A new study has analysed the human contribution to the record-breaking heat wave which struck Western Europe and Scandinavia at the end of July 2019 – just a month after the extreme heat that took place in the last week of June 2019

The study Human contribution to the record-breaking July 2019 heat wave in Western Europe, published by World Weather Attribution,assessed how human-induced climate change has altered the likelihood and intensity of the July event or similar events.

The Environmental Change Institute, University of Oxford, the Royal Netherlands Meteorological Institute (KNMI) and Red Cross Red Crescent Climate Centre are all partners in the World Weather Attribution group.

In June, new all-time records were set in multiple places across Western Europe. In July, records were broken again, albeit in different areas. Again, the role of climate change in producing such high-amplitude events was questioned.

The study used a large number of climate simulations that were available at the time of study and combined information from both long series of observations and climate model simulations. The approach used was in order to obtain best estimates of changes in probability and intensity of an event like (or more severe than) the observed July extreme temperatures in Western Europe attributable to human-induced climate change.

Key findings

A second record-breaking heat wave of 3-4 days took place in Western Europe in the last week of July 2019, with temperatures exceeding 40 degrees in many countries including Belgium and the Netherlands where temperatures above 40°C were recorded for the first time.

In the U.K. the event was shorter lived (1-2 days), yet a new historical daily maximum temperature was recorded exceeding the previous record set during the hazardous August 2003 heatwave.

In contrast to other heat waves that have been attributed in Western Europe before, World Weather Attribution said the July heat was also a rare event in today’s climate in France and the Netherlands.

There, the observed temperatures, averaged over 3 days, were estimated to have a 50-year to 150-year return period in the current climate. Note that return periods of temperatures vary between different measures and locations are therefore highly uncertain.

Combining information from models and observations, the study found that such heatwaves in France and the Netherlands would have had return periods that are about a hundred times higher (at least 10 times) without climate change. Over France and the Netherlands, such temperatures would have had extremely little chance to occur without human influence on climate (return periods higher than ~1000 years).

In the U.K. and Germany, the event is less rare (estimated return periods around 10-30 years in the current climate) and the likelihood is about 10 times higher (at least 3 times) due to climate change. Such an event would have had return periods of from a few tens to a few hundreds of years without climate change.

In all locations an event like the observed would have been 1.5 to 3 ºC cooler in an unchanged climate.

July 2019 heatwave would have been extremely unlikely without climate change

World Weather Attribution concludes:

“It is noteworthy that every heatwave analysed so far in Europe in recent years (2003, 2010, 2015, 2017, 2018, June 2019, this study) was found to be made much more likely and more intense due to human-induced climate change.”

“How much more depends very strongly on the event definition: location, season, intensity and duration. The July 2019 heatwave was so extreme over continental Western Europe that the observed magnitudes would have been extremely unlikely without climate change.”

The study was made possible thanks to a strong international collaboration between several institutes and organisations in Europe, including Red Cross/Red Crescent, Royal Netherlands Meteorological Institute, Météo-France, UK Met Office and the Radcliffe Meteorological Station in Oxford.

Click here to download the study in full