Update of April 16, 2008:
Arctic sea ice has continued to crack up, including the remnant of older ice located just north of Greenland and along the northernmost Canadian islands. The satellite image directly above this paragraph is from today, April 16. To compare it to the amount of older ice that was still around in February, look at the right side of the NASA graphic (click HERE) -- the second image below this paragraph -- at the areas of purple and green. Please click on any image to enlarge it.
Please click on the image to enlarge it (from the University of Illinois/University of Colorado). Link to site: http://igloo.atmos.uiuc.edu/cgi-bin/test/print.sh?fm=04&fd=11&fy=2007&sm=04&sd=11&sy=2008
The above graphic is a side-by-side comparison of the Arctic sea ice concentrations (indicated by color, burgundy being the most solid) and land snow cover on April 11, 2007, and April 11, 2008. If you were to judge solely by the amount of burgundy, you might assume that the situation this year is better than it was at this time last year. However, the graphic cannot show the thickness of the sea ice.
Below is a graphic from NASA showing the average age of Arctic sea ice during 1985 to 2000 (on the left) and the age of the sea ice this year in February. The age of the sea ice can tell us something about its thickness. The oldest ice is represented by the colors purple and green (6+ and 5 years of age, respectively). Red indicates ice that is only one year old. Notice that in February of this year there was very, very little older ice, and it was mostly located just north of Greenland and the northern islands of Canada. One-year-old ice now represents a good 70% of the coverage, and it is quite thin and will break and melt much more readily.
Please click on the graphic below to enlarge it. There is a good explanatory article on NASA's website concerning the condition of the sea ice this year. It may be found at the following link: http://www.nasa.gov/topics/earth/features/seaice_conditions_feature.html
The next image (below) is a satellite photo taken on April 4, 2008. Again, please click to enlarge it and observe the detail. Updated images may be found at this link (note that some have a lot of static and you can try again in an hour or so): http://www.weatheroffice.gc.ca/data/satellite/hrpt_dfo_ir_100.jpg
You can see that there are already cracks running through the oldest sea ice.
Now, have a look at this image from April 11, 2008. Please click on the image to enlarge it and show the detail.
These changes cannot be seen on the graphics produced by University of Illinois/University of Colorado.
Here is a repeat of the article I posted on April 7:
"Arctic Sea Ice Return Called Illusory"
Thin layer vulnerable to summer melting, federal scientists say
by Seth Borenstein, Associated Press, March 19, 2008
WASHINGTON -- 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 after a news conference. What's happening is not enough freezing, he said.
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.