Oslo joint seminar in atmospheric, ocean and climate science, Mar. 05

Title: The relatively-neglected shortwave forcing by greenhouse gases

Speaker:   Keith Shine, Univ of Reading

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Speaker:

Keith Shine, Univ of Reading

Abstract:  

Greenhouse gas radiative forcing is predominantly caused by the impact on outgoing longwave radiation. But greenhouse gases generally have many absorption bands in the solar near-infrared (wavelengths  0.7 - 4 microns). CO2's solar absorption has long been known to reduce its forcing by about 5%; this is a small but non-trivial effect (e.g. it's about the size of the forcing due to aircraft contrails). Our recent calculations indicate that methane's shortwave bands enhance its forcing by 10-15%. Aspects of the solar forcing by greenhouse gases unsettle a radiative forcing geek like me. What properties of a gas make it more likely to have a significant shortwave forcing? Why does the sign of solar forcing differ between gases? Why does the sign of solar forcing differ between the "traditional" radiative forcing definition, and the more recently adopted "effective radiative forcing"? And why does the longwave/shortwave partitioning of forcing differ between tropopause and top-of-atmosphere perspectives? Using idealised and more-realistic simulations, I attempt to make some sense of this.

 

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.

Published Jan. 9, 2020 1:52 PM - Last modified Feb. 26, 2020 10:35 AM