Water vapour rather than carbon dioxide in the atmosphere is the main reason why Europe's climate is warming, according to a new study.

The scientists say that rising temperatures caused by greenhouse gases are increasing humidity, which in turn amplifies the temperature rise.

This is potentially a positive feedback mechanism which could increase the impact of greenhouse gases such as CO2. The research is published in the journal Geophysical Research Letters.

The scientists involved have used research networks and weather stations across Europe to measure temperature, humidity and longwave radiation, which plays a key role in the greenhouse effect.

"We observed that between 1995 and 2002, the amount of longwave radiation coming downwards to the Earth in Europe increased significantly, whereas solar radiation did not," said study leader Rolf Philipona, from the World Radiation Center in Davos, Switzerland.