Climate change made European heatwave at least five times likelier


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 the climate crisis, scientists have calculated.

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

The heatwave broke temperature records at many locations in France, Switzerland, Austria, Germany and Spain. The all-time temperature record for France was broken by more than 1.5C on 28 June, with a new high of 45.9°C 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 major European heatwave of 2003 caused more than 70,000 premature deaths.

Greenhouse gas emissions from burning fossil fuels, forest destruction and other human activities are trapping heat and putting more energy into the climate system. 

Hotter air means heatwaves are much more likely. For example, scientists now say the unprecedented heat and wildfires across the northern hemisphere in 2018 “could not have occurred without human-induced climate change”. In Australia, the scorching summer of 2016-17 in New South Wales was made at least 50 times more likely by global heating, linking it directly to climate change.

Hotter air can also carry more water vapour, meaning more intense rain and more flooding. 

Another important factor in the northern hemisphere is the impact of changes in the Arctic. The polar region is heating more rapidly, reducing the temperature difference with lower latitudes. There is strong evidence that this is weakening the planetary waves (including the jet stream) that normally meander over Europe, Asia and North America.

When these waves stall, weather gets fixed over regions and becomes extreme. This has been linked to past floods in Pakistan, heatwaves in Russia and drought in California. 

Most of the planet’s trapped heat goes into the oceans and rising sea temperatures mean more energy for hurricanes and typhoons. Record-breaking cyclones hit Mozambique in March and April. The deluge delivered in the US by Hurricane Harvey in 2017 was made three times more likely by climate change. Rising sea level also means storms cause more coastal damage.

Global heating does not influence all extreme weather – natural variability still exists. Carbon Brief analysed more than 230 studies and found 95% of heatwaves were made more likely or worse by climate change. For droughts, 65% were definitely affected by our hotter world, while the figure for floods was 57%. It is now undeniable that global heating is causing more extreme weather.

Friederike Otto, at the University of Oxford, UK, 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.”

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Geert Jan van Oldenborgh at the Royal Netherlands Meteorological Institute, another team member, 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 being made more likely 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. A separate study published earlier in June looking at the unprecedented heat and wildfires across the northern hemisphere in 2018 found it “could not have occurred without human-induced climate change”.

The new work looked at the hottest three-day period in France – 26 to 28 June – which was at the centre of the recent heatwave. The scientists used average daily temperatures, as these are a better indicator of impacts on health than maximum or minimum temperatures. The average temperature in France across those three days and nights was 27.5C.

People cool down in the fountains near the Eiffel Tower in Paris during the June heatwave.



People cool down in the fountains near the Eiffel Tower in Paris during the June heatwave. Photograph: Anadolu Agency/Getty Images

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 how likely the heatwave was today, and how likely in the past. They also examined climate change models to assess the impact of global heating.

The French heatwave was made at least five times more likely due to the global heating caused by human activities, said Otto, based on combining the observations and climate models. But analysis of the observations alone indicate 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 95% of heatwaves were made more more likely or worse by climate change. For droughts, 65% were definitely affected by our hotter world, while the figure for floods was 57%. The analysis of France is not yet peer-reviewed but was done using similar methodologies.

Nick Watts, executive director of the Lancet Countdown on Health and Climate Change, said heatwaves affected the elderly and those with pre-existing conditions the 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.”



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