La Nina events typically coincide with cooler global temperatures and 2008 is slightly cooler than the norm under current climate conditions. Professor Phil Jones at the CRU said: 'The most important component of year-to-year variability in global average temperatures is the phase and amplitude of equatorial sea surface temperatures in the Pacific that lead to La Nina and El Nino events'.
The ten warmest years on record have occurred since 1997. Global temperatures for 2000-2008 now stand almost 0.2 degrees C warmer than the average for the decade 1990-1999.
Dr Peter Stott of the Met Office says our actions are making the difference: 'Human influence, particularly emission of greenhouse gases, has greatly increased the chance of having such warm years. Comparing observations with the expected response to man-made and natural drivers of climate change it is shown that global temperature is now over 0.7 degrees C warmer than if humans were not altering the climate.'
Calculating the changing risk attributable to human influence is part of an ongoing collaboration between the Met Office Hadley Centre and the University of Oxford. Commenting on the dramatically increased odds of such warm years because of human induced climate change, Dr Myles Allen from Oxford University said: 'Globally this year would have been considered warm, even as recently as the 1970s or 1980s, but a scorcher for our Victorian ancestors.'
Beneath the underlying warming, temperature continues to fluctuate from year to year as a result of natural variations. Stott added: 'As a result of climate change, what would once have been an exceptionally unusual year has now become quite normal. Without human influence on climate change we would be more than 50 times less likely of seeing a year as warm as 2008.'