Climate change

Increase in extreme weather events

Print edition : January 04, 2019

Flooding in a town in Bavaria. Photo: Getty Images/iStockphoto

ON the heels of the recent Climate Summit in Katowice, Poland, comes a study on the increasing rate of extreme weather events around the world as yet another warning on the need to find solutions to limit global warming to under 2°C. The paper by Jascha Lehmann and associates from the Potsdam Institute for Climate Impact Research, published in “Geophysical Research Letters”, finds that more and more rainfall extremes driven by climate change are observed in regions around the globe, triggering both record wet and dry spells.

Yet, there are big differences between regions: central and eastern United States, northern Europe and northern Asia have experienced heavy rainfall events that have led to severe floods in the recent past. In contrast, most African regions have seen an increased frequency of dry months. The study is the first to analyse systematically and quantify changes in record-breaking monthly rainfall events from all over the globe, on the basis of data from 50,000 weather stations worldwide.

The impacts on people’s livelihoods in the affected regions can be huge, ranging from flooded houses to endangered food security due to large-scale agricultural losses.The study finds that the U.S. has so far seen an increase of record wet months by more than 25 per cent in the eastern and central parts over the period 1980-2013. Argentina and bordering countries have experienced an increase of 32 per cent. In central and northern Europe, the increase is between 19 and 37 per cent. In the Asian part of Russia, the increase is around 20 per cent, while South-East Asia shows an increase of about 10 per cent.

The scientists ran strict tests for the statistical significance of the observed changes. “Approximately one out of three record-dry months in this regions would not have occurred without long-term climate change,” pointed out co-author Dim Coumou from the Institute for Environmental Studies (IVM) at Vrije Universiteit Amsterdam. “A central conclusion from our study is that, generally, land regions in the tropics and subtropics have seen more dry records, and the northern mid- to high-latitudes more wet records—this largely fits the patterns that scientists expect from human-caused climate change.”

The scientists compared wet and dry rainfall extremes to the number of extremes that would be expected in a climate without long-term changes. “Normally, record weather events occur by chance and we know how many would happen in a climate without warming,” explained Lehmann. “It’s like throwing a dice: on average, one out of six times you get a six. But by injecting huge amounts of greenhouse gases into the atmosphere, humankind has loaded the dice. In many regions, we throw sixes much more often with severe impacts for society and the environment.”

“It is worrying that we see significant increases of such extremes already at just one degree global warming,” added Lehmann. “If they [the nations] do not agree on solutions to limit warming to well below 2 degrees, we’re headed for 3-4 degrees within this century. Physics tells us that this would boost rainfall extremes even further.”