 Fulltekst i vitenarkiv.
• Koffi, Brigitte; Schulz, Michael; Bréon, François-Marie; Dentener, Frank; Steensen, Birthe Marie Rødssæteren; Griesfeller, Jan; Winker, David; Balkanski, Yves; Bauer, Susanne E.; Bellouin, Nicolas; Berntsen, Terje Koren; Bian, Huisheng; Chin, Mian; Diehl, Thomas; Easter, Richard; Ghan, Steven; Hauglustaine, Didier A.; Iversen, Trond; Kirkevåg, Alf; Liu, Xiaohong; Lohmann, Ulrike; Myhre, Gunnar; Rasch, Phil; Seland, Øyvind; Skeie, Ragnhild Bieltvedt; Steenrod, Stephen D.; Stier, Philip; Tackett, Jason; Takemura, Toshihiko; Tsigaridis, Kostas; Vuolo, Maria Raffaella; Yoon, Jinho & Zhang, Kai (2016). Evaluation of the aerosol vertical distribution in global aerosol models through comparison against CALIOP measurements: AeroCom phase II results. Journal of Geophysical Research - Atmospheres.  ISSN 2169-897X.  121(12), s 7254- 7283 . doi: 10.1002/2015JD024639 Vis sammendrag

  The ability of 11 models in simulating the aerosol vertical distribution from regional to global scales, as part of the second phase of the AeroCom model intercomparison initiative (AeroCom II), is assessed and compared to results of the first phase. The evaluation is performed using a global monthly gridded data set of aerosol extinction profiles built for this purpose from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) Layer Product 3.01. Results over 12 subcontinental regions show that five models improved, whereas three degraded in reproducing the interregional variability in Zα0–6 km, the mean extinction height diagnostic, as computed from the CALIOP aerosol profiles over the 0–6 km altitude range for each studied region and season. While the models' performance remains highly variable, the simulation of the timing of the Zα0–6 km peak season has also improved for all but two models from AeroCom Phase I to Phase II. The biases in Zα0–6 km are smaller in all regions except Central Atlantic, East Asia, and North and South Africa. Most of the models now underestimate Zα0–6 km over land, notably in the dust and biomass burning regions in Asia and Africa. At global scale, the AeroCom II models better reproduce the Zα0–6 km latitudinal variability over ocean than over land. Hypotheses for the performance and evolution of the individual models and for the intermodel diversity are discussed. We also provide an analysis of the CALIOP limitations and uncertainties contributing to the differences between the simulations and observations.

• Aas, Kjetil Schanke; Berntsen, Terje Koren; Boike, Julia; Etzelmuller, Bernd; Kristjansson, Jon Egill; Maturilli, Marion; Schuler, Thomas; Stordal, Frode & Westermann, Sebastian (2015). A comparison between simulated and observed surface energy balance at the Svalbard Archipelago. Journal of Applied Meteorology and Climatology.  ISSN 1558-8424.  54(5), s 1102- 1119 . doi: 10.1175/JAMC-D-14-0080.1
• Aas, Kjetil Schanke; Dunse, Thorben; Collier, E.; Schuler, Thomas; Berntsen, Terje Koren; Kohler, Jack & Luks, B. (2015). Simulating the climatic mass balance of Svalbard glaciers from 2003 to 2013 with a high-resolution coupled atmosphere-glacier model. The Cryosphere Discussions.  ISSN 1994-0432.  9, s 5775- 5815 . doi: 10.5194/tcd-9-5775-2015 Fulltekst i vitenarkiv.
• Eckhardt, Sabine; Quennehen, B.; Oliviè, Dirk Jan Leo; Berntsen, Terje Koren; Cherian, Regimon; Christensen, J.; Collins, W.; Crepinsek, S; Daskalakis, N; Flanner, M; Herber, Andreas; Heyes, C; Hodnebrog, Øivind; Huang, Lan; Kanakidou, M; Klimont, Z; Langner, J.; Law, Katharine S.; Lund, Marianne Tronstad; Mahmood, R; Massling, A; Myriokefalitakis, S; Nielsen, Izabela Ewa; Nøjgaard, J.K.; Quaas, Johannes; Quinn, Patricia K.; Raut, Jean-Christophe; Rumbold, Steven T.; Schulz, Michael; Sharma, S; Skeie, Ragnhild Bieltvedt; Skov, Henrik; Uttal, T; von Salzen, Knut & Stohl, Andreas (2015). Current model capabilities for simulating black carbon and sulfate concentrations in the Arctic atmosphere: A multi-model evaluation using a comprehensive measurement data set. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  15(16), s 9413- 9433 . doi: 10.5194/acp-15-9413-2015 Fulltekst i vitenarkiv. Vis sammendrag

  The concentrations of sulfate, black carbon (BC) and other aerosols in the Arctic are characterized by high values in late winter and spring (so-called Arctic Haze) and low values in summer. Models have long been struggling to capture this seasonality and especially the high concentrations associated with Arctic Haze. In this study, we evaluate sulfate and BC concentrations from eleven different models driven with the same emission inventory against a comprehensive pan-Arctic measurement data set over a time period of two years (2008–2009). The set of models consisted of one Lagrangian particle dispersion model, four chemistry-transport models (CTMs), one atmospheric chemistry-weather forecast model and five chemistry-climate models (CCMs), of which two were nudged to meteorological analyses and three were running freely. The measurement data set consisted of surface measurements of equivalent BC (eBC) from five stations (Alert, Barrow, Pallas, Tiksi and Zeppelin), elemental carbon (EC) from Station Nord and Alert and aircraft measurements of refractory BC (rBC) from six different campaigns. We find that the models generally captured the measured eBC/rBC and sulfate concentrations quite well, compared to past comparisons. However, the aerosol seasonality at the surface is still too weak in most models. Concentrations of eBC and sulfate averaged over three surface sites are underestimated in winter/spring in all but one model (model means for January-March underestimated by 59 and 37% for BC and sulfate, respectively), whereas concentrations in summer are overestimated in the model mean (by 88 and 44% for July–September), but with over- as well as underestimates present in individual models. The most pronounced eBC underestimates, not included in the above multi-site average, are found for the station Tiksi in Siberia where the measured annual mean eBC concentration is three times higher than the average annual mean for all other stations. This suggests an underestimate of BC sources in Russia in the emission inventory used. Based on the campaign data, biomass burning was identified as another cause of the modelling problems. For sulfate, very large differences were found in the model ensemble, with an apparent anti-correlation between modeled surface concentrations and total atmospheric columns. There is a strong correlation between observed sulfate and eBC concentrations with consistent sulfate/eBC slopes found for all Arctic stations, indicating that the sources contributing to sulfate and BC are similar throughout the Arctic and that the aerosols are internally mixed and undergo similar removal. However, only three models reproduced this finding, whereas sulfate and BC are weakly correlated in the other models. Overall, no class of models (e.g., CTMs, CCMs) performed better than the others and differences are independent of model resolution.

• Pedersen, Christina Alsvik; Gallet, J.-C.; Ström, J.; Gerland, S; Hudson, S.R.; Forsström, S.; Isaksson, E. & Berntsen, Terje Koren (2015). In situ observations of black carbon in snow and the corresponding spectral surface albedo reduction. Journal of Geophysical Research - Biogeosciences.  ISSN 2169-8953.  120(4), s 1476- 1489 . doi: 10.1002/2014JD022407
• Sand, Maria; Berntsen, Terje Koren; Salzen, K. von; Flanner, Mark G.; Langner, Joakim & Victor, David G. (2015). Response of Arctic temperature to changes in emissions of short-lived climate forcers. Nature Climate Change.  ISSN 1758-678X. . doi: 10.1038/nclimate2880 Vis sammendrag

  There is growing scientific and political interest in the impacts of climate change and anthropogenic emissions on the Arctic. Over recent decades temperatures in the Arctic have increased at twice the global rate, largely as a result of ice–albedo and temperature feedbacks. Although deep cuts in global CO2 emissions are required to slow this warming, there is also growing interest in the potential for reducing short-lived climate forcers (SLCFs; refs 9,10). Politically, action on SLCFs may be particularly promising because the benefits of mitigation are seen more quickly than for mitigation of CO2 and there are large co-benefits in terms of improved air quality11. This Letter is one of the first to systematically quantify the Arctic climate impact of regional SLCFs emissions, taking into account black carbon (BC), sulphur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds (VOCs), organic carbon (OC) and tropospheric ozone (O3), and their transport processes and transformations in the atmosphere. This study extends the scope of previous works by including more detailed calculations of Arctic radiative forcing and quantifying the Arctic temperature response. We find that the largest Arctic warming source is from emissions within the Asian nations owing to the large absolute amount of emissions. However, the Arctic is most sensitive, per unit mass emitted, to SLCFs emissions from a small number of activities within the Arctic nations themselves. A stringent, but technically feasible mitigation scenario for SLCFs, phased in from 2015 to 2030, could cut warming by 0.2 (±0.17) K in 2050.

• Stohl, Andreas; Aamaas, Borgar; Amann, M; Baker, LH; Bellouin, N; Berntsen, Terje Koren; Boucher, O; Cherian, R; Collins, W; Daskalakis, N; Dusinska, Maria; Eckhardt, Sabine; Fuglestvedt, Jan S.; Harju, Mikael; Heyes, C; Hodnebrog, Øivind; Hao, J; Im, U; Kanakidou, M; Klimont, Z; Kupiainen, K; Law, KS; Lund, Marianne Tronstad; Maas, R; MacIntosh, CR; Myhre, Gunnar; Myriokefalitakis, S; Oliviè, Dirk Jan Leo; Quaas, J; Quennehen, B; Raut, JC; Rumbold, ST; Samset, Bjørn Hallvard; Schulz, M; Seland, Øyvind; Shine, KP; Skeie, Ragnhild Bieltvedt; Wang, S; Yttri, Karl Espen & Zhu, T (2015). Evaluating the climate and air quality impacts of short-lived pollutants. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  15(18), s 10529- 10566 . doi: 10.5194/acp-15-10529-2015 Fulltekst i vitenarkiv. Vis sammendrag

  This paper presents a summary of the work done within the European Union's Seventh Framework Programme project ECLIPSE (Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants). ECLIPSE had a unique systematic concept for designing a realistic and effective mitigation scenario for short-lived climate pollutants (SLCPs; methane, aerosols and ozone, and their precursor species) and quantifying its climate and air quality impacts, and this paper presents the results in the context of this overarching strategy. The first step in ECLIPSE was to create a new emission inventory based on current legislation (CLE) for the recent past and until 2050. Substantial progress compared to previous work was made by including previously unaccounted types of sources such as flaring of gas associated with oil production, and wick lamps. These emission data were used for present-day reference simulations with four advanced Earth system models (ESMs) and six chemistry transport models (CTMs). The model simulations were compared with a variety of ground-based and satellite observational data sets from Asia, Europe and the Arctic. It was found that the models still underestimate the measured seasonality of aerosols in the Arctic but to a lesser extent than in previous studies. Problems likely related to the emissions were identified for northern Russia and India, in particular. To estimate the climate impacts of SLCPs, ECLIPSE followed two paths of research: the first path calculated radiative forcing (RF) values for a large matrix of SLCP species emissions, for different seasons and regions independently. Based on these RF calculations, the Global Temperature change Potential metric for a time horizon of 20 years (GTP20) was calculated for each SLCP emission type. This climate metric was then used in an integrated assessment model to identify all emission mitigation measures with a beneficial air quality and short-term (20-year) climate impact. These measures together defined a SLCP mitigation (MIT) scenario. Compared to CLE, the MIT scenario would reduce global methane (CH4) and black carbon (BC) emissions by about 50 and 80%, respectively. For CH4, measures on shale gas production, waste management and coal mines were most important. For non-CH4 SLCPs, elimination of high-emitting vehicles and wick lamps, as well as reducing emissions from gas flaring, coal and biomass stoves, agricultural waste, solvents and diesel engines were most important. These measures lead to large reductions in calculated surface concentrations of ozone and particulate matter. We estimate that in the EU, the loss of statistical life expectancy due to air pollution was 7.5 months in 2010, which will be reduced to 5.2 months by 2030 in the CLE scenario. The MIT scenario would reduce this value by another 0.9 to 4.3 months. Substantially larger reductions due to the mitigation are found for China (1.8 months) and India (11–12 months). The climate metrics cannot fully quantify the climate response. Therefore, a second research path was taken. Transient climate ensemble simulations with the four ESMs were run for the CLE and MIT scenarios, to determine the climate impacts of the mitigation. In these simulations, the CLE scenario resulted in a surface temperature increase of 0.70 ± 0.14 K between the years 2006 and 2050. For the decade 2041–2050, the warming was reduced by 0.22 ± 0.07 K in the MIT scenario, and this result was in almost exact agreement with the response calculated based on the emission metrics (reduced warming of 0.22±0.09K). The metrics calculations suggest that non-CH4 SLCPs contribute ~ 22% to this response and CH4 78%. This could not be fully confirmed by the transient simulations, which attributed about 90% of the temperature response to CH4 reductions. Attribution of the observed temperature response to non-CH4 SLCP emission reductions and BC specifically is hampered in the transient simulations by small forcing and co-emitted spec

• Samset, Bjørn Hallvard; Myhre, Gunnar; Herber, Andreas; Kondo, Yutaka; Li, Shao-Meng; Moteki, Nobuhiro; Koike, Makoto; Oshima, Naga; Schwarz, Joshua P.; Balkanski, Yves; Bauer, Susanne E.; Bellouin, Nicolas; Berntsen, Terje Koren; Bian, Huisheng; Chin, Mian; Diehl, Thomas; Easter, Richard C.; Ghan, Steven John; Iversen, Trond; Kirkevåg, Alf; Lamarque, Jean-François; Lin, Guangxing; Liu, Xiaohong; Penner, Joyce E.; Schulz, Michael; Seland, Øyvind; Skeie, Ragnhild Bieltvedt; Stier, Philip; Takemura, Toshihiko; Tsigaridis, Kostas & Zhang, Kai (2014). Modelled black carbon radiative forcing and atmospheric lifetime in AeroCom Phase II constrained by aircraft observations. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  14(22), s 12465- 12477 . doi: 10.5194/acp-14-12465-2014 Vis sammendrag

  Atmospheric black carbon (BC) absorbs solar radiation, and exacerbates global warming through exerting positive radiative forcing (RF). However, the contribution of BC to ongoing changes in global climate is under debate. Anthropogenic BC emissions, and the resulting distribution of BC concentration, are highly uncertain. In particular, long-range transport and processes affecting BC atmospheric lifetime are poorly understood. Here we discuss whether recent assessments may have overestimated present-day BC radiative forcing in remote regions. We compare vertical profiles of BC concentration from four recent aircraft measurement campaigns to simulations by 13 aerosol models participating in the AeroCom Phase II intercomparison. An atmospheric lifetime of BC of less than 5 days is shown to be essential for reproducing observations in remote ocean regions, in line with other recent studies. Adjusting model results to measurements in remote regions, and at high altitudes, leads to a 25% reduction in AeroCom Phase II median direct BC forcing, from fossil fuel and biofuel burning, over the industrial era. The sensitivity of modelled forcing to BC vertical profile and lifetime highlights an urgent need for further flight campaigns, close to sources and in remote regions, to provide improved quantification of BC effects for use in climate policy

• Tsigaridis, K; Daskalakis, N; Kanakidou, M; Adams, Peter J.; Artaxo, Paulo; Bahadur, R; Balkanski, Yves; Bauer, S. E.; Bellouin, Nicolas; Benedetti, Anna; Bergman, Tommi; Berntsen, Terje Koren; Beukes, J. P.; Bian, H; Carslaw, K; Chin, Mian; Curci, G; Diehl, Thomas; Easter, Richard C.; Ghan, Steven John; Gong, SL; Hodzic, A; Hoyle, CR; Iversen, Trond; Jathar, S; Jimenez, J. L.; Kaiser, Johannes W.; Kirkevåg, Alf; Koch, D; Kokkola, Harri; Lee, Y.H.; Lin, G; Liu, X; Luo, G; Ma, X; Mann, Graham W.; Mihalopoulos, N; Morcrette, J.J; Muller, JF; Myhre, Gunnar; Myriokefalitakis, S; Ng, NL; O'Donnell, D; Penner, J.E.; Pozzoli, L; Pringle, Kirsty J.; Russell, LM; Schulz, M; Sciare, J.; Seland, Øyvind; Shindell, Drew T.; Sillman, Sanford; Skeie, Ragnhild Bieltvedt; Spracklen, D; Stavrakou, T; Steenrod, S; Takemura, Toshihiko; Tiitta, P; Tilmes, S; Tost, Holger; Van Noije, T; van Zyl, P. G.; von Salzen, Knut; Yu, F.; Wang, Z; Wang, Z.; Zaveri, Rahul A.; Zhang, H; Zhang, K; Zhang, Q & Zhang, X (2014). The AeroCom evaluation and intercomparison of organic aerosol in global models. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  14(19), s 10845- 10895 . doi: 10.5194/acp-14-10845-2014 Vis sammendrag

  This paper evaluates the current status of global modeling of the organic aerosol (OA) in the troposphere and analyzes the differences between models as well as between models and observations. Thirty-one global chemistry transport models (CTMs) and general circulation models (GCMs) have participated in this intercomparison, in the framework of AeroCom phase II. The simulation of OA varies greatly between models in terms of the magnitude of primary emissions, secondary OA (SOA) formation, the number of OA species used (2 to 62), the complexity of OA parameterizations (gas-particle partitioning, chemical aging, multiphase chemistry, aerosol microphysics), and the OA physical, chemical and optical properties. The diversity of the global OA simulation results has increased since earlier AeroCom experiments, mainly due to the increasing complexity of the SOA parameterization in models, and the implementation of new, highly uncertain, OA sources. Diversity of over one order of magnitude exists in the modeled vertical distribution of OA concentrations that deserves a dedicated future study. Furthermore, although the OA / OC ratio depends on OA sources and atmospheric processing, and is important for model evaluation against OA and OC observations, it is resolved only by a few global models

• Fuglestvedt, Jan S.; Dalsøren, Stig Bjørløw; Samset, Bjørn Hallvard; Berntsen, Terje Koren; Myhre, Gunnar; Hodnebrog, Øivind; Eide, Magnus Strandmyr & Bergh, Trond Flisnes (2014). Climate penalty for shifting shipping to the Arctic. Environmental Science and Technology.  ISSN 0013-936X.  48(22), s 13273- 13279 . doi: 10.1021/es502379d Vis sammendrag

  The changing climate in the Arctic opens new shipping routes. A shift to shorter Arctic transit will, however, incur a climate penalty over the first one and a half centuries. We investigate the net climate effect of diverting a segment of Europe–Asia container traffic from the Suez to an Arctic transit route. We find an initial net warming for the first one-and-a-half centuries, which gradually declines and transitions to net cooling as the effects of CO2 reductions become dominant, resulting in climate mitigation only in the long term. Thus, the possibilities for shifting shipping to the Arctic confront policymakers with the question of how to weigh a century-scale warming with large uncertainties versus a long-term climate benefit from CO2 reductions.

• Grewe, Volker; Frömming, Christine; Matthes, Sigrun; Brinkop, Sabine; Ponater, Michael; Dietmüller, Simone; Jöckel, Patrick; Garny, Hella; Tsati, Eleni; Dahlmann, Katrin; Søvde, Ole Amund; Fuglestvedt, Jan S.; Berntsen, Terje Koren; Shine, Keith P.; Irvine, Emma A.; Champougny, Thierry & Hullah, Peter (2014). Aircraft routing with minimal climate impact: The REACT4C climate cost function modelling approach (V1.0). Geoscientific Model Development.  ISSN 1991-959X.  7(1), s 175- 201 . doi: 10.5194/gmd-7-175-2014 Vis sammendrag

  In addition to CO2, the climate impact of aviation is strongly influenced by non-CO2 emissions, such as nitrogen oxides, influencing ozone and methane, and water vapour, which can lead to the formation of persistent contrails in ice-supersaturated regions. Because these non-CO2 emission effects are characterised by a short lifetime, their climate impact largely depends on emission location and time; that is to say, emissions in certain locations (or times) can lead to a greater climate impact (even on the global average) than the same emission in other locations (or times). Avoiding these climate-sensitive regions might thus be beneficial to climate. Here, we describe a modelling chain for investigating this climate impact mitigation option. This modelling chain forms a multi-step modelling approach, starting with the simulation of the fate of emissions released at a certain location and time (time-region grid points). This is performed with the chemistry–climate model EMAC, extended via the two submodels AIRTRAC (V1.0) and CONTRAIL (V1.0), which describe the contribution of emissions to the composition of the atmosphere and to contrail formation, respectively. The impact of emissions from the large number of time-region grid points is efficiently calculated by applying a Lagrangian scheme. EMAC also includes the calculation of radiative impacts, which are, in a second step, the input to climate metric formulas describing the global climate impact of the emission at each time-region grid point. The result of the modelling chain comprises a four-dimensional data set in space and time, which we call climate cost functions and which describes the global climate impact of an emission at each grid point and each point in time. In a third step, these climate cost functions are used in an air traffic simulator (SAAM) coupled to an emission tool (AEM) to optimise aircraft trajectories for the North Atlantic region. Here, we describe the details of this new modelling approach and show some example results. A number of sensitivity analyses are performed to motivate the settings of individual parameters. A stepwise sanity check of the results of the modelling chain is undertaken to demonstrate the plausibility of the climate cost functions.

• Isaksen, Ivar S A; Berntsen, Terje Koren; Dalsøren, Stig Bjørløw; Eleftheratos, K.; Orsolini, Yvan; Rognerud, Bjørg; Stordal, Frode; Søvde, Ole Amund; Zerefos, C & Holmes, Chris D. (2014). Atmospheric Ozone and Methane in a Changing Climate. Atmosphere.  ISSN 2073-4433.  5(3), s 518- 535 . doi: 10.3390/atmos5030518 Fulltekst i vitenarkiv. Vis sammendrag

  Ozone and methane are chemically active climate-forcing agents affected by climate–chemistry interactions in the atmosphere. Key chemical reactions and processes affecting ozone and methane are presented. It is shown that climate-chemistry interactions have a significant impact on the two compounds. Ozone, which is a secondary compound in the atmosphere, produced and broken down mainly in the troposphere and stratosphre through chemical reactions involving atomic oxygen (O), NOx compounds (NO, NO2), CO, hydrogen radicals (OH, HO2), volatile organic compounds (VOC) and chlorine (Cl, ClO) and bromine (Br, BrO). Ozone is broken down through changes in the atmospheric distribution of the afore mentioned compounds. Methane is a primary compound emitted from different sources (wetlands, rice production, livestock, mining, oil and gas production and landfills).Methane is broken down by the hydroxyl radical (OH). OH is significantly affected by methane emissions, defined by the feedback factor, currently estimated to be in the range 1.3 to 1.5, and increasing with increasing methane emission. Ozone and methane changes are affected by NOx emissions. While ozone in general increase with increases in NOx emission, methane is reduced, due to increases in OH. Several processes where current and future changes have implications for climate-chemistry interactions are identified. It is also shown that climatic changes through dynamic processes could have significant impact on the atmospheric chemical distribution of ozone and methane, as we can see through the impact of Quasi Biennial Oscillation (QBO). Modeling studies indicate that increases in ozone could be more pronounced toward the end of this century. Thawing permafrost could lead to important positive feedbacks in the climate system. Large amounts of organic material are stored in the upper layers of the permafrost in the yedoma deposits in Siberia, where 2 to 5% of the deposits could be organic material. During thawing of permafrost, parts of the organic material that is deposited could be converted to methane. Furthermore, methane stored in deposits under shallow waters in the Arctic have the potential to be released in a future warmer climate with enhanced climate impact on methane, ozone and stratospheric water vapor. Studies performed by several groups show that the transport sectors have the potential for significant impacts on climate-chemistry interactions. There are large uncertainties connected to ozone and methane changes from the transport sector, and to methane release and climate impact during permafrost thawing.

• Jiao, C; Flanner, M; Balkanski, Y; Bauer, S.; Bellouin, N; Berntsen, Terje Koren; Bian, H; Carslaw, K; Chin, M; De Luca, N; Diehl, T; Ghan, S; Iversen, T; Kirkevag, A; Koch, D; Liu, X; Mann, G; Penner, J; Pitari, G; Schulz, M; Seland, O; Skeie, Ragnhild Bieltvedt; Steenrod, S; Stier, P; Takemura, T; Tsigaridis, K; Van Noije, T; Yun, Y & Zhang, K (2014). An aerocom assessment of black carbon in Arctic snow and sea ice. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  14(5), s 2399- 2417 . doi: 10.5194/acp-14-2399-2014 Vis sammendrag

  Though many global aerosols models prognose surface deposition, only a few models have been used to directly simulate the radiative effect from black carbon (BC) deposition to snow and sea ice. Here, we apply aerosol deposition fields from 25 models contributing to two phases of the Aerosol Comparisons between Observations and Models (AeroCom) project to simulate and evaluate within-snow BC concentrations and radiative effect in the Arctic. We accomplish this by driving the offline land and sea ice components of the Community Earth System Model with different deposition fields and meteorological conditions from 2004 to 2009, during which an extensive field campaign of BC measurements in Arctic snow occurred. We find that models generally underestimate BC concentrations in snow in northern Russia and Norway, while overestimating BC amounts elsewhere in the Arctic. Although simulated BC distributions in snow are poorly correlated with measurements, mean values are reasonable. The multi-model mean (range) bias in BC concentrations, sampled over the same grid cells, snow depths, and months of measurements, are −4.4 (−13.2 to +10.7) ng g−1 for an earlier phase of AeroCom models (phase I), and +4.1 (−13.0 to +21.4) ng g−1 for a more recent phase of AeroCom models (phase II), compared to the observational mean of 19.2 ng g−1. Factors determining model BC concentrations in Arctic snow include Arctic BC emissions, transport of extra-Arctic aerosols, precipitation, deposition efficiency of aerosols within the Arctic, and meltwater removal of particles in snow. Sensitivity studies show that the model–measurement evaluation is only weakly affected by meltwater scavenging efficiency because most measurements were conducted in non-melting snow. The Arctic (60–90° N) atmospheric residence time for BC in phase II models ranges from 3.7 to 23.2 days, implying large inter-model variation in local BC deposition efficiency. Combined with the fact that most Arctic BC deposition originates from extra-Arctic emissions, these results suggest that aerosol removal processes are a leading source of variation in model performance. The multi-model mean (full range) of Arctic radiative effect from BC in snow is 0.15 (0.07–0.25) W m−2 and 0.18 (0.06–0.28) W m−2 in phase I and phase II models, respectively. After correcting for model biases relative to observed BC concentrations in different regions of the Arctic, we obtain a multi-model mean Arctic radiative effect of 0.17 W m−2 for the combined AeroCom ensembles. Finally, there is a high correlation between modeled BC concentrations sampled over the observational sites and the Arctic as a whole, indicating that the field campaign provided a reasonable sample of the Arctic.

• Lund, Marianne Tronstad; Berntsen, Terje Koren & Fuglestvedt, Jan S. (2014). Climate impacts of short-lived climate forcers versus CO2 from biodiesel: A case of the EU on-road sector. Environmental Science and Technology.  ISSN 0013-936X.  48(24), s 14445- 14454 . doi: 10.1021/es505308g Fulltekst i vitenarkiv. Vis sammendrag

  Biofuels are proposed to play an important role in several mitigation strategies to meet future CO2 emission targets for the transport sector but remain controversial due to significant uncertainties in net impacts on environment, society, and climate. A switch to biofuels can also affect short-lived climate forcers (SLCFs), which provide significant contributions to the net climate impact of transportation. We quantify the radiative forcing (RF) and global-mean temperature response over time to EU on-road fossil diesel SLCFs and the impact of 20% (B20) and 100% (B100) replacement of fossil diesel by biodiesel. SLCFs are compared to impacts of on-road CO2 using different approaches from existing literature to account for biodiesel CO2. Given the best estimates for changes in emissions when replacing fossil diesel with biodiesel, the net positive RF from EU on-road fossil diesel SLCFs of 3.4 mW/m2 is reduced by 15% and 80% in B20 and B100, respectively. Over time the warming of SLCFs is likely small compared to biodiesel CO2 impacts. However, SLCFs may be relatively more important for the total warming than in the fossil fuel case if biodiesel from feedstock with very short rotation periods and low land-use-change impacts replaces a high fraction of fossil diesel.

• Lund, Marianne Tronstad; Berntsen, Terje Koren; Heyes, Chris; Klimont, Zbigniew & Samset, Bjørn Hallvard (2014). Global and regional climate impacts of black carbon and co-emitted species from the on-road diesel sector. Atmospheric Environment.  ISSN 1352-2310.  98, s 50- 58 . doi: 10.1016/j.atmosenv.2014.08.033 Vis sammendrag

  Diesel vehicles are a significant source of black carbon (BC) and ozone precursors, which are important contributors to climate warming, degrade air quality and harm human health. Reducing diesel emissions could mitigate near-term climate change with significant co-benefits. This study quantifies the global and regional climate impacts of BC and co-emitted short-lived climate forcers (SLCFs) from present-day on-road diesel vehicles, as well as future impacts following a current legislation emission scenario. Atmospheric concentrations are calculated by the chemical transport model OsloCTM2. The following radiative forcing (RF) and equilibrium surface temperature responses are estimated. For year 2010 on-road diesel emissions we estimate a global-mean direct RF from BC of 44 m W/m2 and an equilibrium surface temperature response of 59 mK, including the impact of BC deposition on snow. Accounting for cooling and warming impacts of co-emitted SLCFs results in a net global-mean RF and warming of 28 mW/m2 and 48 mK, respectively. Using the concept of Regional Temperature change Potential (RTP), we find significant geographical differences in the responses to regional emissions. Accounting for the vertical sensitivities of the forcing/response relation amplifies these differences. In terms of individual source regions, emissions in Europe give the largest regional contribution to equilibrium warming caused by year 2010 on-road diesel BC, while Russia is most important for Arctic warming per unit emission. The largest contribution to warming caused by the year 2050 on-road diesel sector is from emissions in South Asia, followed by East Asia and the Middle East. Hence, in regions where current legislation is not sufficient to outweigh the expected growth in activity, accelerated policy implementation is important for further future mitigation.

• Skeie, Ragnhild Bieltvedt; Berntsen, Terje Koren; Aldrin, Magne Tommy; Holden, Marit & Myhre, Gunnar (2014). A lower and more constrained estimate of climate sensitivity using updated observations and detailed radiative forcing time series. Earth System Dynamics.  ISSN 2190-4979.  5(1), s 139- 175 . doi: 10.5194/esd-5-139-2014 Vis sammendrag

  Equilibrium climate sensitivity (ECS) is constrained based on observed near-surface temperature change, changes in ocean heat content (OHC) and detailed radiative forcing (RF) time series from pre-industrial times to 2010 for all main anthropogenic and natural forcing mechanism. The RF time series are linked to the observations of OHC and temperature change through an energy balance model (EBM) and a stochastic model, using a Bayesian approach to estimate the ECS and other unknown parameters from the data. For the net anthropogenic RF the posterior mean in 2010 is 2.0 Wm−2, with a 90% credible interval (C.I.) of 1.3 to 2.8 Wm−2, excluding present-day total aerosol effects (direct + indirect) stronger than −1.7 Wm−2. The posterior mean of the ECS is 1.8 °C, with 90% C.I. ranging from 0.9 to 3.2 °C, which is tighter than most previously published estimates. We find that using three OHC data sets simultaneously and data for global mean temperature and OHC up to 2010 substantially narrows the range in ECS compared to using less updated data and only one OHC data set. Using only one OHC set and data up to 2000 can produce comparable results as previously published estimates using observations in the 20th century, including the heavy tail in the probability function. The analyses show a significant contribution of internal variability on a multi-decadal scale to the global mean temperature change. If we do not explicitly account for long-term internal variability, the 90% C.I. is 40% narrower than in the main analysis and the mean ECS becomes slightly lower, which demonstrates that the uncertainty in ECS may be severely underestimated if the method is too simple. In addition to the uncertainties represented through the estimated probability density functions, there may be uncertainties due to limitations in the treatment of the temporal development in RF and structural uncertainties in the EBM.

• Williams, JE; Hodnebrog, Øivind; van, Velthoven, PFJ; Berntsen, Terje Koren; Dessens, O; Gauss, Michael; Grewe, V; Isaksen, Ivar S A; Olivie, D; Prather, MJ & Tang, Q (2014). The influence of future non-mitigated road transport emissions on regional ozone exceedences at global scale. Atmospheric Environment.  ISSN 1352-2310.  89, s 633- 641 . doi: 10.1016/j.atmosenv.2014.02.041 Vis sammendrag

  Road Transport emissions (RTE) are a significant anthropogenic global NOx source responsible for enhancing the chemical production of tropospheric ozone (O3) in the lower troposphere. Here we analyse a multi-model ensemble which adopts the realistic SRES A1B emission scenario and a “policy-failure” scenario for RTE (A1B_HIGH) for the years 2000, 2025 and 2050. Analysing the regional trends in RTE NOx estimates shows by 2025 that differences of 0.2–0.3 Tg N yr−1 occur for most of the world regions between the A1B and A1B_HIGH estimates, except for Asia where there is a larger difference of ∼1.4 Tg N yr−1. For 2050 these differences fall to ∼0.1 Tg N yr−1, with shipping emissions becoming as important as RTE. Analysing the seasonality in near-surface O3 from the multi-model ensemble monthly mean values shows a large variability in the projected changes between different regions. For Western Europe and the Eastern US although the peak O3 mixing ratios decrease by ∼10% in 2050, there is an associated degradation during wintertime due to less direct titration from nitric oxide. For regions such as Eastern China, although total anthropogenic NOx emissions are reduced from 2025 to 2050, there is no real improvement in peak O3 levels. By normalizing the seasonal ensemble means of near-surface O3 (0–500 m) with the recommended European Commission (EC) exposure limit to derive an exceedence ratio (ER), we show that ER values greater than 1.0 occur across a wide area in the Northern Hemisphere for boreal summer using the year 2000 emissions. When adopting the future A1B_HIGH estimates, the Middle East exhibits the worst regional air quality, closely followed by Asia. For these regions the area of exceedence (ER > 1.0) for 2025 is ∼40% and ∼25% of the total area of each region, respectively. Comparing simulations employing the various scenarios shows that unmitigated RTE increases the area of exceedence in the Middle East by ∼6% and, for Asia, by ∼2% of the total regional areas. For the USA the area of exceedence approximately doubles in 2025 as a result of unmitigated RTE, with the most exceedences occurring in the southern USA. The effects across the various regions implies that unmitigated RTE would have a detrimental effect on regional health for 2025, and potentially offset the benefits introduced by mitigating e.g. international shipping emissions. By 2050 the further mitigation of non-transport emissions results in much cleaner air meaning that mitigation of RTE is not critical for achieving the defined limits in many world regions.

• Bond, Tami C.; Doherty, Sarah J.; Fahey, David W.; Forster, Piers M.; Berntsen, Terje Koren; DeAngelo, Benjamin J.; Flanner, Mark G.; Ghan, Steve; Kärcher, Bernd; Koch, Dorothy; Kinne, Stefan; Kondo, Yutaka; Quinn, Patricia K.; Sarofim, Marcus C.; Schultz, Martin G.; Schulz, Michael; Venkataraman, Chandra; Zhang, Hua; Zhang, S.; Bellouin, Nicolas; Guttikunda, Sarath K.; Hopke, Philip K.; Jacobson, Mark Z.; Kaiser, Johannes W.; Klimont, Zbigniew; Lohmann, Ulrike; Schwarz, Joshua P.; Shindell, Drew; Storelvmo, Trude; Warren, Stephen G. & Zender, Charlie S. (2013). Bounding the role of black carbon in the climate system: A scientific assessment. Journal of Geophysical Research - Atmospheres.  ISSN 2169-897X.  118(11), s 5380- 5552 . doi: 10.1002/jgrd.50171
• Myhre, Gunnar; Samset, Bjørn Hallvard; Schulz, M.; Balkanski, Y.; Bauer, S.; Berntsen, Terje Koren; Bian, H.; Bellouin, N; Chin, M; Diehl, T; Easter, R. C.; Feichter, J; Ghan, SJ; Hauglustaine, D; Iversen, Trond; Kinne, S; Kirkevåg, A; Lamarque, J. F.; Lin, G; Liu, X.; Lund, Marianne Tronstad; Luo, G; Ma, X; van Noije, T; Penner, JE; Rasch, P. J.; Ruiz, A.; Seland, Ø.; Skeie, Ragnhild Bieltvedt; Stier, P; Takemura, T.; Tsigaridis, K; Wang, P.; Wang, Z; Xu, L.; Yu, H; Yu, F.; Yoon, J.-H.; Zhang, K.; Zhang, H. & Zhou, C. (2013). Radiative forcing of the direct aerosol effect from AeroCom Phase II simulations. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  13(4), s 1853- 1877 . doi: 10.5194/acp-13-1853-2013 Fulltekst i vitenarkiv. Vis sammendrag

  We report on the AeroCom Phase II direct aerosol effect (DAE) experiment where 16 detailed global aerosol models have been used to simulate the changes in the aerosol distribution over the industrial era. All 16 models have estimated the radiative forcing (RF) of the anthropogenic DAE, and have taken into account anthropogenic sulphate, black carbon (BC) and organic aerosols (OA) from fossil fuel, biofuel, and biomass burning emissions. In addition several models have simulated the DAE of anthropogenic nitrate and anthropogenic influenced secondary organic aerosols (SOA). The model simulated all-sky RF of the DAE from total anthropogenic aerosols has a range from −0.58 to −0.02Wm−2, with a mean of −0.27Wm−2 for the 16 models. Several models did not include nitrate or SOA and modifying the estimate by accounting for this with information from the other AeroCom models reduces the range and slightly strengthens the mean. Modifying the model estimates for missing aerosol components and for the time period 1750 to 2010 results in a mean RF for the DAE of −0.35Wm−2. Compared to AeroCom Phase I (Schulz et al., 2006) we find very similar spreads in both total DAE and aerosol component RF. However, the RF of the total DAE is stronger negative and RF from BC from fossil fuel and biofuel emissions are stronger positive in the present study than in the previous AeroCom study.We find a tendency for models having a strong (positive) BC RF to also have strong (negative) sulphate or OA RF. This relationship leads to smaller uncertainty in the total RF of the DAE compared to the RF of the sum of the individual aerosol components. The spread in results for the individual aerosol components is substantial, and can be divided into diversities in burden, mass extinction coefficient (MEC), and normalized RF with respect to AOD. We find that these three factors give similar contributions to the spread in results.

• Samset, Bjørn Hallvard; Myhre, Gunnar; Schulz, M.; Balkanski, Y.; Bauer, S.; Berntsen, Terje Koren; Bian, H.; Bellouin, N.; Diehl, T.; Easter, R.C.; Ghan, S.J.; Iversen, Trond; Kinne, S.; Kirkevåg, Alf; Lamarque, J.-F.; Lin, G.; Liu, X.; Penner, J.E.; Seland, Øyvind; Skeie, Ragnhild Bieltvedt; Stier, P.; Takemura, T.; Tsigaridis, K. & Zhang, K. (2013). Black carbon vertical profiles strongly affect its radiative forcing uncertainty. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  13(5), s 2423- 2434 . doi: 10.5194/acp-13-2423-2013 Fulltekst i vitenarkiv. Vis sammendrag

  The impact of black carbon (BC) aerosols on the global radiation balance is not well constrained. Here twelve global aerosol models are used to show that at least 20% of the present uncertainty in modeled BC direct radiative forcing (RF) is due to diversity in the simulated vertical profile of BC mass. Results are from phases 1 and 2 of the global aerosol model intercomparison project (AeroCom). Additionally, a significant fraction of the variability is shown to come from high altitudes, as, globally, more than 40% of the total BC RF is exerted above 5 km. BC emission regions and areas with transported BC are found to have differing characteristics. These insights into the importance of the vertical profile of BC lead us to suggest that observational studies are needed to better characterize the global distribution of BC, including in the upper troposphere.

• Borken-Kleefeld, Jens; Fuglestvedt, Jan S. & Berntsen, Terje Koren (2013). Mode, Load, And Specific Climate Impact from Passenger Trips. Environmental Science and Technology.  ISSN 0013-936X.  47(14), s 7608- 7614 . doi: 10.1021/es4003718
• Eide, Magnus Strandmyr; Dalsøren, Stig Bjørløw; Endresen, Øyvind; Samset, Bjørn Hallvard; Myhre, Gunnar; Fuglestvedt, Jan S. & Berntsen, Terje Koren (2013). Reducing CO2 from shipping - do non-CO2 effects matter?. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  13(8), s 4183- 4201 . doi: 10.5194/acp-13-4183-2013
• Forsström, S.; Isaksson, Elisabeth; Skeie, Ragnhild Bieltvedt; Ström, Johan; Pedersen, CA; Hudson, S.R.; Berntsen, Terje Koren; Lihavainen, H.; Godtliebsen, Fred & Gerland, Sebastian (2013). Elemental carbon measurements in European Arctic snow packs. Journal of Geophysical Research - Atmospheres.  ISSN 2169-897X.  118(24), s 13,614- 13,627 . doi: 10.1002/2013JD019886 Fulltekst i vitenarkiv.
• Khodayari, Arezoo; Wuebbles, Donald J.; Olsen, Seth C.; Fuglestvedt, Jan S.; Berntsen, Terje Koren; Lund, Marianne Tronstad; Waitz, Ian; Wolfe, Philip; Forster, Piers M.; Meinshausen, Malte; Lee, David S. & Lim, Ling L. (2013). Intercomparison of the capabilities of simplified climate models to project the effects of aviation CO2 on climate. Atmospheric Environment.  ISSN 1352-2310.  75, s 321- 328 . doi: 10.1016/j.atmosenv.2013.03.055
• Lee, Y.H.; Lamarque, J.-F.; Flanner, M.G.; Jiao, C.; Shindell, D.T.; Berntsen, Terje Koren; Bisiaux, M.M.; Cao, J.; Collins, W.J.; Curran, M.; Edwards, R.; Faluvegi, G.; Ghan, S.; Horowitz, L.W.; McConnell, J.R.; Ming, J.; Myhre, Gunnar; Nagashima, T.; Naik, V.; Rumbold, S.T.; Skeie, Ragnhild Bieltvedt; Sudo, K.; Takemura, T.; Thevenon, F.; Xu, B. & Yoon, J.-H. (2013). Evaluation of preindustrial to present-day black carbon and its albedo forcing from Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP). Atmospheric Chemistry and Physics.  ISSN 1680-7316.  13(5), s 2607- 2634 . doi: 10.5194/acp-13-2607-2013 Fulltekst i vitenarkiv. Vis sammendrag

  As part of the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP), we evaluate the historical black carbon (BC) aerosols simulated by 8 ACCMIP models against observations including 12 ice core records, long-term surface mass concentrations, and recent Arctic BC snowpack measurements. We also estimate BC albedo forcing by performing additional simulations using offline models with prescribed meteorology from 1996–2000. We evaluate the vertical profile of BC snow concentrations from these offline simulations using the recent BC snowpack measurements. Despite using the same BC emissions, the global BC burden differs by approximately a factor of 3 among models due to differences in aerosol removal parameterizations and simulated meteorology: 34 Gg to 103 Gg in 1850 and 82 Gg to 315 Gg in 2000. However, the global BC burden from preindustrial to present-day increases by 2.5–3 times with little variation among models, roughly matching the 2.5-fold increase in total BC emissions during the same period.We find a large divergence among models at both Northern Hemisphere (NH) and Southern Hemisphere (SH) high latitude regions for BC burden and at SH high latitude regions for deposition fluxes. The ACCMIP simulations match the observed BC surface mass concentrations well in Europe and North America except at Ispra. However, the models fail to predict the Arctic BC seasonality due to severe underestimations during winter and spring. The simulated vertically resolved BC snow concentrations are, on average, within a factor of 2–3 of the BC snowpack measurements except for Greenland and the Arctic Ocean. For the ice core evaluation, models tend to adequately capture both the observed temporal trends and the magnitudes at Greenland sites. However, models fail to predict the decreasing trend of BC depositions/ice core concentrations from the 1950s to the 1970s in most Tibetan Plateau ice cores. The distinct temporal trend at the Tibetan Plateau ice cores indicates a strong influence from Western Europe, but the modeled BC increases in that period are consistent with the emission changes in Eastern Europe, the Middle East, South and East Asia. At the Alps site, the simulated BC suggests a strong influence from Europe, which agrees with the Alps ice core observations. At Zuoqiupu on the Tibetan Plateau, models successfully simulate the higher BC concentrations observed during the non-monsoon season compared to the monsoon season but overpredict BC in both seasons. Despite a large divergence in BC deposition at two Antarctic ice core sites, some models with a BC lifetime of less than 7 days are able to capture the observed concentrations. In 2000 relative to 1850, globally and annually averaged BC surface albedo forcing from the offline simulations ranges from 0.014 to 0.019Wm−2 among the ACCMIP models. Comparing offline and online BC albedo forcings computed by some of the same models, we find that the global annual mean can vary by up to a factor of two because of different aerosol models or different BC-snow parameterizations and snow cover. The spatial distributions of the offline BC albedo forcing in 2000 show especially high BC forcing (i.e., over 0.1Wm−2) over Manchuria, Karakoram, and most of the Former USSR. Models predict the highest global annual mean BC forcing in 1980 rather than 2000, mostly driven by the high fossil fuel and biofuel emissions in the Former USSR in 1980.

• Sand, Maria; Berntsen, Terje Koren; Kay, J.E.; Lamarque, J. F.; Seland, Øyvind & Kirkevåg, Alf (2013). The Arctic response to remote and local forcing of black carbon. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  13(1), s 211- 224 . doi: 10.5194/acp-13-211-2013
• Sand, Maria; Berntsen, Terje Koren; Seland, Øyvind & Kristjansson, Jon Egill (2013). Arctic surface temperature change to emissions of black carbon within Arctic or midlatitudes. Journal of Geophysical Research - Atmospheres.  ISSN 2169-897X.  118(14), s 7788- 7798 . doi: 10.1002/jgrd.50613
• Stevenson, D.S.; Young, P.J.; Naik, V.; Lamarque, J.-F.; Shindell, D.T.; Voulgarakis, A.; Skeie, Ragnhild Bieltvedt; Dalsøren, Stig Bjørløw; Myhre, Gunnar; Berntsen, Terje Koren; Folberth, G.A.; Rumbold, S.T.; Collins, W.J.; MacKenzie, I.A.; Doherty, R.M.; Zeng, G.; van Noije, T.P.C; Strunk, A.; Bergmann, D.; Cameron-Smith, P.; Plummer, D.A.; Strode, S.A.; Horowitz, L.; Lee, Y.H.; Szopa, S.; Sudo, K.; Nagashima, T.; Josse, B.; Cionni, I.; Righi, M.; Eyring, V.; Conley, A.; Bowman, K.W.; Wild, O. & Archibald, A. (2013). Tropospheric ozone changes, radiative forcing and attribution to emissions in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP). Atmospheric Chemistry and Physics.  ISSN 1680-7316.  13(6), s 3063- 3085 . doi: 10.5194/acp-13-3063-2013 Vis sammendrag

  Ozone (O3) from 17 atmospheric chemistry models taking part in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) has been used to calculate tropospheric ozone radiative forcings (RFs). All models applied a common set of anthropogenic emissions, which are better constrained for the present-day than the past. Future anthropogenic emissions follow the four Representative Concentration Pathway (RCP) scenarios, which define a relatively narrow range of possible air pollution emissions. We calculate a value for the pre-industrial (1750) to present-day (2010) tropospheric ozone RF of 410mWm−2. The model range of pre-industrial to present-day changes in O3 produces a spread (±1 standard deviation) in RFs of ±17 %. Three different radiation schemes were used – we find differences in RFs between schemes (for the same ozone fields) of ±10 %. Applying two different tropopause definitions gives differences in RFs of ±3 %. Given additional (unquantified) uncertainties associated with emissions, climate-chemistry interactions and land-use change, we estimate an overall uncertainty of ±30% for the tropospheric ozone RF. Experiments carried out by a subset of six models attribute tropospheric ozone RF to increased emissions of methane (44±12 %), nitrogen oxides (31±9 %), carbon monoxide (15±3 %) and non-methane volatile organic compounds (9±2 %); earlier studies attributed more of the tropospheric ozone RF to methane and less to nitrogen oxides. Normalising RFs to changes in tropospheric column ozone, we find a global mean normalised RF of 42mWm−2 DU−1, a value similar to previous work. Using normalised RFs and future tropospheric column ozone projections we calculate future tropospheric ozone RFs (mWm−2; relative to 1750) for the four future scenarios (RCP2.6, RCP4.5, RCP6.0 and RCP8.5) of 350, 420, 370 and 460 (in 2030), and 200, 300, 280 and 600 (in 2100). Models show some coherent responses of ozone to climate change: decreases in the tropical lower troposphere, associated with increases in water vapour; and increases in the sub-tropical to mid-latitude upper troposphere, associated with increases in lightning and stratosphere-to-troposphere transport. Climate change has relatively small impacts on global mean tropospheric ozone RF.

• Aldrin, Magne; Holden, Marit; Guttorp, Peter; Skeie, Ragnhild Bieltvedt; Myhre, Gunnar & Berntsen, Terje Koren (2012). Bayesian estimation of climate sensitivity based on a simple climate model fitted to observations of hemispheric temperatures and global ocean heat content. Environmetrics.  ISSN 1180-4009.  23(3), s 253- 271 . doi: 10.1002/env.2140 Vis sammendrag

  Predictions of climate change are uncertain mainly because of uncertainties in the emissions of greenhouse gases and how sensitive the climate is to changes in the abundance of the atmospheric constituents. The equilibrium climate sensitivity is defined as the temperature increase because of a doubling of the CO2 concentration in the atmosphere when the climate reaches a new steady state. CO2 is only one out of the several external factors that affect the global temperature, called radiative forcing mechanisms as a collective term. In this paper, we present a model framework for estimating the climate sensitivity. The core of the model is a simple, deterministic climate model based on elementary physical laws such as energy balance. It models yearly hemispheric surface temperature and global ocean heat content as a function of historical radiative forcing. This deterministic model is combined with an empirical, stochastic model and fitted to observations on global temperature and ocean heat content, conditioned on estimates of historical radiative forcing. We use a Bayesian framework, with informative priors on a subset of the parameters and flat priors on the climate sensitivity and the remaining parameters. The model is estimated by Markov Chain Monte Carlo techniques

• Hodnebrog, Øivind; Berntsen, Terje Koren; Dessens, O.; Gauss, Michael; Grewe, V; Isaksen, Ivar S A; Koffi, B.; Myhre, Gunnar; Oliviè, Dirk Jan Leo; Prather, M; Stordal, Frode; Szopa, S; Tang, Q; van Velthoven, P & Williams, J (2012). Future impact of traffic emissions on atmospheric ozone and OH based on two scenarios. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  12(24), s 12211- 12225 . doi: 10.5194/acp-12-12211-2012 Vis sammendrag

  The future impact of traffic emissions on atmospheric ozone and OH has been investigated separately for the three sectors AIRcraft, maritime SHIPping and ROAD traffic. To reduce uncertainties we present results from an ensemble of six different atmospheric chemistry models, each simulating the atmospheric chemical composition in a possible high emission scenario (A1B), and with emissions from each transport sector reduced by 5% to estimate sensitivities. Our results are compared with optimistic future emission scenarios (B1 and B1 ACARE), presented in a companion paper, and with the recent past (year 2000). Present-day activity indicates that anthropogenic emissions so far evolve closer to A1B than the B1 scenario. As a response to expected changes in emissions, AIR and SHIP will have increased impacts on atmospheric O3 and OH in the future while the impact of ROAD traffic will decrease substantially as a result of technological improvements. In 2050, maximum aircraft-induced O3 occurs near 80° N in the UTLS region and could reach 9 ppbv in the zonal mean during summer. Emissions from ship traffic have their largest O3 impact in the maritime boundary layer with a maximum of 6 ppbv over the North Atlantic Ocean during summer in 2050. The O3 impact of road traffic emissions in the lower troposphere peaks at 3 ppbv over the Arabian Peninsula, much lower than the impact in 2000. Radiative forcing (RF) calculations show that the net effect of AIR, SHIP and ROAD combined will change from a marginal cooling of −0.44 ± 13 mW m−2 in 2000 to a relatively strong cooling of −32 ± 9.3 (B1) or −32 ± 18 mW m−2 (A1B) in 2050, when taking into account RF due to changes in O3, CH4 and CH4-induced O3. This is caused both by the enhanced negative net RF from SHIP, which will change from −19 ± 5.3 mW m−2 in 2000 to −31 ± 4.8 (B1) or −40 ± 9 mW m−2 (A1B) in 2050, and from reduced O3 warming from ROAD, which is likely to turn from a positive net RF of 12 ± 8.5 mW m−2 in 2000 to a slightly negative net RF of −3.1 ± 2.2 (B1) or −3.1 ± 3.4 (A1B) mW m−2 in the middle of this century. The negative net RF from ROAD is temporary and induced by the strong decline in ROAD emissions prior to 2050, which only affects the methane cooling term due to the longer lifetime of CH4 compared to O3. The O3 RF from AIR in 2050 is strongly dependent on scenario and ranges from 19 ± 6.8 (B1 ACARE) to 61 ± 14 mW m−2 (A1B). There is also a considerable span in the net RF from AIR in 2050, ranging from −0.54 ± 4.6 (B1 ACARE) to 12 ± 11 (A1B) mW m−2 compared to 6.6 ± 2.2 mW m−2 in 2000.

• Isaksen, Ivar S A; Zerefos, C; Wang, W-C; Balis, D.; Eleftheratos, K.; Rognerud, Bjørg; Stordal, Frode; Berntsen, Terje Koren; Lacasce, Joseph Henry; Søvde, Ole Amund; Oliviè, Dirk Jan Leo; Orsolini, Yvan; Zyrichidou, I.; Prather, M.J. & Tuinder, O. N. E. (2012). Attribution of the Arctic ozone column deficit in March 2011. Geophysical Research Letters.  ISSN 0094-8276.  39(L24810) . doi: 10.1029/2012GL053876 Vis sammendrag

  Arctic column ozone reached record low values (∼310 DU) during March of 2011, exposing Arctic ecosystems to enhanced UV-B. We identify the cause of this anomaly using the Oslo CTM2 atmospheric chemistry model driven by ECMWF meteorology to simulate Arctic ozone from 1998 through 2011. CTM2 successfully reproduces the variability in column ozone, from week to week, and from year to year, correctly identifying 2011 as an extreme anomaly over the period. By comparing parallel model simulations, one with all Arctic ozone chemistry turned off on January 1, we find that chemical ozone loss in 2011 is enhanced relative to previous years, but it accounted for only 23% of the anomaly. Weakened transport of ozone from middle latitudes, concurrent with an anomalously strong polar vortex, was the primary cause of the low ozone When the zonal winds relaxed in mid-March 2011, Arctic column ozone quickly recovered.

• Koffi, Brigitte; Schulz, Michael; Bréon, Francois-Marie; Griesfeller, Jan; Winker, David; Balkanski, Yves; Bauer, Susanne; Berntsen, Terje Koren; Chin, Mian; Collins, William D; Dentener, Frank; Diehl, Thomas; Easter, Richard; Ghan, Steven John; Ginoux, Paul; Gong, Sunling; Horowitz, Larry W; Iversen, Trond; Kirkevåg, Alf; Koch, Dorothy; Krol, Maarten; Myhre, Gunnar; Stier, Philip & Takemura, Toshihiko (2012). Application of the CALIOP layer product to evaluate the vertical distribution of aerosols estimated by global models: AeroCom phase I results. Journal of Geophysical Research - Atmospheres.  ISSN 2169-897X.  117 . doi: 10.1029/2011JD016858 Vis sammendrag

  The CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) layer product is used for a multimodel evaluation of the vertical distribution of aerosols. Annual and seasonal aerosol extinction profiles are analyzed over 13 sub-continental regions representative of industrial, dust, and biomass burning pollution, from CALIOP 2007–2009 observations and from AeroCom (Aerosol Comparisons between Observations and Models) 2000 simulations. An extinction mean height diagnostic (Zα) is defined to quantitatively assess the models' performance. It is calculated over the 0–6 km and 0–10 km altitude ranges by weighting the altitude of each 100 m altitude layer by its aerosol extinction coefficient. The mean extinction profiles derived from CALIOP layer products provide consistent regional and seasonal specificities and a low inter-annual variability. While the outputs from most models are significantly correlated with the observed Zα climatologies, some do better than others, and 2 of the 12 models perform particularly well in all seasons. Over industrial and maritime regions, most models show higher Zα than observed by CALIOP, whereas over the African and Chinese dust source regions, Zα is underestimated during Northern Hemisphere Spring and Summer. The positive model bias in Zα is mainly due to an overestimate of the extinction above 6 km. Potential CALIOP and model limitations, and methodological factors that might contribute to the differences are discussed.

• Lund, Marianne Tronstad & Berntsen, Terje Koren (2012). Parameterization of black carbon aging in the OsloCTM2 and implications for regional transport to the Arctic. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  12(15), s 6999- 7014 . doi: 10.5194/acp-12-6999-2012 Vis sammendrag

  A critical parameter for the atmospheric lifetime of black carbon (BC) aerosols, and hence for the range over which the particles can be transported, is the aging time, i.e. the time before the aerosols become available for removal by wet deposition. This study compares two different parameterizations of BC aging in the chemistry transport model OsloCTM2: (i) A bulk parameterization (BULK) where aging is represented by a constant transfer to hydrophilic mode and (ii) a microphysical module (M7) where aging occurs through particle interaction and where the particle size distribution is accounted for. We investigate the effect of including microphysics on the distribution of BC globally and in the Arctic. We also focus on the impact on estimated contributions to Arctic BC from selected emission source regions. With more detailed microphysics (M7) there are regional and seasonal variations in aging. The aging is slower during high-latitude winter, when the production of sulfate is lower, than in lower latitudes and during summer. High-latitude concentrations of BC are significantly increased during winter compared to BULK. Furthermore, M7 improves the model performance at Arctic surface stations, especially the accumulation of BC during winter. A proper representation of vertical BC load is important because the climate effects of the aerosols depend on their altitude in the atmosphere. Comparisons with measured vertical profiles indicate that the model generally overestimates the BC load, particularly at higher altitudes, and this overestimation is exacerbated with M7 compared to BULK. Both parameterizations show that north of 65° N emissions in Europe contribute most to atmospheric BC concentration and to BC in snow and ice. M7 leads to a pronounced seasonal pattern in contributions and contributions from Europe and Russia increase strongly during winter relative to BULK. There is generally an increase in the amount of BC in snow and ice with M7 compared to BULK. However, in regions where the concentration of BC in snow is strongly underestimated with BULK compared to measurements, this increase with M7 is not sufficient to significantly improve the comparison.

• Lund, Marianne Tronstad; Berntsen, Terje Koren; Fuglestvedt, Jan S.; Ponater, M & Shine, Keith P. (2012). How much information is lost by using global-mean climate metrics? an example using the transport sector. Climatic Change.  ISSN 0165-0009.  113(3-4), s 949- 963 . doi: 10.1007/s10584-011-0391-3 Vis sammendrag

  Metrics are often used to compare the climate impacts of emissions from various sources, sectors or nations. These are usually based on global-mean input, and so there is the potential that important information on smaller scales is lost. Assuming a non-linear dependence of the climate impact on local surface temperature change, we explore the loss of information about regional variability that results from using global-mean input in the specific case of heterogeneous changes in ozone, methane and aerosol concentrations resulting from emissions from road traffic, aviation and shipping. Results from equilibrium simulations with two general circulation models are used. An alternative metric for capturing the regional climate impacts is investigated. We find that the application of a metric that is first calculated locally and then averaged globally captures a more complete and informative signal of climate impact than one that uses global-mean input. The loss of information when heterogeneity is ignored is largest in the case of aviation. Further investigation of the spatial distribution of temperature change indicates that although the pattern of temperature response does not closely match the pattern of the forcing, the forcing pattern still influences the response pattern on a hemispheric scale. When the short-lived transport forcing is superimposed on present-day anthropogenic CO2 forcing, the heterogeneity in the temperature response to CO2 dominates. This suggests that the importance of including regional climate impacts in global metrics depends on whether small sectors are considered in isolation or as part of the overall climate change.

• Søvde, Ole Amund; Prather, M.J.; Isaksen, Ivar S A; Berntsen, Terje Koren; Stordal, Frode; Zhu, Xin; Holmes, Chris D. & Hsu, Juno (2012). The chemical transport model Oslo CTM3. Geoscientific Model Development.  ISSN 1991-959X.  5, s 1441- 1469 . doi: 10.5194/gmd-5-1441-2012 Vis sammendrag

  We present here the global chemical transport model Oslo CTM3, an update of the Oslo CTM2. The update comprises a faster transport scheme, an improved wet scavenging scheme for large scale rain, updated photolysis rates and a new lightning parameterization. Oslo CTM3 is better parallelized and allows for stable, large time steps for advection, enabling more complex or high spatial resolution simulations. A new treatment of the horizontal distribution of lightning is presented and found to compare well with measurements. The vertical distribution of lightning is updated and found to be a large contributor to CTM2–CTM3 differences, producing more NOx in the tropical middle troposphere, and less at the surface and at high altitudes. Compared with Oslo CTM2, Oslo CTM3 is faster, more capable and has better conceptual models for scavenging, vertical transport and fractional cloud cover. CTM3 captures stratospheric O3 better than CTM2, but shows minor improvements in terms of matching atmospheric observations in the troposphere. Use of the same meteorology to drive the two models shows that some features related to transport are better resolved by the CTM3, such as polar cap transport, while features like transport close to the vortex edge are resolved better in the Oslo CTM2 due to its required shorter transport time step. The longer transport time steps in CTM3 result in larger errors, e.g., near the jets, and when necessary the errors can be reduced by using a shorter time step. Using a time step of 30 min, the new transport scheme captures both large-scale and small-scale variability in atmospheric circulation and transport, with no loss of computational efficiency. We present a version of the new transport scheme which has been specifically tailored for polar studies, resulting in more accurate polar cap transport than the standard CTM3 transport, confirmed by comparison to satellite observations. Inclusion of tropospheric sulfur chemistry and nitrate aerosols in CTM3 is shown to be important to reproduce tropospheric O3, OH and the CH4 lifetime well.

• Tanaka, Katsumasa; Berntsen, Terje Koren; Fuglestvedt, Jan S. & Rypdal, Kristin (2012). Climate Effects of Emission Standards: The Case for Gasoline and Diesel Cars. Environmental Science and Technology.  ISSN 0013-936X.  46(9), s 5205- 5213 . doi: 10.1021/es204190w Vis sammendrag

  Passenger transport affects climate through various mechanisms involving both long-lived and short-lived climate forcers. Because diesel cars generally emit less CO2 than gasoline cars, CO2 emission taxes for vehicle registrations and fuels enhance the consumer preference for diesel cars over gasoline cars. However, with the non-CO2 components, which have been changed and will be changed under the previous and upcoming vehicle emission standards, what does the shift from gasoline to diesel cars mean for the climate mitigation? By using a simple climate model, we demonstrate that, under the earlier emissions standards (EURO 3 and 4), a diesel car causes a larger warming up to a decade after the emissions than a similar gasoline car due to the higher emissions of black carbon and NOX (enhancing the O3 production). Beyond a decade, the warming caused by a diesel car becomes, however, weaker because of the lower CO2 emissions. As the latter emissions standards (EURO 5 and 6) are phased in, the short-term warming due to a diesel car becomes smaller primarily due to the lower black carbon emissions. Thus, although results are subject to restrictive assumptions and uncertainties, the switch from gasoline to diesel cars encouraged by CO2 taxes does not contradict with the climate mitigation focusing on long-term consequences.

• Tol, Richard S J; Berntsen, Terje Koren; O’Neill, Brian C; Fuglestvedt, Jan S. & Shine, Keith P (2012). A unifying framework for metrics for aggregating the climate effect of different emissions. Environmental Research Letters.  ISSN 1748-9326.  7(4) . doi: 10.1088/1748-9326/7/4/044006 Vis sammendrag

  Multi-gas approaches to climate change policies require a metric establishing ‘equivalences’ among emissions of various species. Climate scientists and economists have proposed four kinds of such metrics and debated their relative merits. We present a unifying framework that clarifies the relationships among them. We show, as have previous authors, that the global warming potential (GWP), used in international law to compare emissions of greenhouse gases, is a special case of the global damage potential (GDP), assuming (1) a finite time horizon, (2) a zero discount rate, (3) constant atmospheric concentrations, and (4) impacts that are proportional to radiative forcing. Both the GWP and GDP follow naturally from a cost–benefit framing of the climate change issue. We show that the global temperature change potential (GTP) is a special case of the global cost potential (GCP), assuming a (slight) fall in the global temperature after the target is reached. We show how the four metrics should be generalized if there are intertemporal spillovers in abatement costs, distinguishing between private (e.g., capital stock turnover) and public (e.g., induced technological change) spillovers. Both the GTP and GCP follow naturally from a cost-effectiveness framing of the climate change issue. We also argue that if (1) damages are zero below a threshold and (2) infinitely large above a threshold, then cost-effectiveness analysis and cost–benefit analysis lead to identical results. Therefore, the GCP is a special case of the GDP. The UN Framework Convention on Climate Change uses the GWP, a simplified cost–benefit concept. The UNFCCC is framed around the ultimate goal of stabilizing greenhouse gas concentrations. Once a stabilization target has been agreed under the convention, implementation is clearly a cost-effectiveness problem. It would therefore be more consistent to use the GCP or its simplification, the GTP.

• Ødemark, Karianne; Dalsøren, Stig Bjørløw; Samset, Bjørn Hallvard; Berntsen, Terje Koren; Fuglestvedt, Jan S. & Myhre, Gunnar (2012). Short-lived climate forcers from current shipping and petroleum activities in the Arctic. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  12(4), s 1979- 1993 . doi: 10.5194/acp-12-1979-2012 Vis sammendrag

  Emissions of short-lived climate forcers (SLCF) in the Arctic region are expected to increase, notably from shipping and petroleum extraction. We here discuss changes in atmospheric SLCF concentrations and resulting radiative forcing (RF) from present day shipping and petroleum activities in the Arctic. The three-dimensional chemistry transport OsloCTM2 and a state of the art radiative forcing model are used, based on a coherent dataset of present day Arctic emissions. We find that the net RF of SLCF of shipping in the Arctic region is negative, mainly due to the direct and indirect RF effects of sulphate emissions, while the net RF of SLCF of petroleum extraction is positive, mainly due to the effects of black carbon aerosols in the air and deposited on snow. Strong seasonal variations of the sensitivities to emissions are found. In terms of annual mean values we find that the Arctic sensitivities to SLCF is similar to global average sensitivities. One exception to this is the stronger snow/ice albedo effect from BC emissions.

• Aamaas, Borgar; Bøggild, Carl Egede; Stordal, Frode; Berntsen, Terje Koren; Holmén, Kim Johan & Ström, Johan (2011). Elemental carbon deposition to Svalbard snow from Norwegian settlements and long-range transport. Tellus. Series B, Chemical and physical meteorology.  ISSN 0280-6509.  63(3), s 340- 351 . doi: 10.1111/j.1600-0889.2011.00531.x Vis sammendrag

  The impact on snow pack albedo from local elemental carbon (EC) sources in Svalbard has been investigated for the winter of 2008. Highly elevated EC concentrations in the snow are observed around the settlements of Longyearbyen and Svea (locally >1000 ng g−1, about 200 times over the background level), while EC concentrations similar to the background level are seen around Ny-Ålesund. Near Longyearbyen and Svea, darkened snow influenced by wind transported coal dust from open coal stockpiles is clearly visible from satellite images and by eye at the ground. As a first estimate, the reduction in snow albedo caused by local EC pollution from the Norwegian settlements has been compared to the estimated reduction caused by long-range transported EC for entire Svalbard. The effect of local EC from Longyearbyen, Svea and all Norwegian settlements are estimated to 2.1%, 7.9% and 10% of the total impact of EC, respectively. The EC particles tend to stay on the surface during melting, and elevated EC concentrations due to the spring melt was observed. This accumulation of EC enhances the positive albedo feedbacks. The EC concentrations were observed to be larger in metamorphosed snow than in fresh snow, and especially around ice lenses.

• Cherubini, Francesco; Peters, Glen Philip; Berntsen, Terje Koren; Strømman, Anders Hammer & Hertwich, Edgar G. (2011). CO2 emissions from biomass combustion for bioenergy: atmospheric decay and contribution to global warming. Global Change Biology Bioenergy.  ISSN 1757-1693.  3(5), s 413- 426 . doi: 10.1111/j.1757-1707.2011.01102.x Fulltekst i vitenarkiv. Vis sammendrag

  Carbon dioxide (CO2) emissions from biomass combustion are traditionally assumed climate neutral if the bioenergy system is carbon (C) flux neutral, i.e. the CO2 released from biofuel combustion approximately equals the amount of CO2 sequestered in biomass. This convention, widely adopted in life cycle assessment (LCA) studies of bioenergy systems, underestimates the climate impact of bioenergy. Besides CO2 emissions from permanent C losses, CO2 emissions from C flux neutral systems (that is from temporary C losses) also contribute to climate change: before being captured by biomass regrowth, CO2 molecules spend time in the atmosphere and contribute to global warming. In this paper, a method to estimate the climate impact of CO2 emissions from biomass combustion is proposed. Our method uses CO2 impulse response functions (IRF) from C cycle models in the elaboration of atmospheric decay functions for biomass-derived CO2 emissions. Their contributions to global warming are then quantified with a unit-based index, the GWPbio. Since this index is expressed as a function of the rotation period of the biomass, our results can be applied to CO2 emissions from combustion of all the different biomass species, from annual row crops to slower growing boreal forest.

• Hodnebrog, Øivind; Berntsen, Terje Koren; Dessens, Olivier; Gauss, Michael; Grewe, Volker; Isaksen, Ivar S A; Koffi, Brigitte; Myhre, Gunnar; Olivie, Dirk Jan Leo; Prather, Michael J; Pyle, John A.; Stordal, Frode; Szopa, Sophie; Tang, Qi; van Velthoven, Peter; Williams, Jason E & Ødemark, Karianne (2011). Future impact of non-land based traffic emissions on atmospheric ozone and OH - an optimistic scenario and a possible mitigation strategy. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  11(21), s 11293- 11317 . doi: 10.5194/acp-11-11293-2011 Vis sammendrag

  The impact of future emissions from aviation and shipping on the atmospheric chemical composition has been estimated using an ensemble of six different atmospheric chemistry models. This study considers an optimistic emission scenario (B1) taking into account e.g. rapid introduction of clean and resource-efficient technologies, and a mitigation option for the aircraft sector (B1 ACARE), assuming further technological improvements. Results from sensitivity simulations, where emissions from each of the transport sectors were reduced by 5%, show that emissions from both aircraft and shipping will have a larger impact on atmospheric ozone and OH in near future (2025; B1) and for longer time horizons (2050; B1) compared to recent time (2000). However, the ozone and OH impact from aircraft can be reduced substantially in 2050 if the technological improvements considered in the B1 ACARE will be achieved. Shipping emissions have the largest impact in the marine boundary layer and their ozone contribution may exceed 4 ppbv (when scaling the response of the 5% emission perturbation to 100% by applying a factor 20) over the North Atlantic Ocean in the future (2050; B1) during northern summer (July). In the zonal mean, ship-induced ozone relative to the background levels may exceed 12% near the surface. Corresponding numbers for OH are 6.0 × 105 molecules cm−3 and 30%, respectively. This large impact on OH from shipping leads to a relative methane lifetime reduction of 3.92 (±0.48) on the global average in 2050 B1 (ensemble mean CH4 lifetime is 8.0 (±1.0) yr), compared to 3.68 (±0.47)% in 2000. Aircraft emissions have about 4 times higher ozone enhancement efficiency (ozone molecules enhanced relative to NOx molecules emitted) than shipping emissions, and the maximum impact is found in the UTLS region. Zonal mean aircraft-induced ozone could reach up to 5 ppbv at northern mid- and high latitudes during future summer (July 2050; B1), while the relative impact peaks during northern winter (January) with a contribution of 4.2%. Although the aviation-induced impact on OH is lower than for shipping, it still causes a reduction in the relative methane lifetime of 1.68 (±0.38)% in 2050 B1. However, for B1 ACARE the perturbation is reduced to 1.17 (±0.28)%, which is lower than the year 2000 estimate of 1.30 (±0.30)%. Based on the fully scaled perturbations we calculate net radiative forcings from the six models taking into account ozone, methane (including stratospheric water vapour), and methane-induced ozone changes. For the B1 scenario, shipping leads to a net cooling with radiative forcings of −28.0 (±5.1) and −30.8 (±4.8) mW m−2 in 2025 and 2050, respectively, due to the large impact on OH and, thereby, methane lifetime reductions. Corresponding values for the aviation sector shows a net warming effect with 3.8 (±6.1) and 1.9 (±6.3) mW m−2, respectively, but with a small net cooling of -0.6 (±4.6) mW m−2 for B1 ACARE in 2050.

• Hodnebrog, Øivind; Stordal, Frode & Berntsen, Terje Koren (2011). Does the resolution of megacity emissions impact large scale ozone?. Atmospheric Environment.  ISSN 1352-2310.  45(38), s 6852- 6862 . doi: 10.1016/j.atmosenv.2011.01.012
• Lund, Marianne Tronstad & Berntsen, Terje Koren (2011). Parameterization of black carbon aging in the OsloCTM2 and implications for regional transport to the Arctic. Atmospheric Chemistry and Physics Discussions.  ISSN 1680-7367.  11, s 32499- 32534 . doi: 10.5194/acpd-11-32499-2011 Vis sammendrag

  A critical parameter for the atmospheric lifetime of black carbon (BC) aerosols, and hence for the range over which the particles can be transported, is the aging time, i.e. the time before the aerosols become available for removal by wet deposition. This study compares two different parameterizations of BC aging in the chemistry transport model OsloCTM2: (i) a bulk parameterization (BULK) where aging is represented by a constant transfer to hydrophilic mode and (ii) a microphysical module (M7) where aging occurs through particle interaction and where the particle size distribution is accounted for. We investigate the effect of including microphysics on the distribution of BC globally and in the Arctic. We also focus on the impact on estimated contributions to Arctic BC from selected emission source regions. With more detailed microphysics (M7) there are regional and seasonal variations in aging. The aging is slower during high-latitude winter, when the production of sulfate is lower, than in lower latitudes and during summer. High-latitude concentrations of BC are significantly increased during winter compared to BULK. Furthermore, M7 improves the model performance at high Arctic surface stations, especially the accumulation of BC during winter. A proper representation of vertical BC load is important because the climate effects of the aerosols depend on their altitude in the atmosphere. Comparisons with measured vertical profiles indicate that the model generally overestimates the BC load, particularly at higher altitudes, and this overestimation is exacerbated with M7 compared to BULK. Both parameterizations show that north of 65° N emissions in Europe contribute most to atmospheric BC concentration and to BC in snow and ice. M7 leads to a pronounced seasonal pattern in contributions and contributions from Europe and Russia increase strongly during winter compared to BULK. There is generally a small increase in the amount of BC in snow and ice with M7 compared to BULK, but concentrations are still underestimated relative to measurements.

• Myhre, Gunnar; Fuglestvedt, Jan S.; Berntsen, Terje Koren & Lund, Marianne Tronstad (2011). Mitigation of short-lived heating components may lead to unwanted long-term consequences. Atmospheric Environment.  ISSN 1352-2310.  45(33), s 6103- 6106 . doi: 10.1016/j.atmosenv.2011.08.009 Vis sammendrag

  A mitigation strategy for reducing emissions of short-lived heating components such as black carbon (BC) aerosols and ozone precursors to limit global warming has frequently been suggested. BC emissions influence the radiative balance in several ways through direct and semi-direct aerosol effects, as well as by impacting the surface albedo, and their net effect is likely a warming that enhances the total man-made warming. However, the role that BC or other short-lived heating components may play in future mitigation strategies must be formulated with caution to avoid unforeseen and unwanted consequences. A near-term mitigation of short-lived heating components could lead to a delayed action on CO2 and other long-lived greenhouse gases and thus an increased long-term warming. A key element is whether policies are designed as a consequence of predicted warming or observed warming. Without a clear strategy, early BC or ozone reductions may even lead to an unexpectedly larger temperature change.

• Myhre, Gunnar; Shine, K. P.; Rädel, G.; Gauss, Michael; Isaksen, Ivar S A; Tang, Q; Prather, M.J.; Williams, J.E.; van Velthoven, P; Dessens, O.; Koffi, B.; Szopa, S; Hoor, P.; Grewe, V; Borken-Kleefeld, J; Berntsen, Terje Koren & Fuglestvedt, Jan S. (2011). Radiative forcing due to changes in ozone and methane caused by the transport sector. Atmospheric Environment.  ISSN 1352-2310.  45(2), s 387- 394 . doi: 10.1016/j.atmosenv.2010.10.001 Vis sammendrag

  The year 2000 radiative forcing (RF) due to changes in O3 and CH4 (and the CH4-induced stratospheric water vapour) as a result of emissions of short-lived gases (oxides of nitrogen (NOx), carbon monoxide and non-methane hydrocarbons) from three transport sectors (ROAD, maritime SHIPping and AIRcraft) are calculated using results from five global atmospheric chemistry models. Using results from these models plus other published data, we quantify the uncertainties. The RF due to short-term O3 changes (i.e. as an immediate response to the emissions without allowing for the long-term CH4 changes) is positive and highest for ROAD transport (31 mW m−2) compared to SHIP (24 mW m−2) and AIR (17 mW m−2) sectors in four of the models. All five models calculate negative RF from the CH4 perturbations, with a larger impact from the SHIP sector than for ROAD and AIR. The net RF of O3 and CH4 combined (i.e. including the impact of CH4 on ozone and stratospheric water vapour) is positive for ROAD (+16(±13) (one standard deviation) mW m−2) and AIR (+6(±5) mW m−2) traffic sectors and is negative for SHIP (−18(±10) mW m−2) sector in all five models. Global Warming Potentials (GWP) and Global Temperature change Potentials (GTP) are presented for AIR NOx emissions; there is a wide spread in the results from the 5 chemistry models, and it is shown that differences in the methane response relative to the O3 response drive much of the spread.

• Peters, Glen Philip; Aamaas, Borgar; Berntsen, Terje Koren & Fuglestvedt, Jan S. (2011). The integrated Global Temperature change Potential (iGTP)and relationships between emission metrics. Environmental Research Letters.  ISSN 1748-9326.  6(4) . doi: 10.1088/1748-9326/6/4/044021 Vis sammendrag

  The Kyoto Protocol compares greenhouse gas emissions (GHGs) using the global warming potential (GWP) with a 100 yr time-horizon. The GWP was developed, however, to illustrate the difficulties in comparing GHGs. In response, there have been many critiques of the GWP and several alternative emission metrics have been proposed. To date, there has been little focus on understanding the linkages between, and interpretations of, different emission metrics. We use an energy balance model to mathematically link the absolute GWP, absolute global temperature change potential (AGTP), absolute ocean heat perturbation (AOHP), and integrated AGTP. For pulse emissions, energy conservation requires that AOHP = AGWP − iAGTP/λ and hence AGWP and iAGTP are closely linked and converge as AOHP decays to zero. When normalizing the metrics with CO2 (GWP, GTP, and iGTP), we find that the iGTP and GWP are similar numerically for a wide range of GHGs and time-horizons, except for very short-lived species. The similarity between the iGTPX and GWPX depends on how well a pulse emission of CO2 can substitute for a pulse emission of X across a range of time-horizons. The ultimate choice of emission metric(s) and time-horizon(s) depends on policy objectives. To the extent that limiting integrated temperature change over a specific time-horizon is consistent with the broader objectives of climate policy, our analysis suggests that the GWP represents a relatively robust, transparent and policy-relevant emission metric.

• Skeie, Ragnhild Bieltvedt; Berntsen, Terje Koren; Myhre, Gunnar; Pedersen, Christina Alsvik; Ström, Johan; Gerland, Sebastian & Ogren, JA (2011). Black carbon in the atmosphere and snow, from pre-industrial times until present. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  11(14), s 6809- 6836 . doi: 10.5194/acp-11-6809-2011 Vis sammendrag

  The distribution of black carbon (BC) in the atmosphere and the deposition of BC on snow surfaces since pre-industrial time until present are modelled with the Oslo CTM2 model. The model results are compared with observations including recent measurements of BC in snow in the Arctic. The global mean burden of BC from fossil fuel and biofuel sources increased during two periods. The first period, until 1920, is related to increases in emissions in North America and Europe, and the last period after 1970 are related mainly to increasing emissions in East Asia. Although the global burden of BC from fossil fuel and biofuel increases, in the Arctic the maximum atmospheric BC burden as well as in the snow was reached in 1960s, with a slight reduction thereafter. The global mean burden of BC from open biomass burning sources has not changed significantly since 1900. With current inventories of emissions from open biomass sources, the modelled burden of BC in snow and in the atmosphere north of 65° N is small compared to the BC burden of fossil fuel and biofuel origin. From the concentration changes radiative forcing time series due to the direct aerosol effect as well as the snow-albedo effect is calculated for BC from fossil fuel and biofuel. The calculated radiative forcing in 2000 for the direct aerosol effect is 0.35 W m−2 and for the snow-albedo effect 0.016 W m−2 in this study. Due to a southward shift in the emissions there is an increase in the lifetime of BC as well as an increase in normalized radiative forcing, giving a change in forcing per unit of emissions of 26 % since 1950.

• Skeie, Ragnhild Bieltvedt; Berntsen, Terje Koren; Myhre, Gunnar; Tanaka, Katsumasa; Kvalevåg, Maria Malene & Hoyle, Christopher (2011). Anthropogenic radiative forcing time series from pre-industrial times until 2010. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  11, s 11827- 11857 . doi: 10.5194/acp-11-11827-2011 Vis sammendrag

  In order to use knowledge of past climate change to improve our understanding of the sensitivity of the climate system, detailed knowledge about the time development of radiative forcing (RF) of the earth atmosphere system is crucial. In this study, time series of anthropogenic forcing of climate from pre-industrial times until 2010, for all well established forcing agents, are estimated. This includes presentation of RF histories of well mixed greenhouse gases, tropospheric ozone, direct- and indirect aerosol effects, surface albedo changes, stratospheric ozone and stratospheric water vapour. For long lived greenhouse gases, standard methods are used for calculating RF, based on global mean concentration changes. For short lived climate forcers, detailed chemical transport modelling and radiative transfer modelling using historical emission inventories is performed. For the direct aerosol effect, sulphate, black carbon, organic carbon, nitrate and secondary organic aerosols are considered. For aerosol indirect effects, time series of both the cloud lifetime effect and the cloud albedo effect are presented. Radiative forcing time series due to surface albedo changes are calculated based on prescribed changes in land use and radiative transfer modelling. For the stratospheric components, simple scaling methods are used. Long lived greenhouse gases (LLGHGs) are the most important radiative forcing agent with a RF of 2.83±0.28 W m−2 in year 2010 relative to 1750. The two main aerosol components contributing to the direct aerosol effect are black carbon and sulphate, but their contributions are of opposite sign. The total direct aerosol effect was −0.48±0.32 W m−2 in year 2010. Since pre-industrial times the positive RF (LLGHGs and tropospheric O3) has been offset mainly by the direct and indirect aerosol effects, especially in the second half of the 20th century, which possibly lead to a decrease in the total anthropogenic RF in the middle of the century. We find a total anthropogenic RF in year 2010 of 1.4 W m−2. However, the uncertainties in the negative RF from aerosols are large, especially for the cloud lifetime effect.

• Berntsen, Terje Koren; Tanaka, Katsumasa & Fuglestvedt, Jan S. (2010). Does black carbon abatement hamper CO2 abatement? A letter. Climatic Change.  ISSN 0165-0009.  103(3-4), s 627- 633 . doi: 10.1007/s10584-010-9941-3 Vis sammendrag

  Concerns have been raised that near-term black carbon abatement strategies for global warming mitigation would interfere with the longer-term CO2 abatement efforts. In response, we put forward a “combined target and metric approach”, a theoretical framework, in which the time horizon of the metric is linked to the specific target of the climate policy. In this approach, a shorter time horizon for the metric is justified only when the overall climate policy is tightened; the lower the target level of the climate policy, the earlier the year of the target. Employing a consistent time perspective for the metric and target means that enhanced near-term reduction of short-lived climate forcers does not reduce the importance of the CO2 abatement, since the overall climate target is stricter.

• Borken-Kleefeld, J; Berntsen, Terje Koren & Fuglestvedt, Jan S. (2010). Specific Climate Impact of Passenger and Freight Transport. Environmental Science and Technology.  ISSN 0013-936X.  44(15), s 5700- 5706 . doi: 10.1021/es9039693 Vis sammendrag

  Emissions of short-lived species contribute significantly to the climate impact of transportation. The magnitude of the effects varies over time for each transport mode. This paper compares first the absolute climate impacts of current passenger and freight transportation. Second, the impacts are normalized with the transport work performed and modes are compared. Calculations are performed for the integrated radiative forcing and mean temperature change, for different time horizons and various measures of transport work. An unambiguous ranking of the specific climate impact can be established for freight transportation, with shipping and rail having lowest and light trucks and air transport having highest specific impact for all cases calculated. Passenger travel with rail, coach or two- and three-wheelers has on average the lowest specific climate impact also on short time horizons. Air travel has the highest specific impact on short-term warming, while on long-term warming car travel has an equal or higher impact per passenger-kilometer.

• Eyring, Veronika; Isaksen, Ivar S A; Berntsen, Terje Koren; Collins, William J.; Corbett, James J.; Endresen, Øyvind; Grainger, Roy G.; Moldanova, Jana; Schlager, Hans & Stevenson, David S. (2010). Transport impacts on atmosphere and climate: Shipping. Atmospheric Environment.  ISSN 1352-2310.  44(37), s 4735- 4771 . doi: 10.1016/j.atmosenv.2009.04.059 Vis sammendrag

  Emissions of exhaust gases and particles from oceangoing ships are a significant and growing contributor to the total emissions from the transportation sector. We present an assessment of the contribution of gaseous and particulate emissions from oceangoing shipping to anthropogenic emissions and air quality. We also assess the degradation in human health and climate change created by these emissions. Regulating ship emissions requires comprehensive knowledge of current fuel consumption and emissions, understanding of their impact on atmospheric composition and climate, and projections of potential future evolutions and mitigation options. Nearly 70% of ship emissions occur within 400 km of coastlines, causing air quality problems through the formation of ground-level ozone, sulphur emissions and particulate matter in coastal areas and harbours with heavy traffic. Furthermore, ozone and aerosol precursor emissions as well as their derivative species from ships may be transported in the atmosphere over several hundreds of kilometres, and thus contribute to air quality problems further inland, even though they are emitted at sea. In addition, ship emissions impact climate. Recent studies indicate that the cooling due to altered clouds far outweighs the warming effects from greenhouse gases such as carbon dioxide (CO2) or ozone from shipping, overall causing a negative present-day radiative forcing (RF). Current efforts to reduce sulphur and other pollutants from shipping may modify this. However, given the short residence time of sulphate compared to CO2, the climate response from sulphate is of the order decades while that of CO2 is centuries. The climatic trade-off between positive and negative radiative forcing is still a topic of scientific research, but from what is currently known, a simple cancellation of global mean forcing components is potentially inappropriate and a more comprehensive assessment metric is required. The CO2 equivalent emissions using the global temperature change potential (GTP) metric indicate that after 50 years the net global mean effect of current emissions is close to zero through cancellation of warming by CO2 and cooling by sulphate and nitrogen oxides.

• Fuglestvedt, Jan S.; Shine, K. P.; Berntsen, Terje Koren; Cook, J.; Lee, D. S.; Stenke, A.; Skeie, Ragnhild Bieltvedt; Velders, G. J. M. & Waitz, I. A. (2010). Transport impacts on atmosphere and climate: Metrics. Atmospheric Environment.  ISSN 1352-2310.  44(37), s 4648- 4677 . doi: 10.1016/j.atmosenv.2009.04.044 Vis sammendrag

  The transport sector emits a wide variety of gases and aerosols, with distinctly different characteristics which influence climate directly and indirectly via chemical and physical processes. Tools that allow these emissions to be placed on some kind of common scale in terms of their impact on climate have a number of possible uses such as: in agreements and emission trading schemes; when considering potential trade-offs between changes in emissions resulting from technological or operational developments; and/or for comparing the impact of different environmental impacts of transport activities. Many of the non-CO2 emissions from the transport sector are short-lived substances, not currently covered by the Kyoto Protocol. There are formidable difficulties in developing metrics and these are particularly acute for such short-lived species. One difficulty concerns the choice of an appropriate structure for the metric (which may depend on, for example, the design of any climate policy it is intended to serve) and the associated value judgements on the appropriate time periods to consider; these choices affect the perception of the relative importance of short- and long-lived species. A second difficulty is the quantification of input parameters (due to underlying uncertainty in atmospheric processes). In addition, for some transport-related emissions, the values of metrics (unlike the gases included in the Kyoto Protocol) depend on where and when the emissions are introduced into the atmosphere – both the regional distribution and, for aircraft, the distribution as a function of altitude, are important. In this assessment of such metrics, we present Global Warming Potentials (GWPs) as these have traditionally been used in the implementation of climate policy. We also present Global Temperature Change Potentials (GTPs) as an alternative metric, as this, or a similar metric may be more appropriate for use in some circumstances. We use radiative forcings and lifetimes from the literature to derive GWPs and GTPs for the main transport-related emissions, and discuss the uncertainties in these estimates. We find large variations in metric (GWP and GTP) values for NOx, mainly due to the dependence on location of emissions but also because of inter-model differences and differences in experimental design. For aerosols we give only global-mean values due to an inconsistent picture amongst available studies regarding regional dependence. The uncertainty in the presented metric values reflects the current state of understanding; the ranking of the various components with respect to our confidence in the given metric values is also given. While the focus is mostly on metrics for comparing the climate impact of emissions, many of the issues are equally relevant for stratospheric ozone depletion metrics, which are also discussed.

• Lee, D.S; Pitari, G; Grewe, V; Gierens, K; Penner, JE; Petzold, A; Prather, MJ; Schumann, U.; Bais, A; Berntsen, Terje Koren; Iachetti, D; Lim, LL & Sausen, R (2010). Transport impacts on atmosphere and climate: Aviation. Atmospheric Environment.  ISSN 1352-2310.  44(37), s 4678- 4734 . doi: 10.1016/j.atmosenv.2009.06.005

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• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Berntsen, Terje Koren; Kauserud, Håvard; Büker, Patrick; Emberson, Lisa D. & Stordal, Frode (2018). The double punch: ozone and climate stresses to sub-Arctic vegetation.
• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Falk, Stefanie; Berntsen, Terje Koren; Kauserud, Håvard; Emberson, Lisa D. & Stordal, Frode (2018). Project The double punch: ozone and climate stresses on vegetation.
• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Kauserud, Håvard; Berntsen, Terje Koren & Stordal, Frode (2018). The double punch: ozone and climate stresses on vegetation.
• Aas, Kjetil Schanke; Westermann, Sebastian; Martin, Leo Celestin Paul & Berntsen, Terje Koren (2017). Degrading Palsa Mires in Northern Norway Simulated with a Regional Climate Model with a Subgrid Snow Scheme.
• Bryn, Anders; Potthoff, Kerstin; Horvath, Peter; Volden, Inger Kristine; Tang, Hui; Berntsen, Terje Koren & Stordal, Frode (2017). Greening and browning: 100 years of tree- and forest line dynamics..
• Bryn, Anders; Stordal, Frode; Berntsen, Terje Koren & Tang, Hui (2017). Vegetation dynamics - distribution, modelling and feedbacks..
• Jeanette, Viken; Vollsnes, Ane Victoria; Eriksen, Aud Else Berglen; Berntsen, Terje Koren & Stordal, Frode (2017). DO3SEiNORD.
• Lund, Marianne Tronstad; Berntsen, Terje Koren & Fuglestvedt, Jan S. (2017). Climate response to ozone perturbations at different altitudes and latitudes.
• Tang, Hui; Stordal, Frode; Berntsen, Terje Koren & Bryn, Anders (2017). Improve dynamic vegetation model of community land model in simulating Arctic vegetation and its interaction with climate..
• Lund, Marianne Tronstad; Aamaas, Borgar; Berntsen, Terje Koren & Fuglestvedt, Jan S. (2016). Luftfart og klima - En oppdatert oversikt over status for forskning på klimaeffekter av utslipp fra fly. CICERO Report. 05. Vis sammendrag

  Denne rapporten gir en oppdatert oversikt over hvordan og i hvilken grad de ulike utslippene fra flytrafikk påvirker klima basert på den nyeste forskningen. For å forstå den totale klimaeffekten av luftfart er det viktig å inkludere alle mekanismene som bidrar til klimapåvirkning, samt hvordan disse kan vektes og sammenlignes på tvers av ulike skalaer i tid og rom. Dette er hovedfokus i denne rapporten. Rapporten er en oppdatering av Lund m.fl. (2011) og fokuserer på forskningsresultater siden da. Arbeidet er finansiert av Avinor

• Tang, Hui; Stordal, Frode; Berntsen, Terje Koren & Bryn, Anders (2016). Dynamical vegetation-atmosphere modelling of the boreal zone.
• Skeie, Ragnhild Bieltvedt; Fuglestvedt, Jan S.; Allen, Myles R.; Berntsen, Terje Koren & Peters, Glen Philip (2015). National and regional contributions to global climate change.
• Aas, Kjetil Schanke; Berntsen, Terje Koren; Boike, Julia; Etzelmuller, Bernd; Gisnås, Kjersti & Westermann, Sebastian (2014). Simulating the surface energy balance on Svalbard with the Weather Research and Forecasting model.
• Aas, Kjetil Schanke; Dunse, Thorben; Collier, Emily; Schuler, Thomas; Kohler, Jack & Berntsen, Terje Koren (2014). Simulating the Climatic Mass Balance of Svalbard Glaciers from 2003 to 2014 Using a Coupled Atmosphere and Climatic Mass-Balance Model.
• Dalsøren, Stig Bjørløw; Fuglestvedt, Jan S.; Samset, Bjørn Hallvard; Berntsen, Terje Koren; Myhre, Gunnar; Eide, Lars Ingolf; Eide, Magnus Strandmyr; Bergh, Trond Flisnes; Peters, Glen Philip & Ødemark, Karianne (2014). Does routing matter? Radiative forcing and temperature responses to Arctic transit shipping versus traditional Suez route.
• Hodnebrog, Øivind; Aamaas, Borgar; Berntsen, Terje Koren; Fuglestvedt, Jan S.; Myhre, Gunnar; Samset, Bjørn Hallvard & Søvde, Ole Amund (2014). Climate impact of short-lived climate forcers: A case study of emissions from Norway.
• Aas, Kjetil Schanke; Berntsen, Terje Koren; Boike, Julia; Etzelmuller, Bernd; Kristjansson, Jon Egill; Schuler, Thomas; Stordal, Frode & Westermann, Sebastian (2013). Observed and simulated SEB at Ny-Ålesund, Svalbard.
• Aas, Kjetil Schanke; Berntsen, Terje Koren; Boike, Julia; Etzelmuller, Bernd; Kristjansson, Jon Egill; Schuler, Thomas; Stordal, Frode & Westermann, Sebastian (2013). Observed and simulated surface energy budget at Ny-Ålesund, Svalbard.
• Aas, Kjetil Schanke; Berntsen, Terje Koren; Boike, Julia; Etzelmuller, Bernd; Kristjansson, Jon Egill; Schuler, Thomas; Stordal, Frode & Westermann, Sebastian (2013). Observert og simulert bakke-energibalanse på Svalbard.
• Berntsen, Terje Koren; Klimont, Zbigniew & Heyes, Chris (2013). Contribution of diesel vehicle emissions to Arctic black carbon in the OsloCTM2.
• Etzelmuller, Bernd; Westermann, Sebastian; Berntsen, Terje Koren; Dunse, Thorben; Gisnås, Kjersti; Hagen, Jon Ove Methlie; Kristjansson, Jon Egill; Isaksen, Ketil; Vikhamar Schuler, Dagrun; Schuler, Thomas; Stordal, Frode & Aas, Kjetil Schanke (2013). CRYOMET – Concept and Results for Bridging Models Between the Atmosphere and the Terrestrial Cryosphere (Glacier and Permafrost).
• Etzelmuller, Bernd; Westermann, Sebastian; Berntsen, Terje Koren; Gisnås, Kjersti; Hagen, Jon Ove Methlie; Kristjansson, Jon Egill; Schuler, Thomas; Vikhamar Schuler, Dagrun; Stordal, Frode & Aas, Kjetil Schanke (2013). Bridging models for the terrestrial cryosphere and the atmosphere - The CryoMET project.
• Aas, Kjetil Schanke; Berntsen, Terje Koren; Westermann, Sebastian & Etzelmuller, Bernd (2012). Observations and plans for simulations of surface energy balance on Svalbard, Norway.
• Hodnebrog, Øivind; Stordal, Frode; Isaksen, Ivar S A; Gauss, Michael; Berntsen, Terje Koren & Hov, Øystein (2012). Modelling tropospheric ozone production on different scales.
• Lund, Marianne Tronstad & Berntsen, Terje Koren (2012). Parameterization of black carbon aging in the OsloCTM2.
• Peters, Glen Philip; Aamaas, Borgar; Berntsen, Terje Koren & Fuglestvedt, Jan S. (2012). The integrated Global Temperature change Potential (iGTP) and relationships between emission metrics.
• Skeie, Ragnhild Bieltvedt; Berntsen, Terje Koren; Aldrin, Magne & Holden, Marit (2012). Using modelled historical concentrations of short lived climate components to constrain the climate sensitivity. META.  ISSN 1890-2987.  (2), s 8- 11
• Skeie, Ragnhild Bieltvedt; Berntsen, Terje Koren; Aldrin, Magne; Holden, Marit & Myhre, Gunnar (2012). Constraining climate sensitivity by observations and models.
• Westermann, Sebastian; Berntsen, Terje Koren; Etzelmuller, Bernd; Gisnås, Kjersti; Hagen, Jon Ove Methlie; Kristjansson, Jon Egill; Schuler, Thomas & Stordal, Frode (2012). The CryoMET project – combining deterministic and probabilistic downscaling to model snow depth over a wide range of scales.
• Borken-Kleefeld, J; Berntsen, Terje Koren & Fuglestvedt, Jan S. (2011). Times Matter!-Response to Wallington et al. Environmental Science and Technology.  ISSN 0013-936X.  45(7), s 3167- 3168 . doi: 10.1021/es200343n
• Lund, Marianne Tronstad; Berntsen, Terje Koren & Fuglestvedt, Jan S. (2011). Luftfart og klima- En oppdatert oversikt over status for forskning på klimaeffekter av utslipp fra fly.
• Lund, Marianne Tronstad; Berntsen, Terje Koren; Fuglestvedt, Jan S.; Ponater, Michael & Shine, Keith P. (2011). How much information is lost by using global-mean climate metrics? An example using the transport sector.
• Søvde, Ole Amund; Prather, M.J.; Berntsen, Terje Koren; Myhre, Gunnar & Isaksen, Ivar S A (2011). Oslo CTM3; a global chemical transport model.
• Cherubini, Francesco; Peters, Glen Philip; Berntsen, Terje Koren; Strømman, Anders Hammer; Michelsen, Ottar & Hertwich, Edgar G. (2010). Bioenergy and its actual mitigation of climate change: does carbon neutral mean climate neutral?.
• Cherubini, Francesco; Peters, Glen Philip; Berntsen, Terje Koren; Strømman, Anders Hammer; Michelsen, Ottar & Hertwich, Edgar G. (2010). Biogenic CO2 emissions and their contribution to climate change.
• Stordal, Frode; Kristjansson, J.E.; Berntsen, Terje Koren; Tallaksen, Lena; Xu, Chong Yu; Giorgio, Filippo; Berg, Trygve & Aaheim, Asbjørn (2010). Socioeconomic consequences of climate change in Sub-equatorial Africa related to the agricultural sector. Vis sammendrag

  In Africa future climate change is projected to lead to a warming which is very likely to be larger than the global average throughout the continent. The sub-Saharan regions in the north are now studied through a cluster of international research programmes. Although there have been regional studies of climate change in sub-equatorial Africa less attention has been paid to climate change over the African regions south of the equator. The need for a greater focus on this region is made more urgent by the potential vulnerability to climate change indicated by the most recent model projections. In large parts of sub-equatorial Africa a significant increase in most indicators of heavy precipitation events have been found, as e.g. the number of days with precipitation above 10 mm. At the same time the maximum number of consecutive dry days shows in general an increase. The total amount of precipitation has decreased, the dry spells are more frequent, but at the same time the heavy precipitation events are increasing. This is challenging for many sectors, in particular agriculture. An interdisciplinary project is recently initiated to address adaptation to climate change in the agricultural sector, entitled ?Socioeconomic Consequences of Climate Change in Sub-equatorial Africa? (SoCoCA). It is financed by the Research Council of Norway (FRIMUF program) and is coordinated by the University of Oslo, Department of Geosciences, which contributes with global climate model calculations. The International Centre for Theoretical Physics (ICTP), Trieste, Italy, which has specialized in regional climate modelling, contributes with calculations for the study region. Regional hydrological modelling is performed by the coordinating institute. University of Life Sciences, Noragric, Ås, Norway, assesses challenges for the agricultural sector resulting from the projected climate change, and Center for Climate and Environmental Research ? Oslo. (CICERO) estimates socioeconomic consequences by the use of a general equilibrium model.

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