Current heat waves are linked to climate change, scientists confirm

Climate change has made the extremely high temperatures in Europe more than twice as likely to occur, a new analysis has revealed. How do scientists calculate the link between extreme weather events and climate change?

Record-breaking temperatures of up to 39 degrees Celcius (102.2 degrees Fahrenheit) in Germany; out-of-control wildfires in Sweden and other typically cool northerly regions; and a toxic algae outbreak in the warmer than usual Baltic Sea in Poland — Europe is sweltering in the current heat wave.

Nature and Environment | 27.07.2018

With the extreme high temperatures continuing in most parts of Europe, people are asking: Is climate change to blame? 

Scientists say yes.

"Climate change has generally increased the odds of the current heat wave more than two-fold," said Geert Jan van Oldenborgh, a researcher at the Royal Netherlands Meteorological Institute.

He is part of World Weather Attribution (WWA), a network of scientists in six institutions established to provide near-real-time analysis of possible links between climate change and extreme weather events.

A WWA team has analyzed the current heat wave in northern Europe and presented preliminary results on Friday.

To stay cool in record-high temperatures, you can follow the example of this little boy: play at a fountain

How do scientists connect specific weather events to climate change?

Pinning down blame for complex weather events isn't straightforward, due to the numerous variables involved, from water temperature to air pressure.

But thanks to state-of-the-art climate models, scientists can now calculate the likelihood of individual extreme weather events having happened due to climate change.

Read more: Climate change and extreme weather: Science is proving the link

Like how epidemiologists link smoking to cancer, climate scientists work with statistical probability. 

"Smoking is never the only reason — but it increases the likelihood to develop cancer," Friederike Otto, researcher at the Oxford University's Environmental Change Institute and member of the WWA, told DW.

To determine the likelihood that an individual extreme weather event is caused by climate change, scientists estimate what the probability of a particular extreme event would be in the climate of today, versus in the climate of a world free of human-caused greenhouse gas emissions.

We've already warmed the globe by about 1 degree Celsius, compared to pre-industrial times.

By comparing the results of these two scenarios, scientists can attribute any differences in probability of the extreme event to human-caused climate change.

With this method, the WWA network has already shown that climate change made Hurricane Harvey in 2017 three times as likely to happen, the Lucifer heat wave that swept southern Europe in 2017 four times as likely to happen, and did not change the likelihood of the 2014 Sao Paolo drought taking place.

The banks of the river Rhine in Düsseldorf have cracked due to dryness

How did they calculate the probability of climate change causing the current heat wave?

The WWA researchers compared the currently high temperatures with historical records at seven weather stations in northern Europe — two in Finland and one each in Denmark, the Irish Republic, the Netherlands, Norway and Sweden.

The weather stations were selected for practical reasons. Current temperature data could be accessed in real time, and all of them had digitalized records extending back to the early 1900s.

For each year in the historical record, the scientists looked at the hottest consecutive three days. For 2018, they took the hottest three days of the year so far.

They then fed their the datainto  climate models, and compared the results of the world today with the world from the past when greenhouse gas emissions were much lower.

In the case of Copenhagen, the group found that a heat wave like the current one occurs every seven years in our current world. But in a world without manmade climate change, such a heat wave as this one occurs only every 35 years.

Even dogs seek refreshment during the current heat wave

"We can thus say climate change increased the likelihood of the event to occur by a factor of ten [in the case of Copenhagen]," Otto told DW.

Compiling all the results from the seven analyzed weather stations across Europe, the scientists found that the probability of such heat waves is overall twice as probable today than if human activities had not altered the climate.

The results are not yet peer-reviewed, because the WWA scientists are aiming to provide a quick analysis of current extreme weather events since public interest is high. They do plan to publish the results formally in a scientific journal, as they have done with previous analyses.

Why is it important to attribute specific extreme weather events to climate change?

Climate change is an abstract topic with abstract measures, for example the increase of the average global temperature on Earth.

But people don't experience average temperatures; they experience heavy rainfall (including flooding), heat waves, severe storms and droughts, researchers point out.

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"It's very important to provide illustrations of the effects of climate change," Robert Vautard, a senior scientist with France's Laboratory for Climate and Environment Sciences, told DW.

Only when we undestand what climate change looks like can we can prepare for it, he thinks. 

After the deadly heat wave in 2003, which resulted in the death of 15,000 people in France alone, the French government created an emergency plan to deal with future heat-related health problems. 

But experts believes their plan might already be outdated. 

"Our infrastructure and healthcare plans are based on heat waves and rainfall we have witnessed in the past. But we have to realize that the climate today is not the same it used to be, and it will be very different in the future," Vautard added.

Lawmakers in the United Kingdom, where unusual high temperatures of more than 30 degrees Celsius were recorded last week, face a similar fear.

They have warned that premature deaths from heat waves could triple by 2050, and call upon the government to develop a strategy to protect the health of the public.

Will we see more extreme weather events in the future?

Climate scientists almost universally agree: Yes.

"Extreme heat events like this one will become more frequent and more intense as the globe continues to warm," Andrew King, a researcher at the ARC Centre of Excellence for Climate Extremes at the University of Melbourne, told DW. 

"We know that heat waves and hot summers, like the infamous hot summer of 2003 in Europe, will very likely occur in most years, even under only 2 degrees Celsius of global warming," he added.

The Paris Climate Agreement seeks to limit global warming between 1.5 and 2 degrees Celsius but on our current track,we are moving towards 3 degrees warming.

The climate is not just getting hotter — it's getting less predictable.

Variability of extreme weather events will increase, confirmed climate scientist Otto. While we may one year see heat waves, the next year we could experience extreme rainfall. And the picture can look very different from location to location.

"The dangerous thing about climate change is that what we are not adapted to the changes," said Otto. 

Beyond the urgent current need to limit global warming to under 2 degrees Celsius, learning to adapt quickly to extreme weather events will be a great challenge for the future.

Soaring temperatures, wildfires scorch Europe

Europe strips off

Summer 2018 began as a welcome break from Europe's often-unpredictable weather, and people took advantage of the constantly warm temperatures to spend more time outside. The heat was especially a boon for pubs and bars where fans congregated to watch the soccer World Cup. But as temperatures climbed to up to 39 Celsius, the heat wave's negative effects began to be felt across the continent.

Soaring temperatures, wildfires scorch Europe

Racing against the clock

The high temperatures and low rainfall led to a sharp rise in wildfires across several European countries, including Sweden, where authorites were, at one stage, battling more than 50 blazes, some in the Arctic Circle. When German firefighters tackled a forest fire in Fichtenwalde, near Berlin, their operation was suddenly made more urgent by the discovery of unexploded World War II ammunition.

Soaring temperatures, wildfires scorch Europe

Paradise goes up in flames

Greece, meanwhile is counting the cost of its own devastating wildfire which last week left 86 people dead. The seaside village of Mati, just 30 kilometers (17 miles) from Athens, saw houses and land incinerated, while many people drowned after rushing into the sea or were burned alive while trying to escape in their cars.

Soaring temperatures, wildfires scorch Europe

Scorched earth as rivers start to run dry

Many of Europe's rivers and reservoirs experienced almost drought-like conditions after water levels dropped severely. Freight vessels that ply German sections of the River Rhine (pictured here in Düsseldorf) and Danube were ordered not to sail fully loaded. The Netherlands meanwhile closed several movable bridges after the metallic structures expanded so much that they couldn't be opened.

Soaring temperatures, wildfires scorch Europe

Heat makes great escape worse

As millions of Europeans hit roads, rail and air for their annual summer holidays, transport infrastructure struggled to cope. Eurotunnel passengers faced delays of up to five hours after the air conditioning units failed on trains. Some holidaymakers were forced to spend the night at Hanover airport after authorities canceled flights when one of the runways started to melt.

Soaring temperatures, wildfires scorch Europe

The coast is no escape

Poland shut scores of beaches along the Baltic Sea coast after the heat wave triggered a massive toxic algae bloom. German health officials, meanwhile, warned the elderly and others with weaker immune systems to avoid swimming in the Baltic Sea as the increased water temperature poses a danger from vibrio bacteria, which can cause severe illness.

Soaring temperatures, wildfires scorch Europe

Foods prices likely to rise

German farmers estimated the damage to crops from the heat wave could reach €1.4 billion and warned of higher supermarket prices. Other countries predicted the worst grain harvest in 25 years, as crops ripened much faster than expected and low rainfall produced a low yield. In Sweden, dairy farmers said they were being forced to slaughter some of their livestock.

Soaring temperatures, wildfires scorch Europe

Spray fountains keep Parisians cool

Until storms broke the intense heat on Friday evening, Parisians made use of the city's recreational facilities to keep cool, including water fountains around the Eiffel Tower. Despite being 3,324 pages long, France's infamous labor code doesn't mention a specific temperature that would force companies to shut down. But staff can't be punished if they stop work over fears for their health.

Soaring temperatures, wildfires scorch Europe

Dark clouds hint at end of hot spell

Parts of Europe experienced up to six weeks of uncomfortably hot weather. Forecasters predicted that the first storms would bring heavy rainfall to many areas this weekend. Thunder, rain and hail were reported in France and the UK on Friday evening, while the darkening clouds alerted the crowd at this cricket match just outside the English city of Leeds to prepare for a similar downpour.