Arctic’s Winter Sea Ice Drops to Its Lowest Recorded Level
After a season that saw temperatures soar at the North Pole, the Arctic has less sea ice at winter’s end than ever before in nearly four decades of satellite measurements.
The extent of ice cover — a record low for the third straight year — is another indicator of the effects of global warming on the Arctic, a region that is among the hardest hit by climate change, scientists said.
“This is just another exclamation point on the overall loss of Arctic sea ice coverage that we’ve been seeing,” said Mark Serreze, the director of the National Snow and Ice Data Center, a government-backed research agency in Boulder, Colo. “We’re heading for summers with no sea ice coverage at all.”
“这只是我们看到的北极海冰覆盖范围总体缩减再次发出的警告，”美国科罗拉多州博尔德由政府支持的研究机构国家冰雪数据中心(National Snow and Ice Data Center)主任马克·塞雷泽(Mark Serreze)说。“我们即将迎来完全没有海冰覆盖的夏季。”
Dr. Serreze said that such a situation, which would leave nothing but open ocean in summer until fall freeze-up begins, could occur by 2030, although many scientists say it may not happen for a decade or two after that.
The melting of sea ice does not raise sea levels, but loss of ice coverage can disrupt ecosystems. For example, it can affect the timing of blooms of phytoplankton, the microscopic organisms at the bottom of the ocean food chain.
Less ice coverage also means that there is more dark ocean to absorb more of the sun’s energy, which leads to more warming and melting in a feedback loop called Arctic amplification.
The data center said on Wednesday that sea ice in the Arctic had reached maximum extent, of about 5.5 million square miles, on March 7. That is an area nearly twice the size of Australia, but about 470,000 square miles less than the average maximum from 1981 to 2010.
Much of the ice also appears to be thinner than normal, Dr. Serreze said, another result of the unusually warm temperatures in the Arctic this winter.
Late last fall, parts of the Arctic were more than 35 degrees Fahrenheit warmer than observed averages, and at the pole itself, mean temperatures for November were 23 degrees above normal. There were similar temperature spikes in December and this year.
“The Arctic Ocean was extremely warm over the winter, and there was a very impressive series of heat waves,” Dr. Serreze said. “I’ve never seen anything like this before.”
Less coverage and thinner ice mean that this summer’s minimum, which is expected to occur in September, is likely to be low. But there is no direct link between the maximum in March and the minimum after the melting season, said Walt Meier, a research scientist at the NASA Goddard Space Flight Center Cryospheric Sciences Laboratory.
面积越来越小的海冰和越来越薄的冰层，意味着将于今年夏天9月出现的最小覆盖面积很可能会极低。但瓦尔特·迈耶(Walt Meier)表示，目前3月的最大覆盖面积和冰雪融化季节过后的最小覆盖面积之间没有直接关系。迈耶是NASA戈达德太空飞行中心冰冻圈科学实验室(NASA Goddard Space Flight Center Cryospheric Sciences Laboratory)研究员。
“Just because it’s a record low maximum, there’s no prediction it will be a record low minimum in September,” Dr. Meier said. “But while a lot can happen in the summer, when you start out at such a low level, you’re not going to get a very high minimum.”
Dr. Meier said that in addition to the low overall ice extent, some parts of the Arctic were almost completely devoid of ice this winter, including the Barents Sea off Norway and Russia.
“We haven’t seen much there at all,” he said, “and what there is will melt very quickly.”