Projections of cold air outbreaks in CMIP6 earth system models

Historical and future simulated temperature data from five climate models in the Coupled Model Intercomparing Project Phase 6 (CMIP6) are used to understand how climate change might alter cold air outbreaks (CAOs) in the future. Three different shared socioeconomic pathways (SSPs), SSP126, SSP245, and SSP585, are examined to identify potential fluctuations in CAOs across the globe between 2015 and 2054. Though CAOs may remain persistent or even increase in some regions through 2040, all five climate models show CAOs disappearing by 2054 based on current climate percentiles. Climate models were able to accurately simulate the spatial distribution and trends of historical CAOs, but there were large errors in the simulated interannual frequency of CAOs in the North Atlantic and North Pacific. Fluctuations in complex processes, such as Atlantic Meridional Overturning Circulation, may be contributing to each model's inability to simulate historical CAOs in these regions. Plain language summary Cold air outbreaks (CAOs) are extreme events that can have large, negative impacts on society. Because of these impacts, it is important to understand how climate change might alter CAOs in the future. Three future scenarios from five different climate models are examined to see where CAOs might change the most between 2015 and 2054. While changes in CAOs may be small for some regions through 2040, all the climate models show CAOs disappearing, relative to the historically defined criteria, by 2054. Where the climate models did a good job simulating historical CAOs, like in North America, we have confidence that future projections are relatively accurate. Where the models did poorly at simulating historical CAOs, like the North Atlantic and North Pacific, we have less confidence in future projections. More work needs to be done to understand the complex processes that lead to these errors.