| Summary: | Projected 21 st century changes in Antarctic climate predicted to have major impacts on physical and ecological systems, with implications globally. With regard to impacts, the magnitude of time-mean climate responses compared to internal year-to-year variability is key, as it provides a measure of the extent to which mean responses may shift the system outside the range of conditions experienced in the past. This is highly relevant for estimating future occurrence of extreme years or seasons. Maps of projected time mean responses and the expected ranges about these responses associated with year-to-year variability will be presented at different time points through the 21 st century; 2020, 2050 and 2080. These are calculated based on output from many CMIP6 climate models following a range of forcing scenarios. Results show that even on a local scale, mean responses in temperature emerge rapidly from internal variability and by 2050 are already comparable to the 10-90 th percentile range of internal variability over many parts of Antarctica. As a consequence, an unusually warm year in present day would be a typical year in 2050. In contrast to temperature, for precipitation and surface westerly wind, mean responses generally remain within year-to-year internal variability through the whole 20 th century and across a range of forcing scenarios. However, the Antarctic Peninsula is a key exception, where projected increases in time mean westerlies and precipitation rate approach the 10 th -90 th percentile range in year-to-year variability. Implications of sea ice decline and jet shift for future change in year-to-year variability will be discussed.
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