Deadly heatwaves will be more frequent in coming decades, say scientists

'Mega-heatwaves' like the one estimated to have killed tens of thousands in western Europe in 2003 will become up to 10 times more likely over the next 40 years, a study suggests
Damian Carrington guardian.co.uk 17 Mar 11;

The heatwave that scorched eastern Europe in 2010, killing thousands of people and devastating crops, was the worst since records began and led to the warmest summer on the continent for at least 500 years, a new scientific analysis has revealed.

The research also suggests that "mega-heatwaves", such as the prolonged extreme temperatures that struck western Europe in 2003 will become five to 10 times more likely over the next 40 years, occurring at least once a decade. But the 2010 heatwave was so extreme – 10C above the average for the first week of August between 1970 and 2000 – that similar events are only expected to occur once every 30 years or so.

Searing temperatures in July and August 2010 across Russia are estimated to have killed 50,000 people, say the researchers, who were led by David Barriopedro at the University of Lisbon in Portugal. Mortality rates in Moscow doubled compared with the previous year, filling morgues to capacity as people succumbed to heatstroke and respiratory problems. More heat-related deaths are expected to have occurred in the Baltic states Ukraine and Kazakhstan, though these figures have not yet been estimated.

The mega-heatwave also cut the Russian grain yield by 25%, sending food prices soaring, and left a million hectares of land burned. The nation's losses are estimated at $15bn.

The team examined the temperature, duration and spatial extent of the 2010 heatwave and found it exceeded the previous record year of 2003, which had also caused tens of thousands of deaths. The analysis, published in the journal Science, revealed the unprecedented nature of the 2010 heatwave using temperature measurements dating back to 1871 and estimates from tree rings and other proxies going back to 1500.

Record extremes were seen over an area of two million square kilometres. The heatwave was caused by high pressure weather systems lingering over the continent.

The decade up to 2010 was also exceptional, the researchers found. Across the whole of Europe, records that had held for 500 years were broken over two-thirds of the land mass.

Climate scientists expect increasing greenhouse gas concentrations in the atmosphere to raise both average temperatures and summer variability in Europe, leading to more heatwaves. The findings of the study are consistent with this, said Barriopedro: "Under global warming this kind of event will become more common. Mega-heatwaves are going to be more frequent and more intense in the future."

Previous research has shown that global warming made the 2003 heatwave at least twice as likely, but modelling studies have not yet been done that might demonstrate the link between climate change and the 2010 heatwave. Last month, scientists showed that climate change made the 2000 floods that swamped England two to three times as likely to happen.

Barriopedro said his team's new work shows there are serious risks of major harm to people and crops in the future unless action is taken. Some countries took additional precautions after the 2003 heatwave, for example providing early warning systems, cool rooms in homes for the elderly and by creating green spaces in cities that help control temperatures.

Recent Heat Waves Likely Warmest Since 1500 in Europe
LiveScience.com Yahoo News 17 Mar 11;

The intense heat wave that centered on western Russia last summer was truly a record breaker. It surpassed even 2003's scorcher in western and central Europe — which has been blamed for 70,000 deaths. And together, both of these mega heat waves have secured a place in the 500-year weather history of Europe, according to a new analysis.

The researchers also looked ahead, and found that a variety of different climate models predict an increase in mega heat waves similar to these in the 21st century for two regions within Europe.

From late July until the second week in August 2010, record heat settled across 772,204 square miles (2 million square kilometers) in Russia and Eastern Europe. In Moscow, the daytime temperatures reached 101 degrees Fahrenheit (38.2 degrees Celsius), in Kiev, nights reached 77 F (25 C), crops were destroyed, fires swept across western Russia, and preliminary estimates now put the Russian death toll at 55,000.

Researchers, led by David Barriopedro of the Instituto Dom Luiz at the University of Lisbon in Portugal, compared this mega heat wave with the one that struck western Europe seven years earlier, and found that 2010's heat wave was not only more severe, but also covered a greater area.

For a longer historical perspective, they also looked back 500 years for Europe. Since recorded weather measurements go back only to the 19th century, they looked at reconstructions of summer temperatures made by pulling together a variety of evidence, including that from tree rings, Greenland ice cores and old documentary sources.

Even taking into account the uncertainties in the reconstruction, they found that 2010 and 2003 were most likely the warmest summers since 1500. A number of other summers in the past decade were also close contenders.

Barriopedro cautions against blaming the heat waves on climate change caused by humans' greenhouse gas emissions.

"It's very difficult, if not impossible, to attribute a given extreme event, like the 2003 mega heat wave, to climate change," he told LiveScience. "What we can do is estimate what has been the contribution of humans to increase or decrease the likelihood of an analogue, an event like that."

For instance, after the devastating 2003 heat wave, British researchers led by Peter Stott, found that human activities had doubled the risk for a heat wave of the same magnitude. As for 2010's heat wave, that appears to have been caused mainly by natural, atmospheric phenomena, rather than humans' greenhouse gas emissions, wrote researchers led by Randall Dole of the National Atmospheric and Oceanic Administration (NOAA) in a study to be published in a forthcoming issue of the journal Geophysical Research Letters.

Even if we can't blame our greenhouse gas emissions for recent events, our activities do raise the likelihood of similar events in the future.

Barriopedro and his colleagues used 11 climate models to examine the outcome of a moderate scenario for greenhouse gas emissions. All models projected an increase in the frequency of mega heat waves during the 21st century in parts of Europe. In particular, they found that mega heat waves of magnitude similar to 2003 would increase by a factor of five to 10 for regions of western and eastern Europe. (The western European region included France and parts as of surrounding countries, and the eastern region included northwestern Russia and parts of the Baltic nations).

Last summer's heat wave; however, was so intense that the likelihood that these regions would suffer a heat wave of that magnitude remains fairly low until the second half of this century.

This study supports previous work that has predicted an increase in extreme weather as the Earth's surface warms, according to Barriopedro.

"Whatever the scenario you look at, you will have more frequent, more intense and longer-lasting heat waves in the upcoming decades in many places in the world," he said.

Barriopedro's collaborators are Erich Fischer of the Institute for Atmospheric and Climate Science, ETH Zurich; Jürg Luterbacher of Justus-Liebig-University in Germany; Ricardo Trigo of the University of Lisbon and Ricardo Garcia-Herrera of the Agencia Estatal de Meteorologicia in Spain.

The research will be published in the March 18 issue of the journal Science.