Tuesday, May 4, 2010

Sea Ice in Constant Retreat

Here we actually get some hard facts and a measure for the present annual ice loss.  We have had a net loss of 7500 cubic kilometers over the past decade.  Prior to that the ice had been reduced by sixty percent over what is possibly as short a time frame as twenty years.  If we accept instead that is occurred over forty years then we presently should be at the twenty five percent mark.  If we take the more aggressive position then we could be down to ten percent of the original cover.

The bad news is that observation is supporting been closer to the lower end of the range.

The second item continues to mistake surface area for volume.  If the arctic were a flat mill pond and winter fell it would have one hundred percent coverage in a night.  A little thin perhaps but you get the message.

The losses have been mostly sustained in the long term ice which has practically disappeared.

I think we are on the verge of large open spans during the summer melt all through the arctic, with winds accelerating the process.

I have seen no real encouragement for thinking that the ice got thicker than expected this winter.

Global Floating Ice in "Constant Retreat": Study

April 28, 2010

LONDON (Reuters) - The world's floating ice is in "constant retreat," showing an instability which will increase global sea levels, according to a report published in Geophysical Research Letters on Wednesday.

Floating ice had disappeared at a steady rate over the past 10 years, according to the first measurement of its kind.

"It's a large number," said Professor Andrew Shepherd of the University of Leeds, lead author of the paper, estimating the net loss of floating sea ice and ice shelves in the last decade at 7,420 cubic kilometers.

That is greater than the loss of ice over land from the Greenland and Antarctic ice sheets over the same time period, highlighting the impact of warming oceans on floating ice.

Ice melt ebbs and flows from winter to summer. The report's calculations referred to the net loss over the past decade.

"There's a constant rate of retreat (annually)," said Shepherd. "It's a rapid process and there's no reason why it won't increase over the next century."


The study did not shed new light on how soon the North Pole may be ice-free in summer, which many climate experts say could happen by 2050, perhaps even earlier.

Melting of floating sea ice and ice shelves adds little to sea level rise, because their entire mass is already in the water. By contrast, ice on land which melts into the sea will add to levels according to the equivalent of its entire weight.

If all the world's floating ice melted it would add about 4 centimeters to sea levels. But this could have a bigger effect by unblocking glaciers over land, which could then slide faster into the sea, and also because open water reflects less sunlight than ice, warming the local area.

If all the world's polar ice melted it would raise sea levels by about 70 meters, scientists estimate. "We're moving into an era where the sea ice and ice shelves are being eroded away because of temperature rise," said Shepherd.

Floating ice adds very little to sea levels, because it does not add to the total weight of water already in the sea, but it does add a little because ice contains no salt and so dilutes the ocean as it melts, causing the sea to expand in volume.

Melt of floating ice in the past decade had increased the volume of the world's seas by 193 cubic kilometers in this way, said Shepherd. Directly, that would add to sea level rise by the width of a few human hairs, he added.

Copyright 2010 Reuters News Service. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

Winds From Siberia Reduce Arctic Sea Ice Cover

Tuesday, April 27, 2010

The answer is blowing in the wind:Winds from Siberia reduce Arctic sea ice cover

The ice cover in the Arctic has decreased dramatically in recent years. Norwegian researchers have discovered that changes in air circulation patterns create winds that push away the ice.

In recent years, satellite images have shown large variations in the ice cover around the North Pole. The images have also shown that the ice cover in the Arctic has diminished considerably over the past 30 years, with the most drastic reductions occurring in recent years. (For a different viewpoint read: Scientist Says Arctic Warming Likely To Reverse; Ice Cover Growing)

Climate change or other causes?

The media regularly cite sources who believe that it is now only a matter of decades before climate change results in a totally ice-free Arctic during parts of the year. For instance, the UN Intergovernmental Panel on Climate Change (IPCC) projects that this may occur by the end of this century.

How much of the change in ice cover is caused by dramatic changes in the climate, and how much is the result of other factors? And what is causing the ice cover in the Arctic to disappear even faster than the climate models project?

The Arctic climate paradox

A few years ago, US researchers discovered what they termed the “Arctic climate paradox”. Since 1980, the researchers had been observing a decrease in ice cover. They explained this through a slow process of climate change combined with fluctuations in patterns of atmospheric pressure and air currents over the Arctic. It was believed that the positive phase of the Arctic Oscillation (AO) was a major cause of the receding ice cover.

The AO is normally influenced by three pressure systems located over the Azores, Iceland and the Northern Pacific Ocean. Since 2000 the AO has been in a negative phase. As a result, researchers predicted that the pace of reduction in the ice cover would slow down.

Instead it accelerated.

Unknown factor

“The US researchers argued that the ice was responding to something else, another factor that nobody had considered,” explains Asgeir Sorteberg, Associate Professor at the Geophysical Institute at the University of Bergen. He has been investigating this phenomenon along with his colleagues in the project entitled the Norwegian Component of the Ecosystem Studies of Sub-Arctic Seas (NESSAS).

When the Norwegian researchers began their work, they noticed in particular a dramatic change in the weather pattern in the Arctic beginning about the year 2000. The change corresponded to the point in time when the reduction of ice cover in the Arctic began to accelerate.

The answer is blowing in the wind

The researchers began to analyse the circulation patterns over the Arctic.

“We found that these patterns can explain in large part why the ice cover decreased so much more rapidly after 2000. Wind patterns depend on the position of major high-pressure and low-pressure systems. We discovered that months with very little ice cover and high temperatures corresponded with crucial variations in the wind patterns,” explains Mr Sorteberg.

“Up until 2000, the Arctic Oscillation (AO) had the greatest impact on the winter ice cover in the Arctic. But the change around 2000 meant that more of the weather and wind over the Arctic after that year was determined by high-pressure and low-pressure systems in northern Russia. In other words, the AO, which was usually so crucial, played a much less important role.”

Ice is pushed away

“We have now managed to document what has occurred in connection with this change,” says Mr Sorteberg.

The changed wind direction pushes large ice masses away from the Arctic and down along the eastern coast of Greenland. At the same time, less ice forms when the winds over the Arctic are determined by the pressure systems in northern Russia rather than those over the North Atlantic and the Pacific Ocean, as is normally the case.

Extent of ice a poor indicator

The conclusion from this research is that we should be cautious about using the extent of the ice cover as an indicator of the ice’s climatic “state of health”.

The extent of the ice cover is highly dependent on the wind direction, and short-term changes in the ice cover give very little indication of whether climate change is occurring in the Arctic.

“The dramatic changes in the extent of Arctic sea ice in recent years have mainly been caused by atmospheric circulation patterns that have tended to reduce ice cover, combined with a slow process of climate change. Variations in the circulation patterns are part of the natural fluctuations in the weather. In certain periods these fluctuations will reinforce manmade changes, while at other times they will mask them,” says Mr Sorteberg.

Climate change leads to thinner ice

Mr Sorteberg believes we should be cautious about interpreting the dramatic decrease in Arctic ice cover in the past decade as an indication that the Arctic will be ice free in 10 to 20 years.

However, he emphasises that he and his colleagues do not reject the assertion that climate change is affecting Arctic ice cover or that the IPCC is wrong when it states that the Arctic may be nearly ice free in summer towards the end of this century.

“There is no doubt that the Arctic sea ice has become thinner in recent years. The thickness of the sea ice is a much better indicator than the extent of the ice cover if we want to study how climate change may affect the ice in the Arctic,” said Mr Sorteberg.

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