A heatwave in 2018 left the riverbed of the Rhine in Germany parched PATRIK STOLLARZ/AFP/Getty Images

Summer extremes of heat and rain are likely to last longer in Europe, North America and Asia if the world warms by more than 2°C, with serious effects for agriculture and human health.

Climate change is expected to bring more frequent and intense extreme weather events. But how persistent those episodes will be, such as the European summer heatwave in 2018, is not so well understood.

Carl-Friedrich Schleussner at Climate Analytics in Germany and his colleagues modelled the persistence of extreme events across the northern hemisphere if temperatures rise by more than 2°C, the upper limit governments are targeting. They found that countries across the northern hemisphere in summer will, on average, face a 26 per cent greater probability of heavy rainfall lasting for at least a week. That much rain in summer can lead to devastating floods, such as those that hit France and Germany in 2016.


“The main message is that basically we will not just get more warming, but… [we] are changing the weather. It is relevant for farmers, ecosystems, how we build cities,” says Schleussner. Heatwaves and floods have hit US states throughout the summer of 2019, and temperatures in India and China have broken records in 2018 and 2019, reaching 50°C in India in June 2019 and killing dozens of people.

The northern hemisphere faces the prospect of more persistent heatwaves, with the probability of fortnight-long warm periods increasing by 4 per cent on average. The weakening jet stream, driven by a warming Arctic, is one factor behind the increased persistence.

Geert Jan van Oldenborgh at the Royal Netherlands Meteorological Institute says looking at persistence is useful because “society is much more vulnerable to extended periods of extremes.”

The good news is the increased likelihood of these extremes can be almost entirely avoided – if temperature rises are kept to 1.5°C, the Paris climate deal’s tougher goal. Hannah Cloke at Reading University says: “this is a useful modelling experiment and there is some encouraging evidence here for making the case that we can make a difference by limiting global warming and taking action now.”

The bad news is the world is on track for more than 3°C, which Schleussner says would likely bring “much bigger changes in persistence”.

Journal reference: Nature Climate Change, DOI: 10.1038/s41558-019-0555-0