Improving Atmospheric Chemistry in Climate Models
Climate model simulations include the influences of atmospheric chemistry and aerosols, yet there are uncertainties in how models formulate and parameterize chemistry, aerosols, and their influence on Earth’s radiation, clouds, and other climate features. The latest phase of the international Climate Model Intercomparison Project (CMIP) included a parallel effort in which model groups compared the treatment and effect of chemistry and aerosols in climate models (Atmospheric Chemistry and Climate Model Intercomparison Project; ACCMIP). An international group of scientists, including U.S. Department of Energy researchers at
Pacific Northwest and Lawrence Livermore National Laboratories, participated. The project consisted of a series of single time-slice experiments targeting long-term changes in atmospheric composition between 1850 and 2100. The focus was to document composition changes and the associated radiative forcing during
this period. The team studied 16 ACCMIP models in a wide range of horizontal and vertical resolutions, vertical extent, chemistry schemes, and interaction with radiation and clouds. While the groups specified anthropogenic and biomass burning emissions for all time slices in the ACCMIP protocol, they found that natural emissions are responsible for a significant range across models, especially in the case of ozone precursors. Model-to-model
comparisons of changes in temperature, specific humidity, and zonal wind between 1850 and 2000 and between 2000 and 2100 were mostly consistent; however, simulated meteorology for some outlier models
was different enough to significantly affect their atmospheric chemistry simulations. Isolation and comparison of the chemistry and aerosol effects on climate, as performed in this exercise, will be an important element of understanding overall climate change within the CMIP experiments.
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