Last year's hot weather in France made August miserable for most citizens and claimed thousands of lives. Climate modeling results published today in the journal Science indicate that heat waves at the end of the 21st century will be more severe, more frequent and longer lasting than those of recent years.

Gerald Meehl and Claudia Tebaldi of the National Center for Atmospheric Research (NCAR) utilized the Parallel Climate Model to investigate the behavior of future heat waves. Extreme weather events will have some of the most severe impacts on human society as climate changes, Meehl remarks. The researchers ran the model for both the 20th century, using data from 1961 to 1990, and the 21st, predicting events for 2080 to 2099, assuming little in the way of policy intervention for greenhouse gas emissions.

Using Paris and Chicago as focal points for Europe and North America, respectively, the team determined that the atmospheric circulation pattern seen during heat waves is likely to become more pronounced as greenhouse gas concentrations rise. For example, heat events in Chicago currently last between 5.39 and 8.85 days, but the new findings indicate that they will stretch to between 8.5 and 9.24 days in the future. Paris, meanwhile, might experience heat waves lasting up to 17 days instead of between eight and 12. This study provides significant insight into the complex response of global climate to possible future worldwide economic and regulatory policies, comments Cliff Jacobs, atmospheric science program director for the National Science Foundation (NSF). The societal implications of this study need to be further explored.