The heat is on, at least in the Arctic.
Average summer temperatures in the Eastern Canadian Arctic during the last 100 years are higher now than during any century in the past 44,000 years and perhaps as long ago as 120,000 years, says a new 麻豆视频 study.
The study is the first direct evidence that the present warmth in the Eastern Canadian Arctic exceeds the peak warmth there in the Early Holocene, when the amount of the sun鈥檚 energy reaching the Northern Hemisphere in summer was roughly 9 percent greater than today, said CU-Boulder geological sciences Professor Gifford Miller, study leader. The Holocene is a geological epoch that began after Earth鈥檚 last glacial period ended roughly 11,700 years ago and which continues today.
Miller and his colleagues used dead moss clumps emerging from receding ice caps on Baffin Island as tiny clocks.听 At four different ice caps, radiocarbon dates show the mosses had not been exposed to the elements since at least 44,000 to 51,000 years ago.
Since radiocarbon dating is only accurate to about 50,000 years and because Earth鈥檚 geological record shows it was in a glaciation stage prior to that time, the indications are that Canadian Arctic temperatures today have not been matched or exceeded for roughly 120,000 years, Miller said.
鈥淭he key piece here is just how unprecedented the warming of Arctic Canada is,鈥� said Miller, also a fellow at CU-Boulder鈥檚 Institute of Arctic and Alpine Research. 鈥淭his study really says the warming we are seeing is outside any kind of known natural variability, and it has to be due to increased greenhouse gases in the atmosphere.鈥�
Miller and his colleagues compiled the age distribution of 145 radiocarbon-dated plants in the highlands of Baffin Island that were exposed by ice recession during the year they were collected by the researchers. All samples collected were within 1 meter of the ice caps, which are generally receding by 2 to 3 meters a year. 鈥淭he oldest radiocarbon dates were a total shock to me,鈥� said Miller.
Located just east of Greenland, the 196,000-square-mile Baffin Island is the fifth largest island in the world.听 Most of it lies above the Arctic Circle. Many of the ice caps on the highlands of Baffin Island rest on relatively flat terrain, usually frozen to their beds. 鈥淲here the ice is cold and thin, it doesn鈥檛 flow, so the ancient landscape on which they formed is preserved pretty much intact,鈥� said Miller.
To reconstruct the past climate of Baffin Island beyond the limit of radiocarbon dating, Miller and his team used data from ice cores previously retrieved by international teams from the nearby Greenland Ice Sheet.听
The ice cores showed that the youngest time interval from which summer temperatures in the Arctic were plausibly as warm as today is about 120,000 years ago, near the end of the last interglacial period. 鈥淲e suggest this is the most likely age of these samples,鈥� said Miller.
The new study also showed summer temperatures cooled in the Canadian Arctic by about 5 degrees Fahrenheit from roughly 5,000 years ago to about 100 years ago 鈥� a period that included the Little Ice Age from 1275 to about 1900.
鈥淎lthough the Arctic has been warming since about 1900, the most significant warming in the Baffin Island region didn鈥檛 really start until the 1970s,鈥� said Miller. 鈥淎nd it is really in the past 20 years that the warming signal from that region has been just stunning. All of Baffin Island is melting, and we expect all of the ice caps to eventually disappear, even if there is no additional warming.鈥�
A paper on the subject appeared online Oct. 23 in Geophysical Research Letters, a journal published by the American Geophysical Union.
Photo of Professor Gifford Miller on Baffin Island courtesy of Matthew Kennedy, Earth Vision Trust.
