Abstract

Persistent extremes atmospheric conditions over a season (classed as climate extremes by the IPCC ) are of particular importance as they can produce accumulated effects of greater impact than a single weather event. For example, the breakup of the Larsen B Ice Shelf occurred following a summer of persistent surface melt in 2002. From an ecosystem perspective, penguin breeding can be severely affected by persistent adverse conditions over a season. Our knowledge of the behaviour of extremes under climate change is poor due to both limited observations and a lack of necessary climate model simulations.

In this talk I will present the first multi-variate overview of the evolution of extreme seasons over Antarctica and the Southern Ocean during the 20th and 21st centuries, focussing on surface-air temperature, precipitation and near-surface wind. This has been made possible by the increasing availability of ‘large ensembles’ of climate model simulations, which involve running climate models many times and can be used to assess the behaviour of rare extreme events under climate change. Specifically, in this study available large ensemble datasets in the Coupled Model Intercomparison Phase 6 (CMIP6) archive were used to provide following medium-to-high radiative forcing scenarios.

The results show significant differences between simulated changes in background mean climate and changes in low (10th percentile) and high (90th percentile) extreme seasons. Regional winter warming is most pronounced for cold extremes. In summer, there are more pronounced increases in high extremes in precipitation and westerly wind during the ozone hole formation period (late 20th century), affecting coastal regions and, in particular, the Antarctic Peninsula. At midlatitudes, there is a reduction in the range of summer season wind extremes. Suggested mechanisms for these differences will be presented, in particular relating to sea ice retreat and westerly jet position.