Arctic sea ice appears to have reached a record low wintertime maximum extent for the second year in a row, according to NASA scientists.
Every year, the cap of frozen seawater floating on top of the Arctic Ocean and its neighbouring seas melts during the spring and summer and grows back in the fall and winter months, reaching its maximum yearly extent between February and April, researchers said.
On March 24, Arctic sea ice extent peaked at 14.52 million square kilometres, a new record low winter maximum extent in the satellite record that started in 1979.
It is slightly smaller than the previous record low maximum extent of 14.54 million square kilometres that occurred last year. The 13 smallest maximum extents on the satellite record have happened in the last 13 years, NASA said.
The new record low follows record high temperatures in December, January and February around the globe and in the Arctic.
"The atmospheric warmth probably contributed to this lowest maximum extent, with air temperatures up to 10 degrees Fahrenheit above average at the edges of the ice pack where sea ice is thin," said Walt Meier, a sea ice scientist at NASA's Goddard Space Flight Centre in Maryland.
The wind patterns in the Arctic during January and February were also unfavourable to ice growth because they brought warm air from the south and prevented expansion of the ice cover.
But ultimately, what will likely play a bigger role in the future trend of Arctic maximum extents is warming ocean waters, Meier said.
"It is likely that we are going to keep seeing smaller wintertime maximums in the future because in addition to a warmer atmosphere, the ocean has also warmed up. That warmer ocean will not let the ice edge expand as far south as it used to," he said.
"Although the maximum reach of the sea ice can vary a lot each year depending on winter weather conditions, we are seeing a significant downward trend, and that is ultimately related to the warming atmosphere and oceans," said Meier.
This year's record low sea ice maximum extent will not necessarily result in a subsequent record low summertime minimum extent, researchers said.
Summer weather conditions have a larger impact than the extent of the winter maximum in the outcome of each year's melt season; warm temperatures and summer storms make the ice melt fast, while if a summer is cool, the melt slows down, they said.
Arctic sea ice plays an important role in maintaining Earth's temperature - its bright white surface reflects solar energy that the ocean would otherwise absorb.
But this effect is more relevant in the summer, when the Sun is high in the sky in the Arctic, than in the winter, when the Sun does not rise for months within the Arctic Circle, NASA said.
"In the winter, the impact of missing sea ice is mostly felt in the atmosphere," said Jennifer Francis from Rutgers University.
