Jim Hansen and buds offer an explanation of the 2005 global temperature numbers, in part in response to last month’s Washington Post story on their data. Money quote:
The existing record in the period of instrumental temperature measurements occurred when the 1997-98 “El Nino of the century” occurred on the back of a strong two-decade warming trend; in addition, the global temperature impact of the El Nino, which typically lags the El Nino by a few months, coincided almost precisely with calendar year 1998. As a result, the 1998 temperature jumped about two standard deviations above the prior record. Thus, if the 1998 global temperature level is reached without help from a large El Nino, such a result would be a measure of how intense the underlying global warming trend has become.
As Roger Pielke Sr. loves to point, there’s more to climate than surface temperatures. But it is, after all, where we all live, so in terms of human understanding and experience, the number nevertheless has some relevance. And to the commenter who suggested that “a sample going back to 1880 isn’t very meaningful,” that all depends on what you mean by “meaningful.” Given that human societies make significant decisions on decadal timescales, I would argue that a climate record going back to the 1880s is meaningful. The past century’s climate sure seems meaningful to me.
(hat tip RealClimate)