Arctic Ice Returns, Thin and Tentative

Andrea Thompson, LiveScience.com Yahoo News 18 Mar 08;

Arctic ice has reformed rapidly this winter after a record summer low, but it still covers less of the Arctic Ocean than it did in previous decades, NASA scientists announced today in an update of the states of Arctic and Antarctic sea ice.

March is the month where Arctic sea ice traditionally hits its highest extent after the Northern Hemisphere winter and Antarctic sea ice reaches its lowest extent. NASA satellites have monitored sea ice coverage over both poles for nearly 40 years.

Arctic sea ice reached a record low this past summer, with 23 percent less sea ice cover than the previous record low and 39 percent less than the average amount that has previously spanned the Arctic Ocean in the summer months.

This extraordinarily high melt opened the fabled Northwest Passage and spurred scientists' worries about whether the Arctic ice had reached a tipping point, where melting begins to spiral out of control.

NASA's satellite observations showed that while this winter's ice extent didn't dip below previous records, it was still well below the average amount seen in the past.

Antarctic sea ice has largely remained stable over the years of NASA's observations. The Antarctic has little long-term sea ice and a different climate and weather regime than the Arctic.

Ice ages

The area of ocean covered by sea ice isn't the only factor in the "health" of the Arctic ice.

Arctic sea ice comes in two types: older, thicker perennial ice that has survived at least one summer melt season and younger, thinner seasonal ice that forms in the winter and melts again in the summer.

Seasonal ice melts more easily because it is thin and salty, and so "it's flexible and crushable and more susceptible to winds and currents," said Seelye Martin of NASA's Cryospheric Sciences Program.

Colder temperatures in parts of the Arctic increased the amount of thin, seasonal ice that formed this winter. So while Arctic sea ice was dominated by multiyear, perennial ice in past decades , it is mostly now younger, newly-formed ice.

The amount of older, perennial sea ice has substantially decreased over the past few years, and "has reached an all-time minimum," Martin said. This low is in part due to the substantial 2007 summer melt, attributed in part to climate change.

Future of the Arctic

What these colder temperatures and the slightly higher winter extent this year will mean come summer is uncertain. But because the majority of the ice is young and thin, it would be more susceptible to summer melt.

Whether any perennial sea ice will recover is also uncertain, but "it's not likely that the perennial ice cover will recover [to where it was in the past] in the near future," said Josefino Comiso of NASA's Goddard Space Flight Center in Greenbelt, Md.

Some of the seasonal ice could become perennial sea ice if summer conditions are cooler than normal this year, Meier noted, as some of the seasonal ice has formed higher north than ever before.

But, "one cold summer is not going to do it, one cold winter is not going to do it," Meier said. Numerous years of colder temperatures would be needed to restore the Arctic sea ice to where it was in the 1980s, and that is not likely to happen with the increasing levels of heat-trapping greenhouse gases in the atmosphere, he added.

Arctic sea ice builds, but vulnerable
Seth Borenstein, Associated Press Yahoo News 18 Mar 08;

Critical Arctic sea ice this winter made a tenuous partial recovery from last summer's record melt, federal scientists said Tuesday. But that's an illusion, like a Hollywood movie set, scientist Walter Meier of the National Snow and Ice Data Center said. The ice is very thin and vulnerable to heavy melting again this summer.

Overall, Arctic sea ice has shrunk precipitously in the past decade and scientists blame global warming caused by humans.

Last summer, Arctic ice shrank to an area that was 27 percent smaller than the previous record. This winter, it recovered to a maximum of 5.8 million square miles, up 4 percent and the most since 2003, NASA ice scientist Josefino Comiso said. It is still a bit below the long-term average level for this time of year.

"What's going on underneath the surface is really the key thing," Meier said in an interview following a news conference. What's happening is not enough freezing.

Summer Arctic sea ice is important because it's intricately connected to weather conditions elsewhere on the globe. It affects wind patterns, temperatures farther south and even the Gulf Stream, acting as a sort of refrigerator for the globe, according to scientists.

"What happens there, matters here," said Waleed Abdalati, chief ice scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "Climate for the period of human record has depended on the ice being there."

Viewing the Arctic from space via NASA satellites might make you think the Arctic ice cover is on its way back.

But more than 70 percent of that sea ice is new, thin and salty, having formed only since September, Comiso said. The more important ice is perennial sea ice that lasts through the summer, and that ice has hit record low levels.

Compared to the 1980s, the Arctic has lost more than half of its perennial sea ice and three-quarters of its "tough as nails" sea ice that is six years or older, Meier said. The amount of lost old sea ice is twice the area of the state of Texas, he said.

On top of that, a change in Arctic atmospheric pressure this winter is pushing a large amount of the valuable older ice out of the Arctic to melt, Meier said.

That means next summer when temperatures warm, expect lots of melting, the scientists said.

"We're in for a world of hurt this summer," ice center senior scientist Mark Serreze told The Associated Press. Depending on the weather, there could be as much melting this year as last, maybe more, Serreze and Meier said.

At the South Pole, in Antarctica, sea ice seems stable, even slightly above normal, the scientists reported. However, ice levels in Antarctica always are quite different from the Arctic and aren't as connected to the world's weather.

Thickest, oldest Arctic ice is melting
Deborah Zabarenko, Yahoo News 18 Mar 08;

The thickest, oldest and toughest sea ice around the North Pole is melting, a bad sign for the future of the Arctic ice cap, NASA satellite data showed on Tuesday.

"Thickness is an indicator of long-term health of sea ice, and that's not looking good at the moment," Walt Meier of the National Snow and Ice Data Center told reporters in a telephone briefing.

This adds to the litany of disturbing news about Arctic sea ice, which has been retreating over the last three decades, especially last year, when it ebbed to its lowest level.

Scientists have said the trend is spurred by human-generated climate change.

Melting Arctic ice does not raise sea levels as the melting of glaciers on Greenland or Antarctica could, but it does contribute to global warming when reflective white ice is replaced by dark water that absorbs the sun's heat.

Using satellites that measure how much ice covers water in the Arctic and Antarctic, Meier and other climate scientists found a steep drop in the amount of perennial ice -- the hardy, thick ice that is over a year old -- in the north.

The oldest Arctic ice that has survived six years or more is the toughest, and even that shrank dramatically, Meier and the other scientists said.

OLD ICE "TOUGH AS NAILS"

Some 965,300 square miles of perennial ice have been lost -- about one and a half times the area of Alaska -- a 50 percent decrease between February 2007 and February 2008, Meier said.

The oldest "tough as nails" perennial ice has decreased by about 75 percent this year, losing 579,200 square miles (1.5 million sq kms, or about twice the area of Texas, he said.

This doesn't mean the Arctic is open water during the winter, but it does mean that in many areas, the stronger perennial ice is being replaced by younger, frailer new ice that is more easily disturbed by wind and warm sea temperatures.

"It's like looking at a Hollywood set," Meier said of an Arctic largely covered with younger ice. "It may look OK but if you could see behind you'd see ... it's just empty. And what we're seeing with the ice cover is it's becoming more and more empty underneath the ice cover."

Perennial ice is also vulnerable to a recurring pattern of swirling winds and currents known as the Arctic oscillation, which ejects the old ice out of the zone around the pole and aims it south where warmer waters will melt it.

The scientists also analyzed satellite data for Antarctica but found less dramatic change there.

This was attributed to the difference in the two polar regions. The Arctic is an ocean surrounded by land while the Antarctic is a continent surrounded by ocean.

However, the scientists noted sharp warming on the Antarctic Peninsula, which stretches northward from the southern continent toward South America.