Though scientists tend to agree that summer ice at the North Pole will eventually disappear, they haven’t yet settled on a date.
US researchers claim to have found evidence that accelerated melting has crossed a “tipping point” from which there is no going back.
The amount of summer ice at the North Pole has steadily declined since 1979, according to satellite images. Computer models predict that this trend will continue, leaving the Arctic completely ice-free during the summers as early as 2030.
In 2007, though, the ice surprised everyone by contracting far more rapidly than the models predicted. A particularly warm summer left only 4.28 million square kilometres by September – a record 23% below the previous minimum.
Accelerated Ice Loss
At the time, researchers including Mark Serreze of National Snow and Ice Data Center in Boulder, Colorado claimed that the Arctic had reached a “tipping point” — a dramatic and irreversible slide towards ice–free conditions.
At the end of September 4.67 million square kilometres remained.
Over the past five years we have seen acceleration of ice loss. Though 2008 did not beat the record set by 2007, it is still the second-lowest amount on record, below the record lows of 2002 and 2005.
Serreze and his colleagues, speaking at the American Geophysical Union (AGU) meeting in San Francisco this week, presented new evidence for a mechanism driving this acceleration.
Dramatic Changes
During the summer, as ice melts, it is replaced by dark ocean waters that absorb heat. When the cooler winter weather arrives, the oceans release this warmth, creating a pocket of higher temperatures above the Arctic that slows down the regrowth of sea ice during the winter.
By measuring the air temperature directly over the Arctic after the end of the summer melt, Serreze found a large amount of released heat. Temperatures in areas losing ice were as much as 5° C higher over the last four years as compared to the historic average.
The computer models predict this “Arctic acceleration,” says Serreze but 20 years into the future. “The models are giving us the big picture of what is going on, but it’s all happening much faster than expected,” he says.
This change may already be irreversible, as the extra heat creates a runaway thinning of ice that will soon be unable to survive in the summer Sun. If it disappears entirely during the summers, the ramifications would be global.
“The Arctic is the heat sink of the Northern hemisphere; the circulation patterns of the oceans could change dramatically,” says Serreze
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