Least sea ice in 800 years

Biology News

Current extent of sea ice

Svalbard and Fram Strait - Map of study area Map: Norman Einstein

Svalbard Vista

There are of course neither satellite images nor instrument-based records of the climate all the way back to the 13th century, but nature has its own record of climate change for those who know where to look for it, and there are in fact human-made records that contain a lot of relevant information — such as observations in the log books of ships and in harbor records. Piece all of the information together and you get a picture of how much ice there has been at any given time during the last eight centuries.

Modern research and historical 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.

To find out how much sea ice there has been, the researchers looked at data from the logbooks of ships, among other sources. These logs, which go all the way back to the 16th century, tell the exact geographical position of the ice boundary in past eras. Icelandic harbor records also provided significant information.

By combining their climate curve with the data from historical records, the researchers were able to reconstruct the extent of the 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 ice as in the 20th century.

In the middle of the 17th century there was also a sharp decline in the ice, but it lasted only a very short time. The greatest cover of sea ice was during the next century, a period known as the 'Little Ice Age'.

"There was a sharp change in the ice cover at the start of the 20th century," explains Aslak Grinsted. And that change has continued —"We see that the sea ice is shrinking," he says, "to a level which has not been seen in more than 800 years."

Time at last to search for a Northwest Passage?