Science Daily: Warming from greenhouse gases has trumped the Arctic's millennia-long natural cooling cycle, suggests new research. Although the Arctic has been receiving less energy from the summer sun for the past 8,000 years, Arctic summer temperatures began climbing in 1900 and accelerated after 1950. The decade from 1999 to 2008 was the warmest in the Arctic in two millennia, scientists report in the journal Science. Arctic temperatures are now 2.2 degrees F (1.2 degrees C) warmer than in 1900.To track Arctic temperatures 2,000 years into the past, the research team analyzed natural signals recorded in lake sediments, tree rings and ice cores. The natural archives are so detailed the team was able to reconstruct past Arctic temperatures decade by decade. As part of a 21,000-year cycle, the Arctic has been getting progressively less summertime energy from the sun for the last 8,000 years. That decline won't reverse for another 4,000 years.
The new research shows the Arctic was cooling from A.D. 1 until 1900, as expected. However, the Arctic began warming around 1900, according to both the natural archives and the instrumental records.
"The amount of energy we're getting from the sun in the 20th century continued to go down, but the temperature went up higher than anything we've seen in the last 2,000 years," said team member Nicholas P. McKay of The University of Arizona in Tucson. "The 20th century is the first century for which how much energy we're getting from the sun is no longer the most important thing governing the temperature of the Arctic," said McKay, a UA doctoral candidate in geosciences….
Researchers secure a floating platform used to take sediment cores from Sunday Lake in southwestern Alaska. Sediment generated by the small cirque glacier is carried to the lake by meltwater. The amount of sediment delivered to the lake can vary with the intensity of the summer melt season. (Credit: Darrell Kaufman, Northern Arizona University)
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