©International New York Times, by DAVID JOLLY. December 8, 2014
In June 2003, a high-pressure weather system took hold over Western Europe and hovered there for weeks, bringing warm tropical air to the region and making that summer the hottest since at least 1540, the year King Henry VIII discarded his fourth wife, Anne of Cleves.
Temperatures were about 2.3 degrees Celsius, or 4.1 degrees Fahrenheit, above average that summer, contributing to perhaps 70,000 additional deaths and hitting the elderly particularly hard. The heat was a factor in the outbreak of forest fires and in lower than usual crop yields. It caused Alpine glaciers to shrink at a rate double that seen in the previous record summer, five years earlier.
Now, three scientists from the Met Office, the British weather agency, have concluded that human-caused global warming is going to make European summer heat waves “commonplace” by the 2040s.
Their findings, published Monday in the online journal Nature Climate Change, suggest that once every five years, Europe is likely to experience “a very hot summer,” in which temperatures are about 1.6 degrees Celsius, or 2.9 degrees Fahrenheit, above the 1961-90 average. This is up from a probability, just a decade ago, that such events would occur only once every 52 years, a 10-fold increase.
To predict how global warming will play out in Europe in the years ahead, Nikolaos Christidis and two of his Met Office colleagues first looked back with a statistical tool called optimal fingerprinting. Their method, in which they entered observed data into complex mathematical models, allowed them to assign responsibility for weather events to natural or human-made factors, an approach that scientists call “climate attribution.”
Dr. Christidis and his colleagues, Gareth S. Jones and Peter A. Stott, studied historical data for an area encompassing most of Western Europe and the Mediterranean. They found a striking rise in the probability of extreme summer temperature events over just two decades, 1990-99 and 2003-12.
The study also found that the probability of a temperature increase of the magnitude experienced in the 2003 heat wave has gone from less than one every 1,000 years to about one every 127 years. That is because average temperatures have increased over the past two decades and are expected to keep rising.
“In the space of one decade, the frequency of these kinds of events changed quite a lot,” Dr. Christidis said in a telephone interview.
European summer temperatures “have increased a lot over the last 10 or 15 years,” he said. “And as the climate becomes warmer, you have more of a chance of exceeding these temperature thresholds.”
Dr. Christidis said the vulnerability of Europeans became evident during the 2003 heat wave, but he added that scientists should only report their findings, not suggest policies for adaptation. He said it was impossible to estimate what the human toll from future heat waves would be, “as this very much depends on changes that people may make to better adapt.”
Michael Oppenheimer, the Albert G. Milbank professor of geosciences and international affairs at Princeton, who was not involved in the study, said the researchers’ conclusions appeared to be plausible, as “events of extreme heat, which were previously highly unlikely to occur, have become much more likely,” even if such events are unlikely in any given year.
If carbon emissions, the main human contributor to climate change, continue to rise, he added, events that are currently rare will “become the norm by 2100.”
Dr. Oppenheimer said the specific numbers produced by the study needed “to be interpreted with caution,” because of the complexity involved in modeling the atmosphere and ensuring that the data accurately reflect what is happening in the real world.
“Nevertheless, this paper probably represents the best that can be done right now,” he said.
Note to readers:
This article has been published by the International New York Times on 8 December 2014 and written by David Jolly.
ENHANCE partners examine a tool to increase health resilience in case of heat waves. For more information access the ENHANCE web page on the case study: Health preparedness and heat wave response plans.