The Arctic Sea Ice Is Melting--How Long Will It Last?
This page was last revised on May 25, 2000.
There has been a lot of press lately about icebergs breaking off Antarctica's ice shelves
and the effects this will have on sea levels around the world. There has been much less press about a potentially more significant change in polar ice near the other pole, where Arctic Ocean sea ice
is rapidly melting. The lack of coverage is somewhat understandable because the changes in the Arctic sea ice are less visible and less dramatic. Most of the reduction in the ice is in its thickness, which can only be measured with submarine sonar equipment. Also, since sea ice is floating ice, its melting won't have much effect on sea levels.
However, melting of the Arctic sea ice will have a dramatic effect on the albedo (reflectivity) of the Earth's
surface in the Arctic region. The lower albedo of open ocean will mean less solar energy reflected back into
space. It will instead be absorbed by the ocean. The warmer water will melt more sea ice, and eventually the
warmer atmosphere above the warmer water will melt more of the ice sheets on Greenland. Since sea ice and
sheet ice both consist of fresh water, the result will be a huge increase in the amount of fresh water in the Arctic Ocean. This could possibly lead to a shutdown of the North Atlantic thermohaline circulation
and drastic cooling of temperatures everywhere.
Reporting in Geophysical Research Letters, Rothrock et al presented compelling evidence of the reduction in
thickness of Arctic sea ice over the past 40 years. Combining their data with data from another study on the extent of Arctic sea ice
, it would appear that the total mass of sea ice has shrunk by up to 60% in the past 40 years.
Extrapolation of the Rothrock et al data indicates that sea ice in the Eastern Arctic Ocean could be entirely gone by September 2001. See the table below. According to a US Navy ice thickness computer model, the extrapolations in the table are about right. For example, the table indicates a thickness of 2.1 meters for the
North Pole region for September 1999 whereas the US Navy model indicated a thickness of 1.8 to 2.4 meters. See the graphic below the table.
Anecdotal evidence suggests that the sea ice may be melting even faster than indicated in the table. The evidence was reported in the London Evening Standard
on Wednesday, May 17, 2000: "Two Royal Marine commandos walked onto the North Pole this morning. Their feat had been a race against time as approaching
bad weather meant they were to be airlifted out today whether they had reached the Pole or not. In addition,
the thinning ice meant there was a very narrow weather window available to land a plane. As they were retrieved the temperature was a mere -1C, compared to the -55C they encountered through the rest of the
journey...Five adventurers were rescued from the North Pole on Monday after their plane broke through melting ice and sank."**
According to the US Navy computer model, the thickness of the sea ice reaches its annual maximum during
the month of May. It reaches its annual minimum (about one meter less) in September. The daily extent of Arctic sea ice may be monitored at the NOAA/OMB Sea Ice Analysis Page
. The simulated thickness of Arctic sea ice may be monitored at the US Navy Monthly Models web site. Click on the month you want,
then click on Section 4.3 Arctic Ice Thickness, then click on Figure 4.3.
**Special thanks to Alastair McDonald on the uk.sci.misc newsgroup for this reference, and for help in
interpreting the data in the Rothrock et al paper.