A126-03
Climate feedbacks through chemistry and aerosols in CMIP6 Earth system models
Friday, 11 December 2020: 10:38
Virtual
William Collins1, Gillian Thornhill2, Dirk Olivié3, Alexander T Archibald4, Susanne Bauer5, Gerd Folberth6, Ramiro Checa-Garcia7, Stephanie Fiedler8, Ada Gjermundsen9, Larry Wayne Horowitz10, J F Lamarque11, Martine Michou12, Jane Patricia Mulcahy13, Pierre Nabat14, Vaishali Naik10, Fabien Paulot15, Michael Schulz16, Catherine Scott17, Fiona M O'Connor18, Roland Séférian19, Christopher James Smith20, Toshihiko Takemura21, Simone Tilmes22 and James Weber4, (1)University of Reading, Reading, RG6, United Kingdom, (2)University of Reading, Reading, United Kingdom, (3)University of Oslo, Oslo, Norway, (4)University of Cambridge, Cambridge, United Kingdom, (5)NASA Goddard Institute for Space Studies, New York, United States, (6)Met Office Hadley center for Climate Change, ESMS, Exeter, United Kingdom, (7)Karlsruhe Institute of Technology, Karlsruhe, Germany, (8)University of Cologne, Institute of Geophysics and Meteorology, Cologne, Germany, (9)University of Oslo, Department of Geosciences, Oslo, Norway, (10)NOAA GFDL, Princeton, NJ, United States, (11)NCAR, Boulder, CO, United States, (12)Météo-France Toulouse, Toulouse Cedex 01, France, (13)Met Office Hadley Centre for Climate Change, Exeter, United Kingdom, (14)METEO FRANCE/CNRM, Toulouse, France, (15)NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, United States, (16)Norwegian Meteorological Institute, Climate and Air Pollution Section, Oslo, Norway, (17)University of Leeds, School of Earth and Environment, Leeds, United Kingdom, (18)UK Met Office, Exeter, United Kingdom, (19)Meteo-France - CNRS, CNRM, CEN, Toulouse, France, (20)Center for International Climate and Environmental Research Oslo, Oslo, Norway, (21)Kyushu University, Research Institute for Applied Mechanics, Fukuoka, Japan, (22)National Center for Atmospheric Research, Atmospheric Chemistry, Observations, and Modeling Laboratory, Boulder, CO, United States
Abstract:
We addresses the multiple pathways for climate feedbacks through aerosol and chemical processes in Earth system models. Changes in climate lead to changes in the abundance of aerosols and reactive gases particularly through changing their natural emissions and also through affecting removal processes. These changes in abundance in turn affect climate, so amplifying or dampening the initial effect. These chemistry and aerosol feedbacks can be expressed as W/m2/K and so directly compared with the physical feedbacks.
Chemical feedbacks play a fundamental role in determining the magnitude of the response of the climate system to external forcing from anthropogenic emissions. The latest generation of Earth system models (ESMs) include aerosol and chemistry components that interact with each other and with the biosphere. These interactions introduce a complex web of feedbacks which it is important to understand and quantify. We analyse these processes in the CMIP6 ESMs, quantifying the impact of climate change on changes in natural emissions of aerosols (dust, sea salt, sulphate) and reactive gases (methane, NOx, VOCs), changes in chemical reaction rates (methane and ozone) and changes in wet/dry deposition. Expected changes in methane are diagnosed analytically from emissions and loss rates. We also quantify the radiative impacts of these changes, and hence the climate feedback (in W/m2/K) from each process.
We find that the overall climate feedback through chemistry and aerosols is negative (-0.23+/-0.12 W/m2/K) in the Earth system model results submitted to CMIP6 due to increased negative forcing from increased natural aerosol emissions with warmer temperatures. Through diagnosing changes in methane emissions and lifetime we find that if Earth system models were to allow methane to vary interactively, methane’s positive feedbacks (principally wetland methane emissions and biogenic VOC emissions) would offset much of the aerosol feedbacks.
