Temperatures hit record highs globally. El Nino or global warming?

You might have missed it if you live in many spots in the lower 48 states, but the first six months of 2010 were the warmest on record globally, according to preliminary data from the National Climatic Data Center in Asheville, N.C.

During the January-to-June period, combined land and ocean surface temperatures around the globe ran 1.22 degrees Fahrenheit above the 20th-century average.

Temperatures also ran above normal along the US East Coast. But in the the upper Midwest, the Pacific Northwest, the Rocky Mountain states, and the Southeast, temperatures ran from 2 to 3 degrees F below the long-term average.

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"We haven't seen the warming in the 48 states, which is kind of nice," says David Pierce, a climate scientist at the Scripps Institution of Oceanography in La Jolla, Calif. "But the rest of the world has really seen warm conditions."

One of the drivers behind the warm first half was El Nino – a condition in which a deep pool of warm water in the tropical Pacific migrates from its hot spot in the western part of the ocean to the waters off of wester South America. The thunderheads that tower above that pool and help drive atmospheric circulation patterns move east as well, altering the circulation patterns as they travel.

That led to warmer-than-normal temperatures in the usual locations in the tropics – in Africa and southern Asia, for instance.

But El Nino's reach also extended more indirectly to much of Alaska, Canada, and southern Greenland. Indeed, these areas experienced the most significant warming of any on the planet during the first half of the year, according to the NCDC's data.

As Washington takes a self-imposed political break from battles over energy and climate legislation, some researchers see a cautionary tale in these first-half temperatures.

To be sure, the fingerprint of global warming appears in long-term trends, not in single storms or a single season's worth of data, they agree. But human-triggered warming – through rising carbon-dioxide emissions from cars, factories, and power plants and through land-use changes – is a likely contributor to the six-month figures.

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