James Hrynyshyn, Forecast Earth Correspondent
It seems to me that releasing a year-end analysis of temperature two weeks before the end of the year is asking for trouble. Not from a scientific point of view, because the likelihood that the remaining fornight's trends will have a significant impact on an entire year's average is practically zero, but because it's the sort of thing that make non-experts skeptical.
However, it turns out that, for analytical purposes involving dividing up the year into discrete seasons rather than a by calendar dates, it makes more sense to measure temperatures from the beginning of December through the end of November. So that explains why the UK's Met Office Hadley Centre and the Climatic Research Unit at the University of East Anglia have just released a 2008 temperature report. Their's is just one of several organizations who do this kind of thing, but there isn't a lot of conflict between each report's bottom lines. So let's see what it had to say:
... the global mean temperature for 2008 is 14.3 °C, making it the tenth warmest year on a record that dates back to 1850.... The ten warmest years on record have occurred since 1997. Global temperatures for 2000-2008 now stand almost 0.2 °C warmer than the average for the decade 1990--1999.
Does this prove anything? Not too much, but as usual, putting into a longer term context does suggest that the climate models are essentially correct. Those model predict a long-term warming of about 0.2 °C per decade (nearly 0.4 °F) and they anticipate that 2008 should exhibit a small easing off of the warming trend thanks to the La Niña effect, which redistributes ocean heat away from the surface temporarily.
Here's a useful graph that ranks years by their average temperature.
Note that the rightward trend is down because the warmest years are more recent, and so are grouped at the left. (Click on it for full size.)
As usual, there's a good overview of the science behind these kind of reports at Real Climate.