European summer heatwaves ten times more likely with climate change

Climate change is raising the odds of summer heatwaves in Europe by a factor of 10, according to new research from the Met Office. Over the past 10 to 15 years, the likelihood of a ‘very hot’ summer has risen – from once every 50 years to once every five years.

As the frequency of heatwaves increases, so do risks to human health. Improving resilience to high temperatures is critical to avoiding deaths caused by extended periods of hot weather, the authors say.

A record heatwave

The summer of 2003 was  the hottest ever recorded for central and western Europe, with average temperatures in many countries as much as five degrees higher than usual.

Studies show  at least 70,000 people died as a result of the extreme high temperatures. In August alone, France recorded over 15,000 more deaths than expected for that time of year, a 37 per cent rise in the death rate. The same month also saw almost 2,000 extra deaths across England and Wales.

To see how climate change is affecting the likelihood of heatwaves and other extreme events, researchers carry out  attribution studies. These identify the  fingerprints of human influence on observed changes in temperature, rainfall, and other climate parameters.

The heatwave was the first extreme weather event to be attributed to the human influence on the climate, with research suggesting it was made  more than twice as likely because of climate change.

Now a new study, published in Nature Climate Change, finds that recent warming means a similar heatwave is even more likely. The increasing impact of humans on the climate means the risk of ‘extremely hot’ summers is now ten times greater than when the 2003 European heatwave struck.

Very hot summers every five years

In the new study, Met Office researchers ran their climate models twice: first with both natural climate fluctuations and manmade warming included, and secondly with only natural influences on the climate. They compared the results to see how rising temperatures have altered the odds of heatwaves in Europe.

You can see in the left-hand chart below how close the model simulations that include manmade warming (black line) are to actual recorded summer temperatures (red line). By contrast, modelled summer temperatures from a world where there’s no human influence on the climate don’t match up well with what scientists are seeing.

This shows summer temperatures can’t be explained by natural variability alone, and climate change is playing a role, the paper explains.

Model simulations of European summer average temperatures with climate change (left-hand chart) and without climate change (right-hand chart). Red lines show actual temperatures relative to the long-term average.

The two small horizontal lines on the charts show the average European summer temperature from 1990-1999 (green line) and 2003-2012 (black line). The difference between the two periods means that average temperatures have risen, pushing up the likelihood of temperature extremes. While a heatwave used to happen once every 50 years, we’re now likely to see one every five years, the study concludes.

We can expect an ‘extremely hot’ summer like 2003 to happen once every century, where previously it would only be expected to occur once a millenium, the paper adds.

Heatwaves to be ‘very common’ in the future

The researchers also examine how the odds of summer heatwaves in Europe are likely to change in the future as temperatures continue to rise.

Heatwaves such as 2003 will become “very common” by the 2040s under all emissions pathways used by the Intergovernmental Panel on Climate Change. If greenhouse gas emissions continue to rise as they are currently, a heatwave on par with the 2003 event could even be considered “extremely cold” by the end of the century, the study suggests.

This means we might get a different perspective on what a ‘hot’ summer really means. As Dr Nikos Christidis, lead author of the study, tells us:

“[A]s summer temperatures continue to increase, the perception of extremely hot summers is set to change drastically over the next few decades.”

Given the consequences of the 2003 heatwave, increasing society’s resilience to such events should be of paramount importance to adaptation planners, the paper concludes.

Main image: Beach of the Cote d’Azur with tourists, sunbeds and umbrellas on the hot summer day. Credit: LiliGraphie/Shutterstock.com.