Climate Change Plays Significant Role in European Heat Wave

The ongoing heat wave dominating a large swath of Europe is being exacerbated by climate change, according to a new analysis by a team of international scientists using both observational data and climate models.

It is widely accepted that climate change will increase the frequency, intensity and duration of heat waves (Meehl and Tebaldi, 2004). In 2004, a paper published in Nature showed that climate change had at least doubled the risk of the record-breaking 2003 European summer heat wave that is believed to have killed more than 70,000 people.

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In this case, as part of the world weather attribution project, our partners at Climate Central convened an international team of scientists from Oxford University, KNMI, Red Cross Red Crescent Climate Centre, along with regional partners from CNRS and MeteoSwiss in order to assess the potential role of global warming on a specific heat event – not just a record hot summer. The team defined the specific heat event for selected European cities (De Bilt, Madrid, Mannheim, Paris, and Zurich) using a reference of 3-day maximum temperature.

Using our large weather@home computing network, we simulated the likelihood of seeing days as hot as  as those Europe is experiencing now. At the same time, we also simulated a summer where there is no human-influenced climate change. Comparing those two “worlds” we found that in the 5 cities analyzed, average 3-day high temperatures  like those currently being observed and forecast  have been made at least twice as likely in the world with climate change.

“The results we currently have should be viewed as preliminary,” said Friederike Otto, “because the observed sea surface temperatures are not yet available for this summer, we have simulated the summer of 2014 as a proxy. However, because it is well understood that the influence of the exact sea surface temperatures in Europe is small compared to the overall effect of global warming, these numbers provide a good first step towards answering the climate question.”

Using a combination of observed and forecast data, scientists from the team at KNMI computed the annual maximum of 3-day maximum temperature (observations up to July 1, forecasts up to July 5).

“There is a strong upward trend in 3-day maximum temperatures over the area affected by this heat wave,” said Geert Jan van Oldenborgh, a climate scientist at KNMI. “The trend is clear both in station data and in reanalysis data.” Because the heat wave is ongoing, the analysis partly relies on forecasts for the next few days. A statistical analysis of the observations shows that the probability of observing such a heat wave has more than doubled over the past 37 years in most of the affected region. In the selected cities the increase is even stronger.

The methodology used in these two approaches is drawn from peer reviewed literature. For more details on each approach please refer to the Methodology outlined for a previous analysis on the record heat in Europe in 2014.

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