Sea Ice July 2009

The areal extent of the sea ice was around a half million square kilometers larger this year than it was over the past four years. However that has abruptly changed and it is almost as low now as 2007. Most interesting this year is that Davis Strait is wide open already and it is also way ahead on the Eastern side by Russia.

What appears different this year to this observer is that the polar ice seems more intact for the moment. That means to me that the Northwest Passage may stay sealed. No bets yet.

The period of maximum attack on the ice has begun and it will be interesting to see just how much it opens up.

Do recall that it was reported much thinner than expected earlier this spring, so these pictures may be misleading.

I will say however, that it is very vulnerable to wind activity.

I notice that I can sail deep along the north coast of Greenland for the first time and that Lancaster is already wide open until you hit the end of Ellesmere.

The attached report is important because it discounts the extent of sea ice decline during the medieval warm period. That may be because of proxy failure rather than reality. However, the strong warming in the early part of the twentieth century kicked of an ongoing cycle of ice retreat with modest recoveries. Therefore the net loss over each cycle is positive for one century.

Up to this point, I was only comfortable that that held true for the past three decades or so. Our present decade is only slightly cooler than the past decade, but it is apparent that the trend line on ice loss is still positive.

We are set up right now, should weather cooperate, for another sharp decline in ice thickness this year, at a time in which there is much less to work with. Again the remarkable and unexpected thinness this spring is remarked.

I hate to say this, but we are on track for open water around the pole in 2012. Nothing has reversed the established trend, and this item has established that the condition has persisted over a whole century and losses now are quite visible and reflect expectations of final breakup.

The Least Sea Ice In 800 Years

by Staff Writers
Copenhagen, Denmark (SPX) Jul 03, 2009

New research, which reconstructs the extent of ice in the sea between Greenland and Svalbard from the 13th century to the present indicates that there has never been so little sea ice as there is now. The research results from the Niels Bohr Institute, among others, are published in the scientific journal, Climate Dynamics.

There are of course neither
satellite images nor instrumental records of the climate all the way back to the 13th century, but nature has its own 'archive' of the climate in both ice cores and the annual growth rings of trees and we humans have made records of a great many things over the years - such as observations in the log books of ships and in harbour records. Piece all of the information together and you get a picture of how much sea ice there has been throughout time.

Modern research and historic records

"We have combined information about the
climate found in ice cores from an ice cap on Svalbard and from the annual growth rings of trees in Finland and this gave us a curve of the past climate" explains Aslak Grinsted, geophysicist with the Centre for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen.

In order to determine how much sea ice there has been, the researchers needed to turn to data from the logbooks of ships, which whalers and fisherman kept of their expeditions to the boundary of the sea ice. The ship logbooks are very precise and go all the way back to the 16th century.

They relate at which geographical position the ice was found. Another source of information about the ice are records from harbours in Iceland, where the severity of the winters have been recorded since the end of the 18th century.

By combining the curve of the climate with the actual historical records of the distribution of the ice, researchers have been able to reconstruct the extent of the sea ice all the way back to the 13th century. Even though the 13th century was a warm period, the calculations show that there has never been so little sea ice as in the 20th century.

In the middle of the 17th century there was also a sharp decline in sea ice, but it lastet only a very brief period. The greatest cover of sea ice was in a period around 1700-1800, which is also called the 'Little Ice Age'.

"There was a sharp change in the ice cover at the start of the 20th century," explains Aslak Grinsted. He explains, that the ice shrank by 300.000 km2 in the space of ten years from 1910-1920. So you can see that there have been sudden changes throughout time, but here during the last few years we have had some record years with very little ice extent.

"We see that the sea ice is shrinking to a level which has not been seen in more than 800 years", concludes Aslak Grinsted.

No comments:

Post a Comment