Cloud and aerosol processes and their influence on the coupled climate system, 2) polar climate including mechanisms for recent and projected Arctic sea ice loss, 3) evaluation and improvement of climate models using data assimilation and satellite observations (especially CloudSat and CALIPSO), 4) communicating climate change science.
Polar climate change and variability
I joined CIRES/CU-Boulder in January 2014. Two Ph.D. students, Vineel Yettella and Ariel Morrison, start their research with me this summer. My group connects global coupled climate modeling with cloud, precipitation, and sea ice observations to understand the processes controlling polar climate change and variability. Working at the nexus of observations and modeling is challenging but rewarding. Here, I’ll describe two recent projects.
During the last year, I co-led a large modeling experiment using a global coupled climate model: the Community Earth System Model (CESM). The experiment was designed to enable community assessment of climate change in the presence of internal climate variability. The core simulations replay 1920 to 2080 30 times under historical and large future greenhouse gas forcing. The ensemble members differ only in their 1920 atmospheric air temperature initialization. Early results document the surprisingly important and at times dominant influence of internal climate variability on climate trajectories. Nature is an ensemble member, not the ensemble mean. Accelerations and pauses in global warming occur. Sea ice loss is prevalent, but the loss amount varies from member to member. Now I am analyzing climate variables influencing Greenland Ice Sheet melt in the ensemble (see figure).
The Southern Ocean is the cloudiest place on Earth. Climate models have large cloud and radiation biases and interesting cloud-climate feedbacks over the Southern Ocean. As a result, I am obsessed with the intriguing cloud structures found there (see satellite image). In a 2014 Geophysical Research Letters paper, we found, using CESM, that the radiatively important clouds are low-level, liquid clouds. Interestingly, these clouds respond primarily to thermodynamics (warming and stability changes), not dynamics (jet variability and jet shifts), under climate change scenarios. We are now looking into reducing Southern Ocean radiation biases in CESM by improving the match between observed and modeled cloud supercooled liquid water. We anticipate our improvements will have both local and remote impacts.
The poorly observed and rapidly changing polar regions present many exciting research opportunities of global importance. The Kay Group has plenty to keep us busy.