Doyle Rice

USA TODAY

There is now less sea ice on Earth than at any time on record. Ice in the Arctic and Antarctic melted to record low levels in January, scientists reported this week.

Sea ice is frozen ocean water that melts during the summer and refreezes in winter. It floats on top of the ocean.

Arctic sea ice this January averaged 5.17 million square miles, the lowest for the month in the 38-year sea ice record, the National Snow and Ice Data Center said.

That is 100,000 square miles less than the previous January record low set just last year.

January air temperatures climbed above average over nearly all of the Arctic Ocean, NASA said, continuing a pattern that started in fall. In some parts of the Arctic, temperatures reached a whopping 9 degrees above average for the month.

At the bottom of the world, sea ice is also at all-time record low levels around Antarctica, the data center said. The lack of ice in the Antarctic, where it is currently summer, is most pronounced in the Amundsen Sea, where only a few scattered patches of ice remain.

Sea ice in the Arctic affects wildlife such as polar bears, seals and walruses. It also helps regulate the planet’s temperature by influencing the circulation of the atmosphere and ocean. It can affect weather in the U.S.

The amount of summer sea ice in the Arctic has steadily declined over the past few decades because of man-made global warming, according to the National Oceanic and Atmospheric Administration.

"Greenhouse gases emitted through human activities and the resulting increase in global mean temperatures are the most likely underlying cause of the sea ice decline," the snow and ice data center said.

Sea ice thickness also substantially declined in the latter half of the 20th century, the snow and ice data center said.

Antarctic ice fluctuates wildly year to year, and the link to man-made global warming there is not clear, NASA ice expert Walt Meier said.

Using paleoclimatic data, studies suggest sea ice is shrinking to levels not seen in thousands of years.