Samplings: October 2007

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©iStockphoto.com/Simon Krži

The European heat wave of August 2003 killed some 35,000 people; temperatures in many places topped ninety-five degrees for as long as ten days in a row. A new study shows that the lethal hot spell was part of a century-long trend toward higher summer temperatures and longer heat waves in Europe—and that earlier studies underestimated just how unusually severe recent heat waves have been. Paul M. Della-Marta of the University of Bern in Switzerland and his colleagues analyzed weather data recorded for more than a century throughout Western Europe. The team discovered that the number of hot summer days—those among the warmest 5 percent ever recorded for their time of year—tripled from 1880 to the present. Meanwhile, the average length of heat waves doubled, to three days, and average summer temperatures rose by nearly three Fahrenheit degrees. A hundred years ago, weather stations recorded higher temperatures than a modern installation would have, because they didn’t properly shield their instruments from reflected light and heat. Della-Marta’s team made the most accurate statistical correction of that bias to date, revealing that the change in length of today’s heat waves had been underestimated by 30 percent. The trend toward longer, hotter heat waves will likely continue as the globe warms. (Journal of Geophysical Research–Atmospheres)