Sea ice in both the Arctic and Antarctic last month hit the lowest levels on record for January, the United Nations World Meteorological Organization says.
Concentrations in the atmosphere of carbon dioxide, the chief gas said to cause global warming, also hit a January record.
"It is a quite strange situation," said David Carlson, director of the World Climate Research Program, on February 17. Despite being winter, "it's extraordinarily warm in the north, and the sea ice...is at a minimum at this point in both hemispheres."
The heat content of the oceans, which is a more reliable measure of earth's warming than surface air temperatures, has been "relentlessly going up and up and up,” he said.
There have been at least three periods this winter when Arctic sea ice has retreated, when it should have been expanding, according to satellite records that go back 38 years.
This January, Arctic sea ice averaged 260,000 square kilometers less than the previous record low last January -- a shrinkage the size of the United Kingdom.
Sea ice in the Antarctic, where it is summer, was 22.8 percent below average, the organization said.
"The number of years until summer sea ice disappears [is] absolutely shortening," Carlson said.