Antarctic Cryospheric Change: Mechanisms and Feedback on Climate
DESCRIPTION: This project will investigate some of the physical mechanisms driving past and future Antarctic cryospheric change, and the resulting feedbacks on climate. The project has three objectives. First, the cryospheric response to changes in absorbed solar radiation (ASR) at high southern latitudes will be assessed. This will be investigated both within the context of climate model biases in present-day climatological mean ASR, and in terms of multidecadal ASR trends due to stratospheric ozone depletion and recovery. Model biases in Antarctic ASR will be correlated with the simulated climatological mean and interannual standard deviation of sea-ice concentration, sea-ice thickness, and surface snow/ice sublimation and melt. Additionally, multidecadal trends in Antarctic sea ice due to ozone depletion and recovery will be quantified using a series of simulations with the Community Earth System Model-Whole Atmosphere Community Climate Model (CESM-WACCM, or simply WACCM). The impact of ASR trends on these sea-ice trends will be assessed and compared with the impacts of other physical mechanisms (e.g., changes in Southern Ocean overturning circulation). The second objective of the project is to quantify the effect of ozone depletion and recovery on the mass balance of the Antarctic ice sheet. This will be accomplished both by analyzing the WACCM simulated surface mass balance, and by performing a series of sensitivity simulations with a stand-alone ice sheet model (the Ice Sheet System Model, or ISSM) forced by WACCM output. The ozone effect on Antarctic mass balance will be compared with the effect of increasing greenhouse gases, and both effects will be translated into global sea-level rise equivalent. The third and final objective is to determine the atmospheric response to Antarctic sea-ice changes. This will be achieved by running WACCM with prescribed sea surface temperatures and sea-ice concentrations in order to examine the impacts of different sea-ice anomaly patterns. Sea-ice anomalies associated with Antarctic Dipole variability, the observed trend during the satellite era, and future climate change will all be considered. The simulated response to these sea-ice changes will be evaluated in terms of changes in the mean and variability of Antarctic temperature and precipitation, atmospheric circulation (e.g., the Southern Annular Mode), and stratospheric ozone.
OUTCOMES: This project will enhance understanding of cryosphere-climate interactions in the Antarctic, thereby allowing for attribution of recently observed changes, and for improved quantification of the physical drivers of model-simulated future climate change. By achieving a better understanding of the causes and consequences of climate model biases, the project will also produce information that will be useful for improving models and thus refining future projections. The proposed work will produce the first quantitative estimates of Antarctic dynamic mass loss due to stratospheric ozone depletion and recovery, with great relevance for understanding past and future trajectories of global sea-level rise. Finally, the climate feedback from Antarctic sea-ice changes will be investigated in the most systematic way to date.