Climate change made French heatwave 'more likely' in hottest June ever

Marlowe HOOD, Patrick GALEY, AFP Yahoo News 3 Jul 19;

Paris (AFP) - The record-breaking heatwave that gripped France last week was made at least five times more likely by climate change, scientists said Tuesday as other data showed that last month was the hottest June worldwide in history.

Compared to weather stretching back more than a century, the three-day temperature peak from June 26-28 in France was four degrees Celsius (7.2 degrees Fahrenheit) warmer than an equally rare June heatwave would have been in 1900, the World Weather Attribution (WWA) team told journalists in a briefing.

Global readings, meanwhile, taken by the EU's Copernicus Climate Change Service (C3S) showed European temperatures were around 2C hotter than normal, and globally Earth was 0.1C hotter than the previous June record.

The heatwave last week smashed national records for the hottest single day as scorching weather spread across Europe from the Sahara. It was so intense that temperatures were as much as 10C higher than normal across France, Germany, northern Spain and Italy, C3S said.

Global warming probably amplified France's devastating hot spell by far more than five times, said Friederike Otto, acting director of the Environmental Change Institute at the University of Oxford.

"Models are very good at representing large-scale seasonal changes in temperatures," she explained.

"On localised scales, climate models tend to underestimate the increase in temperature."

- 'Likely role much higher' -

The findings, presented as a report and to be published in a peer-reviewed journal, focused on metropolitan France and the southern city of Toulouse, where climate statisticians were coincidentally meeting during the heatwave.

Based purely on temperature records, extreme scorchers like the one last week are now 100 times more likely than in 1900, said Geert Jan van Oldenborgh, a senior researcher at the Royal Netherlands Meteorological Institute and co-author of the new report.

"But we are unable to say that this is just because of climate change," he said.

Air pollution, the "urban heat island" effect, soil moisture, cloud cover and a host of other factors can also affect the intensity of heatwaves.

And models designed to work on a different scale are consistently "biased" such that they underestimate temperature peaks.

"Given what we know about the observation data and the biases of the models, this is our most conservative estimate as to the contribution of climate change," Otto told AFP.

"The likely role is much higher."

- 3C hotter than average -

Merging satellite data with historic temperature charts, the Copernicus team found June 2019 was 3C hotter across Europe than the baseline average between 1850-1900.

"Our data show that the temperatures over the southwestern region of Europe during the last week of June were unusually high," said Jean-Noel Thepaut, head of C3S.

"Although this was exceptional, we are likely to see more of these events in the future due to climate change."

France, Italy, Spain and some central European nations all posted all-time temperatures peaks, with dozens of deaths attributed to the week-long heatwave.

A 2003 heatwave in France claimed at least 15,000 lives, according to government figures.

Martha Vogel, a climate researcher at the Swiss Federal Institute of Technology in Zurich who was involved in the WWA research, said it was "virtually certain" that Europe's heatwave last year could not have occurred without climate change.

Earth has already warmed by 1C since pre-industrial levels. Vogel and the team in a study published last month found that just 2C of warming -- levels aimed for in the Paris climate deal -- would see a 2018-style heatwave happen every year.

"The five hottest European summers -- 2018, 2010, 2003, 2016, 2002 -- were all in this century," she told AFP.

Climate change made European heatwave at least five times likelier
Searing heat shows crisis is ‘here and now’, say scientists, and worse than predicted
Damian Carrington The Guardian 2 Jul 19;

The record-breaking heatwave that struck France and other European nations in June was made at least five – and possibly 100 – times more likely by climate change, scientists have calculated.

Such heatwaves are also about 4C hotter than a century ago, the researchers say. Furthermore, the heatwaves hitting Europe are more frequent and more severe than climate models have predicted.

Last month was the hottest June since 1880, both in Europe and around the world, according to separate data released on Tuesday by the EU’s Copernicus Climate Change Service. In Europe the temperature was 3C above the June average a century ago, and globally it was more than 1C higher.

The European heatwave broke temperature records at many locations in France, Switzerland, Austria, Germany and Spain. In France it was broken by more than 1.5C on 28 June, with 45.9C recorded near the city of Nîmes.

The searing heat led to wildfires in Spain and Germany, and widespread disruption across the continent. It is inevitable that the heatwave will have caused many premature deaths, particularly as it occurred outside the usual holiday months when people are more able to take shelter. But these figures take time to compile. The heatwave of 2003 caused more than 70,000 premature deaths across Europe.

Dr Friederike Otto, of the University of Oxford, one of the scientists behind the new analysis, said: “This is a strong reminder again that climate change is happening here and now. It is not a problem for our kids only.”

Another team member, Geert Jan van Oldenborgh, of the Royal Netherlands Meteorological Institute, said: “If the observed trend in heatwaves continues, [even] at the Paris goal of 2C of warming a heatwave like this will be the norm in June. Both observations and models show a strong trend towards stronger heatwaves. However, the observed trend is stronger than the modelled one, and we do not yet know why.”

Global heating caused by the carbon emissions from burning fossil fuels and other human activities means heatwaves are becoming more probable and severe, a key part of the climate crisis. “Attribution” studies such as the new analysis estimate how much more likely and severe they are. The unprecedented heat and wildfires across the northern hemisphere in 2018 “could not have occurred without human-induced climate change”, a separate study published in June found.

The latest analysis examined the hottest three-day period of last month’s heatwave in France – 26 to 28 June. The scientists used average daily temperatures, as these are a better indicator of the effects on health than maximum or minimum temperatures. The average across those three days and nights was 27.5C.

The researchers, many of whom happened to be at a conference on extreme events and climate change in Toulouse, then used temperature records stretching back to 1901 to assess the probability of a heatwave last month and in the past. They also examined climate change models to assess the impact of global heating.

Global heating caused by human activities made the French heatwave at least five times more likely, said Otto, based on combining the observations and climate models. Analysis of the observations alone indicated the heatwave was at least 10 times more likely than a century ago, and potentially 100 times.

However, these bigger increases in probability may result in part from changes in land use, soil moisture and irrigation, the growth of towns and cities, and air pollution, all of which can affect temperature.

There have been more than 230 attribution studies to date around the world and these have found that 95% of heatwaves were made more more likely or worse by climate change. For droughts, 65% were definitely affected climate change, while the figure for floods was 57%. The analysis of France is not yet peer-reviewed but was done using similar methodologies.

“We knew June was hot in Europe, but [the Copernicus data for June] show that temperature records haven’t just been broken – they have been obliterated,” said Prof Hannah Cloke, of the University of Reading. “It is the hottest June on record in Europe by a country mile. As heatwaves become more common, we will have to change the way we live to cope with them.”

Nick Watts, the executive director of the Lancet Countdown on health and climate change, said heatwaves affected elderly people and those with pre-existing conditions most.

“The effects will be felt in the form of exacerbated heart disease and heat-related illness, spikes in hospital admissions and premature death, and increased pressure on health services,” he said. “It is clear that health services and local authorities require increased funding if they are to meet the rising threat of climate change to health.”