Washington, September 4 (ANI): A new study indicates that Arctic temperatures suddenly increased during the last 50 years, after 1,900 years of natural cooling, which is additional evidence that humans are influencing climate.
Incorporating geologic records, biologic records and computer simulations, the study reconstructed Arctic summer temperatures at a resolution down to decades, and thereby extends the climate record a full 1,600 years beyond the 400 year-long record that was previously available at that resolution.
This newly lengthened record shows that recent warming was preceded by a cooling trend that lasted at least 1,900 years and should have continued throughout the 20th Century.
"These results indicate that recent warming is more anomalous than previously documented," said Darrell Kaufman of Northern Arizona University, the lead author of the study.
According to Kaufman, the results of his team's study are significant not only because of their implications for our understanding of human influences on climate change, but also because they agree with the National Center for Atmospheric Research's (NCAR) climate model, which is used for predicting future climate change.
This agreement increases confidence in the model's simulations of future climate change.
The Kaufman study is the first to quantify at a decadal resolution a pervasive cooling across the Arctic from the early part of the first millennium AD to the industrial revolution.
During this period, summer temperatures in the Arctic cooled at a rate of about 0.2 degrees Celsius per millennium, leading to the 'Little Ice Age', a period of sustained cold that ended around 1850.
"Scientists have known for a while that the current period of warming was preceded by a long-term cooling trend," said Kaufman. "But our reconstruction quantifies the cooling with greater certainty than before," he added.
The researchers believe that the long cooling trend was caused by a previously recognized wobble in the Earth's axis of rotation that slowly increased the distance between the Earth and the Sun during the Arctic summer, and thereby reduced summer sunshine in the Arctic.
But even though this cooling wobble persisted throughout the 20th Century, by the middle of the 20th Century, summer temperatures in the Arctic were about 0.7 degrees Celsius (33.3 degrees Fahrenheit) higher than would have been expected if the cooling trend had continued.
"This incongruity provides evidence of human influences on climate change," said Kaufman. (ANI)