Researchers have managed to replicate the effect of cosmic rays on the aerosols in the atmosphere that help to create clouds. Henrik Svensmark, a weather scientist in Denmark, said the experiments suggested that man's influence on global warming might be rather less than was supposed by the bulk of scientific opinion.

Cosmic rays — radiation, or particles of energy, from stars, which bombard the Earth — can create electrically charged ions in the atmosphere that act as a magnet for water vapour, causing clouds to form.

Dr Svensmark suggests that the Sun, at a historically high level of activity, is deflecting many of the cosmic rays away from Earth and thus reducing the cloud cover.