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

Sea ice down under: Antarctic ice and climate

The sea ice cover surrounding the continent of Antarctica is on average thinner than Arctic sea ice, and more susceptible to winds. This photo, from a 2003 research cruise, shows the trail of open water left by a research ship. In the background, an iceberg towers above the thinner sea ice cover. Credit: Ted Scambos, NSIDC

The Arctic Ocean is not the only place with sea ice. The ocean surrounding the continent of Antarctica also freezes over each winter. But we don’t hear much about sea ice on the bottom of the planet. What’s happening to Antarctic sea ice and why does it matter?

One reason that we hear less about Antarctic sea ice than Arctic sea ice is that it varies more from year to year and season to season than its northern counterpart. And while Arctic ice has declined precipitously over the past thirty years of the satellite record, average Antarctic sea ice extent has stayed the same or even grown slightly. 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

Summer predictions for Arctic sea ice

graph of estimates from the SEARCH sea ice outlook

Last week, an international group of researchers released their best estimates for Arctic sea ice extent over the summer melt season. The scientists are compiling their estimates so that they can better predict changes in Arctic sea ice. Credit: SEARCH Sea Ice Outlook

Average Arctic sea ice extent this May was the third lowest in the satellite record. Does that mean that ice extent will reach a new record low this summer? Or will it recover somewhat over recent years?

Last week sea ice scientists from around the world shared their best answers to those questions, in the June report of the Sea Ice Outlook. For the report, the researchers used a variety of methods to predict how sea ice will behave this summer, such as statistical methods or computer models. Continue reading