"Hot summers are now much more common," said Gareth Jones of the UK's Met Office, speaking at the IUGG meeting in Perugia, Italy. "The current sharp rise in the incidence of hot summers is likely to continue."
Jones and colleagues used the HadGEM1 climate model to analyse land summer surface temperatures in the Northern Hemisphere from 1961 to 2006. The HadGEM1 model includes anthropogenic factors such as greenhouse gases, aerosols, ozone, and land use, and natural factors like volcanoes. The team looked at the frequency of warm summers with a 1 in 10 year return period.
The researchers split their analysis of the Northern Hemisphere into separate regions; in all regions apart from Central North America the model indicated an anthropogenic effect on the frequency of warm summers.
In the Mediterranean Basin, the analysis showed that warm summers that had a 1 in 10 year return period in the 1960s now have a 7 in 10 year return period.
A research paper detailing these results is due out shortly.