The decade 2000-2009 was the warmest since modern recordkeeping began, and 2009 was tied for the second warmest single year, a new analysis of global surface temperature shows. The analysis, conducted each year by the NASA Goddard Institute for Space Studies (GISS), an affiliate of the Earth Institute, also shows that in half the world–the Southern Hemisphere–2009 was the warmest year yet recorded.
“There’s always an interest in the annual temperature numbers and on a given year’s ranking, but usually that misses the point,” said James Hansen, the director of GISS, which conducts a similar analysis each year. “There’s substantial year-to-year variability of global temperature. But when we average temperature over five or ten years to minimize that variability, we find that global warming is continuing unabated.”
El Niño and La Niña are prime examples of how the oceans can affect global temperatures. These terms describe abnormally warm or cool sea surface temperatures in the South Pacific, caused by changing ocean currents. Global temperatures tend to decrease in the wake of La Niña, which occurs when upwelling cold water off the coast of Peru spreads westward in the equatorial Pacific Ocean. La Niña lingered during the early months of 2009 and gave way to the beginning of anEl Niño phase in October that is expected to continue in 2010. An especially powerful El Niño cycle in 1998 is thought to have contributed to the unusually high temperatures that year, and Hansen’s group estimates that there is a good chance 2010 will be the warmest year on record if the currentEl Niño persists. At most, scientists estimate that El Niño and La Niña can cause global temperatures to deviate by about 0.2°C (0.36°F).
Warmer surface temperatures also tend to occur during particularly active parts of the solar cycle, known as solar maximums, while slightly cooler temperatures occur during lulls in activity, called minimums. A deep solar minimum has made sunspots a rarity in the last few years. Such lulls in solar activity, which can cause the total amount of energy given off by the sun to decrease by about a tenth of a percent, typically spur surface temperature to dip slightly. Overall, solar minimums and maximums are thought to produce no more than 0.1°C (0.18°F) of cooling or warming.
via Earth Institute News.
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