The challenging issue, he said, is that even without tipping points, sea ice can undergo periods of rapid decline. "But these rapid declines occur due to a combination of natural volatility on a declining trend," says DeWeaver, "rather than a tipping point."
"Ultimately the outcome depends on how much greenhouse gas we add to the atmosphere in the future," he said, "not how much we've added until now."
"Our research offers a very promising, hopeful message, but it's also an incentive for mitigating greenhouse emissions," said Bitz.
Because the scientists specifically looked at whether there's a tipping point beyond which seasonal Arctic ice could not recover, they used a general circulation model in which the sea ice is particularly sensitive to rising temperatures.
Previous work by Bitz and others showed that unchecked temperature increases, along with natural environmental volatility, could result in the loss of vast areas of Arctic ice in less than a decade.
It also showed that with continued business-as-usual greenhouse gas emissions, the ice did not recover and largely disappeared altogether in following decades.
However, the new Nature paper indicates that if greenhouse gas emissions were reduced substantially in the near future, rapid ice losses would be followed by substantial retention of the remaining ice through this century--and partial recovery of the ice that disappeared during the rapid ice loss.
Polar bears depend on sea ice for access to ringed and bearded seals, their primary food source. During seasons when they can't reach ice, the bears mostly go without food and can lose about two pounds a day.
The periods when they don't have ice access have increased, and are expected to continue to do so with the current level of green
|Contact: Cheryl Dybas|
National Science Foundation