Science Source

Human contribution to the European heatwave of 2003

States that the summer of 2003 was probably the hottest in Europe since at latest AD 1500, and unusually large numbers of heat-related deaths were reported in France, Germany and Italy
States that it is an ill-posed question whether the 2003 heatwave was caused, in a simple deterministic sense, by a modification of the external influences on climate—for example, increasing concentrations of greenhouse gases in the atmosphere—because almost any such weather event might have occurred by chance in an unmodified climate
States, however, it is possible to estimate by how much human activities may have increased the risk of the occurrence of such a heatwave
Uses this conceptual framework to estimate the contribution of human-induced increases in atmospheric concentrations of greenhouse gases and other pollutants to the risk of the occurrence of unusually high mean summer temperatures throughout a large region of continental Europe
Estimates it is very likely (confidence level >90%) that human influence has at least doubled the risk of a heatwave exceeding this threshold magnitude, using a threshold for mean summer temperature that was exceeded in 2003, but in no other year since the start of the instrumental record in 1851
Finds the best estimate is that climate change in made such an extreme heat event 4 times as likely