Wednesday, December 09, 2009

Warmest Decade on Record

Cartoon by Pat Bagley of the Salt Lake Tribune

Occasionally I see arguments that climate change has slowed down or reversed course. Such arguments usually cite 1998 as the warmest year on record and insist that the (slightly) cooler years since then mean that we have nothing to worry about. However, if you look at a longer trend, the present decade looks less like a reprieve than a plateau on a continuing trend. The years 2000-2009 are the warmest decade on record, and 2009 is on track to be the fifth-warmest year.
While 1998 is still considered the warmest year on record, researchers say that preliminary data shows 2009 will likely be the fifth warmest. The analysis also shows that while the US and Canada experienced cooler than average temperature this year, temperatures in Southeast Asia and Africa could be the warmest yet.

Warmer temperature exacerbated drought conditions across the world. According to WMO, China experienced its worst drought in five decades. Drought in East Africa killed tens of thousands of livestock, while a poor monsoon season hit India's agriculture hard. A crippling drought in Australia also continued unabated this year.

Temperature data is collected from climate and weather stations around the world, ships and buoys on the sea, and satellites.
The record achieved is, of course, the modern record as established by instrumental data since the middle of the nineteenth century. Unfortunately we do not have instrumental records going beyond that. However, analysis of physical records such as tree rings and ice cores, both of which are sensitive to changes in temperature, suggests that current temperatures are higher than they have been in the past millennium. Atmospheric carbon levels are also at all-time highs, according to physical evidence.

A second point worth noting in this recent report is that lower temperature or cooler weather in one region or even continent is not a sign that the global warming trend has stopped. The study of climate change is based on long-term averages of much larger areas.

IPCC graph of the average global temperature for the past 140 years and Northern Hemisphere temperature for the past 1000 years