What to Expect
The Community Earth System Model “initial-condition Large Ensemble” has been widely used to disentangle forced climate change from internal climate variability at regional scales. Here,we introduce a complementary set of experiments to study the individual roles of greenhouse gases and anthropogenic aerosols in the evolution of multi-decadal trends since 1920, with a focus on large-scale patterns of precipitation and sea surface temperature. Aerosols from industrial sources and biomass burning are the primary driver of forced trends before the mid-1970s, with greenhouse gases dominating thereafter. During the first half of the 20th century, aerosols cause an inter-hemispheric shift in climate associated with cooling over northern latitudes. This pattern evolves into an equatorially-symmetric structure during the second half of the 20th century when trends in aerosol emissions are predominantly located in the tropics. This equatorially-symmetric structure is similar to that induced by greenhouse gases, albeit of opposite sign, and results in a relative minimum in forced trend amplitudes. Internal variability limits the detectability of aerosol and greenhouse gas forced trend patterns in individual realizations and in observations throughout the historical period.
Clara Deser studies global climate variability and climate change in observations and models, with an emphasis on interactions among the atmosphere, ocean, and sea ice. Recent projects include the role of internal variability in regional climate change, the effects of projected Arctic sea ice loss on global climate, asymmetries between El Nino and La Nina, and Pacific decadal variability.
In addition to serving as head of the Climate Analysis Section, she co-chairs the CESM Climate Variability and Change Working Group, and co-leads a number of community projects including the CESM1 Large Ensemble Project, CESM1 Single Forcing Large Ensemble Project, the Climate Data Guide, Climate Variability Diagnostics Package, US CLIVAR Working Group on Large Ensembles, and the WCRP Polar Amplification Model Intercomparison Project.
She is a Fellow of the American Geophysical Union and the American Meteorological Society. Clara received her Ph.D in Atmospheric Sciences from the University of Washington in 1989, and her B.S. from the Massachusetts Institute of Technology in 1982.