Going for the record: Can anything stop 2012 from being warmest ever?
For super-warm 2012 to end up as an average year in the lower 48 states would require an astonishing, and record-breaking, cold snap over the final four months. That's not in the forecast.
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One key reason is the apparent shift in conditions from two consecutive years of La Niña to a weak El Niño this coming winter. La Niña and El Niño represent opposite states in sea-surface temperatures and wind patterns along the equatorial Pacific. Both can affect atmospheric circulation patterns well beyond the tropics.Skip to next paragraph
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For the US, La Niña tends to push average storm tracks across the continent farther north than usual, while El Niño tends to drive them farther south. The onset of El Niño is expected to bring welcome rainfall to the Southeast and mid-Atlantic states. But the more southerly path for storms could lead to a dearth of precipitation farther north in sections of the country already hit hard by drought.
As a result, forecasters are calling for drought to continue through the end of the year for much of the western two-thirds of the US, with drought conditions likely to extend into the Pacific Northwest.
Globally, June through August posted the third warmest temperatures on record for that three-month period. January through August was the ninth warmest first eight months on record.
Of keen interest has been the dramatic decline in summer sea ice in the Arctic Ocean, which this melt season hit a record low of 1.3 million square miles – 18 percent below the previous record set in 2007 and 51 percent below levels in 1979, when consistent satellite measurements of sea ice began.
Less ice means more open ocean to absorb sunlight during the summer, energy released as heat in the fall and winter. The decline not only affects local Arctic weather patterns in the fall – found in forecasts of warmer-than-normal temperatures along northern Alaska – but researchers are beginning to uncover ways in which the heat being released deeper into an Arctic fall and winter can affect atmospheric circulation patterns at lower latitudes.
Indeed, the decline in summer ice has occurred far faster than models of global warming's effect on the top of the world predicted. For seasonal-forecasting purposes, this is prompting forecasters to rely even more heavily on their computer-based forecasts than they might otherwise, suggests Dr. van den Dool.
"The reliance on models will probably increase, because what is happening right now in the Arctic appears to be so fast that we hardly have any time to take data points and declare that we now know what is going on in the present climate," he says.
Intuition and sound judgment will remain key features of forecasts, he adds, "but it's a challenging situation."
IN PICTURES: Extreme weather 2012