March 19, 2011 — andyextance

Europe has experienced two heatwaves in the past decade unlike any experienced in the previous 500 years, and is set to see more in coming decades. The fires that scorched Russia last year were part of a heatwave hotter and even more widespread than the previous record event in 2003. “What was really striking was that there was another such enormous heatwave in Europe in such a short period,” explained Erich Fischer. Together with four other European scientists, the Swiss Federal Institute of Technology, ETH Zurich, researcher has found that major heatwaves are set to become five to ten times more likely over the next 40 years. Yet despite this, another event like 2010’s is unlikely to occur until after 2050.

In a paper published in leading academic journal Science on Thursday, the Portuguese, Spanish, Swiss and German scientists analysed the significance of last summer’s average temperatures against three different historical temperature records. Two sets together provide measured daily average temperatures across Europe back as far as 1871, while the third reconstructs average temperatures for each season back to 1500. “For 500 years further back, we use tree rings, plus ice cores, plus documentary evidence,” Fischer told Simple Climate. Tree rings show how temperatures in a given year have affected the trees’ growth rates. Likewise, ice cores show how temperatures influenced ice sheets in places like Greenland and the Arctic through time, while documentary evidence speaks for itself. “In Europe, there’s many places where people already were interested back in the 16th and 17th century in what’s going on with the weather and climate and so they would be documenting these,” Fischer noted.

Burned into history

The 2010 heatwave shattered all records, with maximum temperature measurements averaged over 7-days exceeding the average for this figure from 1871-2010 by 13.3°C. Averaged across the whole summer, 2010 in Europe was 0.2°C warmer than the previous warmest summer in 2003, with the heatwave covering around 2 million square kilometres. Looking further back, Fischer and colleagues suggest that the last decade’s summers in Europe have been significantly warmer than any other since 1500 with at least two likely to have been the warmest of the last 510 years. “The average summer temperatures have been exceptional over the last ten years, and maybe three or four further back,” Fischer said.

Fischer’s team then turned to climate models to understand whether continuing increases in greenhouse gas emissions might make these “mega-heatwaves” more frequent. To try and gauge the accuracy of their predictions, the researchers used 11 different models to predict temperatures in Europe over the decades from 2020-2049 and from 2070-2099. “Using a single model you just get one prediction and you’re almost certain you’re not going to hit the right spot,” Fischer explained. “The idea of having multiple models is to get a sense of what different outcomes you get, what uncertainties you have for the future.”

They based their predictions on Intergovernmental Panel on Climate Change (IPCC) scenario A1B, which assumes increasing equality between world regions with power generated by a balance of renewable and fossil-fuel technology. While they predict that heatwaves like 2003’s will be likely to occur in 2020-2049, a repeat of 2010 remains unlikely. However, by the end of the 21st century the models project a 2010-type heatwave every eight years on average, with heatwaves like 2003 potentially occurring every two years. But Fischer again warns that these figures are not completely certain. “The models show an increase in the frequency and intensity of the heatwave, and so we’re quite confident on that, but the exact magnitude of the change differs substantially between the models,” he said.

Researching coincidence

Fischer’s paper virtually coincides with the US National Oceanic and Atmospheric Administration (NOAA) announcing another study warning that extreme heatwaves will become more common with further climate change. That paper, which has been accepted by but is yet to be officially published in Geophysical Research Letters, claims that exclusively natural processes were mainly to blame for last year’s heat wave. Yet the NOAA team do acknowledge that the natural occurrence was extremely unlikely, as it should was expected to happen less than once every 100 years. They also draw a similar conclusion to Fischer’s team that greenhouse gas emissions will cause this probability to increase significantly by the end of this century, estimating once every 10 years.

Scientists are increasingly trying to determine whether or not individual events are caused by climate change, but the field remains young. Fischer says that he therefore cannot comment authoritatively on whether the NOAA team’s finding that 2010’s heatwave was “natural” is accurate. “This is not my area of expertise,” he conceded. “Someone is suggesting something and other people try and confirm or look at it from another perspective. That’s how science has been evolving for centuries.”

Nevertheless, Russia alone saw more than 55,000 heat-related deaths, extensive wildfires, and approximately 25 percent crop failure last year. The total economic loss was around 1 percent of Russia’s gross domestic product, according to preliminary estimates referred to by the European scientists. Both Fischer’s team’s and the NOAA’s research can help the world become better prepared for the recurrence of such disasters, he says. “Farmers can adapt or maybe change their crops,” the scientist noted. “Forest management can try to cope with increasing probability of fires. Climate science can help a lot to inform the public and decision makers how to get prepared.”