for National Geographic News
The dramatic loss of Arctic sea ice in recent years is the result of human-induced greenhouse gas emissions combined with natural cycles, according to a new study.
The loss of ice will likely change water temperatures and affect the circulation of ocean currents, which may alter climates around the world, the study suggests.
The study reviewed previous research of Arctic sea ice, which showed that the ice has been steadily disappearing since 1979.
In September 2005 satellite images revealed that the Arctic ice was at its lowest level in some 50 years of observation.
"If we compare how much ice we had in September 2005 with a typical September, we've lost an amount of ice about twice the size of Texas," said lead author Mark Serreze, senior researcher at the National Snow and Ice Data Center at the University of Colorado, Boulder.
"So we're talking about a lot of real estate."
There have been previous periods of Arctic warmth not attributed to human causes, Serreze said, and ice cover grows each winter only to shrink in summer.
But the current loss probably can't be ascribed to natural cycles alone, Serreze believes.
In the March 16 issue of the journal Science, Serreze and colleagues report that the evidence "strongly suggests" the ice loss is caused by human-induced global warming.
Natural Variations, Human Causes
The researchers pored over decades' worth of satellite images, as well as records from airplanes and ships, to compile a historical picture of Arctic sea ice over the past half century.
The records show that the extent of sea ice fluctuates dramatically each year, reaching its low point in September before starting to grow once more with the onset of winter.
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