2019 Southern Hemisphere SSW was not a Result of Climate Change

Abstract:

Sudden Stratospheric Warmings (SSWs) are historically rare in the Southern Hemisphere (SH). The occurrence of two events (2002 and 2019) within two decades then warrants the question whether greenhouse gas (GHG) forcing might be the reason for this, and whether we might see more SSWs in the SH. Analysing nearly 10k years of fully stratosphere-resolving coupled climate model simulations and CMIP5/6 data, we show that in present-day conditions, one SSW every two decades should not be viewed as unusual. We further find that increasing GHGs greatly decrease the probability of occurrence of SSWs and did not cause the 2019 event. Given the expected increases in GHGs, we postulate that there will not be a third event in this century.