Climate Change

		Departure of temperature from average for last month (updated by the 17th of each month) from the National Climatic Data Center.
		Average April arctic sea ice coverage as observed by satellites between 1979 and 2008. Image credit: National Snow and Ice Data Center.

April 2008 was the 13th warmest April for the the globe on record, according to statistics released by the National Climatic Data Center. The January-April year-to-date period ranked twelfth warmest. A weak La Niña event continues to cool ocean waters in the central and eastern equatorial Pacific. The La Niña event weakened considerably in April, but has stabilized just above the threshold for being classified as neutral, during the first half of May. For the contiguous U.S., April was the coolest April in 11 years for the lower 48 United States, and fell into the lowest twenty-five percent of all Aprils based on records going back to 1895, making it the 29th coolest April on record. Precipitation was near average for the month.

April 2008 Northern Hemisphere sea ice extent was the eighth lowest on record for the month of April, 7% below its extent in 1979 when satellite measurements began, according to the National Snow and Ice Data Center. April was the fifth straight month that a new monthly minimum arctic sea ice record was not set, following a string of five months in a row where monthly records were set. The past four years had the least April sea ice extent since records began in 1979, with 2007 having the least April sea ice extent on record. However, while the ice extent is not at a record low this year, the volume of the arctic sea ice is probably at a record low for April. The ice is exceptionally thin across the Arctic this winter, and the edge of this thin first-year ice extends beyond the North Pole.