Heat waves in Europe have doubled and the frequency of extremely hot days has nearly tripled in the past century. The new data show that many previous assessments of daily summer temperature change underestimated heat wave events by 30 percent. The results are published in the Journal of Geophysical Research-Atmospheres, a publication of the American Geophysical Union. “These findings provide observational support to climate modeling studies showing that European summer temperatures are particularly sensitive to global warming,” said Paul Della-Marta of the University of Bern in Switzerland. “Due to complex reactions between the summer atmosphere and the land, the variability of summer temperatures is expected to increase substantially by 2100.” JULIA WHITTY