Recent studies show British animals migrating northwards, and spring arriving earlier right across Europe.

These are also thought to be signs of temperatures rising in Britain and western Europe, in step with the planet as a whole.

Long run

The Central England Temperature (CET) record dates back to 1659, and is the longest continuous series of temperature measurements made by instruments anywhere in the world.

Currently, measurements are made at Pershore, Rothamsted and Stonyhurst, and then averaged.

Since the 1950s, CET has risen by about 1C - more than the global average, but less than the increase recorded in parts of the world thought to be particularly sensitive to climate disruption such as the Arctic Ocean and the Antarctic Peninsula.

David Karoly (now at the University of Oklahoma) and Peter Stott of the Hadley Centre, part of the UK Met Office, used a recent computer model of climate to work out the chance that this rise was part of a natural cycle.

The probability was, they calculated, less than 5%.

Writing in the journal Atmospheric Science Letters, they conclude: "Hence, the observed annual mean warming trend over the last 50 years is very unlikely to be due to natural internal climate variability alone."

The researchers found that when they introduced into the model the factor of "anthropogenic forcing" - greenhouse gases produced by industry, transport and other human activities - the model reproduced the observed temperatures.