Posted on 12/29/2004 6:56:13 PM PST by beavus
Extreme changes in the Arctic Oscillation in the early 1990s -- and not warmer temperatures of recent years -- are largely responsible for declines in how much sea ice covers the Arctic Ocean, with near record lows having been observed during the last three years, University of Washington researchers say.
It may have happened more than a decade ago, but the sea ice appears to still "remember" those Arctic Oscillation conditions, according to Ignatius Rigor, a mathematician with the UW's Applied Physics Laboratory and a presenter at the American Geophysical Union's annual fall meeting this week in San Francisco.
The Arctic Oscillation is a seesaw pattern in which atmospheric pressure at the polar and middle latitudes fluctuates between positive and negative phases. The wind patterns associated with the Arctic Oscillation affect the surface winds and temperature over North America and Eurasia, as well as the Arctic.
The Arctic Oscillation was in an extreme "high," or positive, phase in the early '90s and is generally in a moderate phase today. Rigor and John M. Wallace, UW professor of atmospheric sciences, say the extreme high caused winds at the surface to circulate in ways that blew most of the thicker, older ice out of the Arctic Ocean into the Atlantic.
"It was as if winds generated in response to the Arctic Oscillation in those years became a far bigger 'broom' sweeping ice out of the arctic," Rigor says.
At the same time, changes in surface winds started causing the already thin ice to re-circulate back to the Alaska coast more quickly, decreasing the time it had to thicken before another melt season started. Today the ice in places remains just too thin to last through the summer melt, he says.
The result is that 70 percent of the ice is 3 years old or younger, Rigor says. In the 1980s, some 80 percent of the ice was 20 to 30 years old or more. As for ice extent -- the area of the ocean covered by ice -- last summer was again among the record low years, nearly 15 percent lower than average. With a wintertime ice pack roughly the size of the United States, that's like having areas equivalent to the states of Texas and Colorado melt away. In the 1980s, it was more an area the size of Rhode Island.
The melting in places was extensive even where local temperatures were colder than normal. This was the case in the summers of 2002 and 2003 for Alaskan coastal waters.
"The temperature itself doesn't explain it all," Rigor says, "but the age of sea ice explains more than half the variance in summer sea-ice extent in those coastal waters."
Just because warming temperatures may not be the key reason for declines in ice extent that doesn't mean greenhouse gases and warming are not contributing factors, Rigor says.
"The Arctic Oscillation has been in a primarily moderate to high phase during the last decade or more, and the only way to reproduce this tendency in the oscillation using a numerical climate model is if you include the observed increase in greenhouse gases in the model."
To estimate the age of sea ice, the researchers used a simple model that tracks a grid of ice parcels as they move about the Arctic Ocean. Data about the ice parcels comes from the International Arctic Buoy Program. Under way since 1979, the 40 buoys currently deployed in the ice are from 19 institutions in 10 countries.
The fluctuations in the Arctic Oscillation to its positive phase set the stage for the recent reductions in ice extent, and Rigor and Wallace think low summer sea-ice extents are likely to persist for at least a few years. It is conceivable that, given an extended interval of low-index Arctic Oscillation conditions, ice thickness and summertime sea-ice extent could gradually return to levels characteristic of the 1980s, they say.
A few days ago I finished Crichton's "State of Fear". A very entertaining way to catch up on your sciences while reading a great thriller.
Global warming is a farce.
I bet we'll see this on the front page of the NY Times tomorrow. /sarcasm.
You say global warming is NOT responsible for thinning Artic sea ice? Sorry, this theory does not fit the liberal weenies version of how things should be. No tenure for you at UW.
The issue is about the degree of measurable warming that can be attributed to human activity, and within that activity, what activity is most guilty.
My personal selection is the extension of irrigation to otherwise barren, dry lands. Water vapor is a tremendous greenhouse gas and increasing the amount of water vapor has to have an impact. Others believe it's your SUV. My elderly aunt Minnie believes it's all those coal furnaces used to heat the slum dwellers in New York City.
So many questions, so little time.
Let's rephrase it... global warming is not an articial phenomenon. At most what we have is LOCAL temperature changes. In some places, temperatures are rising... while in other spots temperatures are falling. Overall urban areas - where concrete and heating is abundant - are experiencing upward pressure on its temperature.
If cities and towns are warmer than the surrounding countryside it's not because they are "heat islands". Rather, it's because they have a lot more water vapor surrounding them. Irrigated farmland should also be warmer (urban or not, eh), from the same cause.
What we have is warming at the lowest elevations, in general, and cooling when you get up there several thousand feet.
I am basing my opinion on the data presented by Michael Crichton's "State of Fear". He actually bothered to include REAL scientific facts - with footnotes and everything - to make his novel more appealing.
"Global warming is a farce."
But it's the closest thing the libs have to the truth!
You haven't been to Phoenix in the summer time.
You say that the plants make it warmer but you say that it cooled down and THEN the plants died. Seems like you have it backwards.
1990's? So it's Clinton's fault!
No, it's because we have all that concrete and asphalt absorbing the heat and all the AC's pouring out heat and all the cars radiating heat and all the people massed together.
A German research team believes that it should be possible to warm up the Sahara by raising special plants that will hold in the water vapor. Given enough warmth, the monsoons should return and the place could become very productive again.
I admit that I don't entirely understand what is being said in this article. Apparently there are observed oscillations in atmospheric pressure at the poles which cause winds that begin to blow the ice away, but not in a noticable way until a few years after the winds start blowing? Do I have that right?
As an example I used the Sahara desert.
You are adding elements I didn't include, e.g. air conditioners, cars, etc.
The concrete and bare road surfaces do not retain heat as well as a well watered jungle.
You use solar mass (big rocks, concrete walls, etc.) to slow down the flow of heat into your home. You work it right, as I have, and you get heat at night and cool during the day. In the long run a whole bunch of solar mass will run cooler than a forest.
Oh. So the South American rain forests are still cooling down. I will have to remember to take my heavy coat next time.
We are talking about average annual temperature. BTW, Phoenix benefits from monsoon rains.
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