Oslo joint seminar in atmospheric, ocean and climate science, Andrew Gettelman
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.
Speaker: Andrew Gettelman (NCAR)
Processes responsible for Forcing and Feedback in the Community Earth System Model version 2
The evolution of future climate is a dictated by how climate will be forced, and how it will respond to the forcing. To determine the sensitivity of the earth system, both forcing and response (or feedback) must be estimated. In theory the climate response in present day is also a combination of forcing and feedbacks, so if the forcing is known then the total feedback can be estimated. Forcing of the earth system on timescales of up to a century or so is largely from radiative forcing from long and short lived greenhouse gases and forcing from cloud adjustments due to aerosols (aerosol cloud interactions). The response of the system to this net forcing is termed the climate feedback. These are internal adjustments. Cloud responses are the largest uncertainty in estimating climate feedbacks, making clouds critical for both forcing and feedback.
This presentation will describe evolution of climate forcing and climate feedbacks in the Community Earth System Model version 2 (very similar to NorESM2). CESM2 has the lowest error metrics against observations of any NCAR climate model. But there is evidence that there are very strong forcing and feedbacks in the system. Forcing and feedback are a useful framework for testing which processes are critical important for the evolution of the earth's radiation budget and surface temperature response in the model. Many of these critical processes are related to clouds and aerosols. The presentation will discuss some of these detailed explorations, how critical processes for clouds work and respond, and how we can constrain these processes from observations.