Oslo joint seminar in atmospheric, ocean and climate science, Apr. 25
Title: Earth’s surface radiation budget and its changes over time
Speaker: Martin Wild, ETH-Zürich
Martin Wild, ETH-Zürich
The surface radiation budget is a key determinant of the climate of our environments and provides the energy for a variety of climate-relevant processes. While the net radiative energy fluxes in and out of the climate system at the top of atmosphere (TOA) are now known with considerable accuracy from new satellite programs such as CERES and SORCE, the corresponding fluxes at the Earth’s surface, which cannot be directly measured from space, are afflicted with much larger uncertainties. This is reflected in greatly diverging global estimates of the surface energy balance components that have been published over the years. Accordingly, also climate models still largely differ in their representation of these components. Since the mid-1990s, accurate direct measurements become increasingly available from the networks of surface radiation stations, such as the Baseline Surface Radiation Network (BSRN), which we use in an attempt to better constrain the energy fluxes at the Earth’s surface.
From the historic surface radiation records we further learned that the surface radiative fluxes are not just stable over time but undergo significant changes on decadal timescales. This applies not only for the thermal fluxes as expected from the increasing greenhouse effect, but also for the amount of solar radiation that reaches the Earth’s surface. Surface solar radiation records indicate a reduction of surface solar radiation from the 1950s to the 1980s at widespread observation sites, popularly known as “global dimming” and a partial recovery thereafter, known as “brightening”. The magnitude and causes of these multidecadal variations are still under investigation. More widely measured quantities, such as sunshine duration, diurnal temperature range or pan evaporation measurements, may serve as proxy for surface shortwave radiation, and may be able to expand the information contained in the limited number of direct radiation measurements both in time and space. To better understand the role of clouds and aerosols in the context of dimming and brightening we make attempts to infer trends under both all-sky and clear-sky conditions in surface radiation records which provide sufficiently high temporal resolution (minutes up to daily) to allow for the identification of cloud-free periods. There are indications that dimming and brightening may have substantially affected various aspects of climate and environmental change, such as global warming rates and the diurnal temperature range, the intensity of the global water cycle, glacier retreat, photosynthesis and biosphere growth, as well as, on a more applied level, solar electric power production. Some examples are given.
What is the Joint Oslo Seminar (JOS):
Atmospheric and climate sciences have a stronghold in Oslo among the four institutions University of Oslo, the Meteorological Institute, CICERO and NILU. This joint seminar invites renowned international experts to contribute to an informal series of lectures, meant to create interaction with the Oslo atmospheric and climate science community on recent highlights and analysis in the field. All seminars will be held on Thursdays (Noon -1pm) and lunch (sandwiches) will be served on a “first-come-first-served”-basis.