At the end of July, temperatures of over 40 degrees were measured in the Netherlands. NU.nl spoke with an expert who investigated the causes. Even in the current climate, this heat was very extreme, but that will change if the warming continues.

Geert Jan van Oldenborgh of the KNMI is part of an international team that conducted a so-called 'attribution study' immediately after the heat wave. In such studies, climate scientists try to trace the causes of specific extreme events. The studies answer the question to what extent weather extremes are influenced by global climate change.

"For such a study, we first have to analyze the trend in observations," explains Van Oldenborgh. "Climate models that can simulate weather extremes then calculate the influence of greenhouse gases."

The conclusion came out at the beginning of August: climate change played a major role in the heat wave in Europe at the end of July. For example, without global warming it would be about fifty times as unlikely that the heat records observed in England would have been reached.

And the chance of the extreme heat in the Netherlands and Belgium, where temperatures above 40 degrees were measured for the first time, has even increased by a hundred times due to current climate change. In the old climate, this extreme heat wave was "virtually impossible", the KNMI writes.

See also: Climate change: How much warmer does it actually get?

40 degrees also very rare in today's climate

That makes such a summer heat definitely not 'the new normal'. Even in the current, already warmed up climate, temperatures in the Netherlands above 40 degrees are extremely rare: the annual chance of repeating the temperatures measured in July in the current climate is only 1 to 2 percent, we reported earlier based on the study from World Weather Attribution.

That will be a different story if global warming continues. Van Oldenborgh: "It may be an open door, but the chance of heat waves increases as the earth warms up."

In a century and a half, the world average has become slightly more than 1 degree warmer. In the Netherlands it goes faster than average, it is now 1.7 degrees warmer than in the so-called 'pre-industrial climate', when the CO2 concentration was about a third lower than today.

End of July in Greenland: European heat wave led to the melting of record quantities of ice. (Photo: Reuters)

Will extreme heat waves become normal in the future?

That warming is accelerating. On average, the world is currently about 0.2 degrees warmer every ten years, and if global emissions continue to grow unhindered this century, global warming now observed by the end of the century can be around five times as high.

If, on the other hand, greenhouse gas emissions are strongly reduced, most of this future warming can still be prevented: the aim of the Paris agreement is to limit warming to 2 degrees, and preferably 1.5 degrees.

Even in this most ambitious scenario, the chance of extreme heat waves is increasing rapidly, Van Oldenborgh says: "With 1.5 degrees global warming, the ambitious goal of the Paris agreement, the chance is already around 15 percent per year. With 2 degrees of warming this increases to around 25 percent, so the past heat wave occurs on average once every four years. "

"And if the world average temperature goes up even further, to 3 or 4 degrees or more, the summer heat of 2019 will actually become a normal summer and a new outer category of even more extreme heat waves will emerge."

Other links heat waves and climate change

The European heat wave later moved to Greenland and led to the melting of a record amount of ice. Other climate scientists pointed out in June that the risk of heat waves in Europe may increase further due to the melting of the Arctic ice.

Researchers at Wageningen University also reported a link between recent heat waves in the Netherlands and drought in France and Spain on Tuesday. Dehydrated areas can transport hot air over longer distances, without significantly cooling.

Starting today, we are putting extra time and energy into the subject of climate and the booklet is on the front page of NU.nl every week. Wednesday was originally the day that the Werk section was featured on the front page. What happens with that? Nothing: On Wednesday you will find Climate and Work on our site and app.

What does the rest of the week look like now?

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