The Arctic sea ice maximum

NSIDC scientists announced today that the Arctic sea ice cover has likely reached its maximum extent, marking the beginning of the melt season. (For details, see Arctic Sea Ice News & Analysis). What is the sea ice maximum and why does it matter?

The maximum ice extent marks the beginning of the melt season for Arctic sea ice. Leads, long cracks in the ice, begin to open up and the ice cover starts to melt as sunlight brings warmth to the Arctic. Credit: Angelika Renner

What is the maximum and when does it happen?
Arctic sea ice melts and regrows in an annual cycle, freezing throughout the winter months and melting in the spring and summer. The ice cover generally reaches its maximum extent sometime in late February or March. After that, ice melts through the summer, hitting a low point in early or mid-September. NSIDC scientist Walt Meier said, “The maximum marks the point when the Arctic shifts from a freezing period into the summer melting period.” Continue reading

The Arctic Oscillation, winter storms, and sea ice

The Arctic Oscillation (AO) is a large-scale climate pattern that influences weather throughout the Northern Hemisphere. It alternates between a positive phase (left) and a negative phase (right). In its positive phase the AO tends to bring warmer weather to the middle latitudes, while in its negative phase, winter storms are more common in the Eastern United States and Europe. Credit: J. Wallace, University of Washington.

Last year, many scientists blamed the winter storms that blasted the Northeastern United States and Europe on the negative mode of a weather pattern called the Arctic Oscillation. This winter, the Arctic Oscillation started out in the opposite mode, which scientists connect to the warmer-than-average temperatures and unusually low snowfall over much of the U.S. The swings of the Arctic Oscillation also help control how sea ice moves in the Arctic Ocean, which is of great interest to climate scientists. Readers often write in to ask us about this powerful but mysterious climate phenomenon, and how it affects weather where they live. What is the Arctic Oscillation, and how does it affect Arctic sea ice and the rest of the Northern Hemisphere? Continue reading

An Arctic hurricane?

This satellite image from November 8 shows the hurricane-like storm that hit Western Alaska earlier this month. Credit: NASA Earth Observatory image created by Jesse Allen, using data obtained from the Land Atmosphere Near real-time Capability for EOS (LANCE).

On November 8 and 9, a strong storm hit the Western Alaska coast, bringing blizzard conditions, storm surge of up to 10 feet and wind gusts as fast as 93 miles per hour. Along the Western Alaskan coastline, towns and villages prepared for the worst. “Up here, cities are much more sparse, but a storm like this still impacts the people that live there,” said Kathleen Cole, an ice forecaster at the National Weather Service. Damage reports after the storm indicated extensive flooding, wind damage to buildings, as well as power outages, which led to many evacuations to higher ground and to shelters with generator power. Some reports referred to the storm as a “blizzicane,” or an Arctic hurricane. What was unusual about this storm—and was there any connection to changes in the Arctic climate? Continue reading

What’s in a number? Arctic sea ice and record lows

Arctic sea ice extent for September, 2011 was the second-lowest in the satellite record. However, other data sources showed that ice extent perhaps hit a new record low for several days in September. Credit: NSIDC/NASA Earth Observatory

Did Arctic sea ice reach an all-time record low this year—or not? Scientists at University of Bremen in Germany thought it was a new record, while data from NSIDC showed the sea ice at its second-lowest level. The two groups were examining data from two different satellite sensors. Why did the data differ—and if data can vary, does a record low really matter? Continue reading

Climate change or variability: What rules Arctic sea ice?

This photo, taken during the NASA ICESCAPE mission in summer 2011, shows melt ponds on the surface of Arctic sea ice. Weather patterns in the Arctic this summer have favored ice loss, leading to near-record low ice extent over most of the summer. New research is explaining how much ice loss is caused by variable conditions, and how much can be pinned on human-caused climate change. Credit: NASA/Kathryn Hansen

Arctic sea ice is near its annual low extent for the year. Will it reach a new record low? While many people are watching this year’s ice extent closely, the effect of climate change on ice extent in a single year is different than its effect in the long term. Arctic sea ice has declined more than 30 percent in summer since satellite measurements started in 1979. But from year to year, ice extent jumps up and down quite a lot. Continue reading