By Andrew Freedman From Mashable

In July and August 2003, a high pressure area settled in for an extended, unwelcome stay across much of Western Europe.

France, Germany, Italy and other countries baked under a stiflingly hot and humid air mass, as weather systems that would have provided relief were rerouted far to the north and east. Cities like Paris had day after day of temperatures over 100 degrees Fahrenheit — especially problematic in a city without widespread air conditioning.

When the event ended, as many as 70,000 people had died.

A new study finds that heat waves of the severity of 2003 will be commonplace as early as the 2030s, occurring on average once every other year, thanks to manmade global warming. In fact, such events have already become far more likely than they were just about a decade ago, simply due to the shift in average temperatures that has taken place since then across Western Europe, the study found.

By the end of the century, the study says, 2003 will seem like “an extremely cold event” compared to the summers that France, Germany, Italy and other European countries will experience.

The study, published in the journal Nature Climate Change, is a followup to a groundbreaking paper published in 2004, which concluded that global warming had made the 2003 heat wave twice as likely to occur.

That 2004 study effectively launched the field of extreme event attribution That 2004 study effectively launched the field of extreme event attribution, in which climate scientists sift for clues about how a shifting global climate may influence individual extreme events. Today, the field of extreme event attribution is rapidly expanding, pushing against the limits of supercomputing and what climate scientists can say about short-term weather variability in a climate change context.

The authors of the 2004 paper repeated some of their analysis, taking into account average temperature changes that have occurred since 2003.

They found that the odds of heat waves as extreme as the 2003 event have already increased from about 1 in 1,000 in 2003 to about 1 in 100 in 2012. It projects that such heatwaves will become even more common, occurring about once every other year, as soon as the 2030s, if greenhouse gas emissions trends continue.

“Regarding the changing risk of extremes and more specifically heatwaves, we expect that as the climate warms, extreme temperature thresholds will be more frequently exceeded,” study co-author Nikolaos Christidis told Mashable. “What our study shows is that this change in the reference European region is rapid, and we estimate a large increase in the chances of heat waves has taken place in the span of the last 10 to 15 years.”

The study, as well as another new paper to be published in the journal Geophysical Research Letters, drives home the important point that shifting the global average surface temperature even slightly in a warmer direction results in a much larger increase in extreme heat events.

In the language of statistics, a shift in the normal distribution results in a much larger change in the “tails” of the distribution, which is where extreme events are found.

Between the 1990s and the decade from 2003 to 2012, summers in the region affected by the 2003 heat wave have warmed by about 1.5 degrees Fahrenheit, on average. This background warming greatly increased the chances of summer heat waves, which were defined as heat waves with temperatures higher than 2.88 degrees Fahrenheit above the 1961-1990 average, as well as the chances of extreme heat waves like the 2003 event.

The study defines such an event as having temperatures of 4.1 degrees Fahrenheit above the 1961-1990 average.

Such a spike in regional temperatures from one decade to the next is consistent for projections of climate change in Europe, says Reto Knutti, a climate scientist at ETH Zurich.

Ranked Years

“Europe is in fact one of the areas where the hot extremes changes most dramatically,” Knutti told Mashable. He said projections from the latest U.N. Intergovernmental Panel on Climate Change (IPCC) report show that precipitation may decrease in Europe, leading to greater evaporation, and in turn stronger warming. Knutti was not involved in the new study.

“The decrease in soil moisture, precipitation and atmospheric relative humidity in summer over Europe is one of the clearest signals” from climate models, Knutti added. “The increased likelihood of extremely hot days and seasons would happen to some degree without this, just as a consequence of warming, but the change in the water cycle and the resulting change in inter-annual variability probably amplifies it further.”

Other climate researchers who were not involved in the European heat study said its conclusions appear to be sound.

“The bottom line that people in Europe need to become more resilient to heat waves is totally correct,” said Gavin Schmidt, the director of NASA’s Goddard Institute for Space Studies in New York City.

Christedes, who is a senior climate scientist with the UK Met Office, says that it’s not predetermined that future heat events will cause such a high death toll compared to the 2003 disaster.

“The 2003 event exposed the vulnerability of European citizens to extremely hot summers,” he says. “The severity of the socio-economic impacts associated with such events as they are becoming more frequent will of course largely depend on how prepared societies will be to cope with these extremes.”

IMAGES:

People relax on the beach, in Barcelona, Spain, Thursday, July 17, 2014. I: MANU FERNANDEZ/ASSOCIATED PRESS

Ranked years hottest (top left) to coldest (bottom right).

IMAGE: UK MET OFFICE

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