Summer weather extremes, such as heatwaves, drought and rainy periods, may increase in duration in the Northern Hemisphere mid-latitudes if global temperatures rise by 2 °C above pre-industrial levels, reports a paper published in Nature Climate Change.

With global warming, the frequency of extreme heat and rainfall events worldwide has increased and this trend is expected to continue with future warming. Rises in extreme heat and rainfall can have impacts on human health and agriculture, and on the environment, including an increased risk of wildfires. Extreme weather events are often measured in terms of intensity or frequency, but often it is the duration, or persistence, of events that leads to the most severe impacts.

Peter Pfleiderer and colleagues present a multi-model analysis of the persistence of local weather conditions in the Northern Hemisphere mid-latitudes. They suggest that if temperatures were to rise by 2 °C relative to pre-industrial levels, hot weather periods of longer than two weeks could increase by around 4％ relative to the recent past across the mid-latitudes. Eastern North America could see persistent hot and dry spells rise by up to 20％. The authors also suggest that heavy rainfall lasting for one week or more, which can lead to flooding, could increase by 26％ on average for the mid-latitudes under a 2 °C scenario. When considering projected warming of 1.5 °C, the authors found these increases were largely avoided.