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All about the world's ice
By Jack Williams, USATODAY.com
At the beginning of the 20th century, the world's attention turned to the polar regions as explorers raced to be first to reach the North Pole and then the South Pole.
Going into the 21st century, the Arctic and Antarctic are the focus of scientific attention because they hold answers to questions about the Earth's past, present and future climate.
You often hear the question: Is polar ice melting?
The answer that that is, "Yes, it is melting." But, you could have said the same thing during the height of any of Earth's ice ages.
Polar ice is always melting, and also always growing as more snow falls that doesn't melt during the summer.
The real question: "Is polar ice melting faster than new ice is being added?"
This is the question that scientists by studying the Earth's largest ice sheets in Antarctica and Greenland. One of the largest such studies is the ongoing West Antarctic Ice Sheet Initiative. (Related story: Answers to sea level rise locked in ice)
If all of these two ice sheets melted sea levels would rise by about 215 feet all over the world. Fortunately, even the most extreme global warming scenarios don't see this happening for centuries. Greenland's ice is probably in the most danger of melting, and this would raise global sea levels by about 21 feet. Scientists who study the ice don't think this is likely during the life of anyone alive now.
The figures above come from the U.S. Geological Survey's estimate of how much ice is locked up in the world's ice sheets and glaciers and how much sea level would rise if they melted. (Related document: Estimated area and volume of global ice)
Not all ice is near the poles
While most of the world's ice is in the Arctic and Antarctic, quite a bit is scattered around the Earth in the form of glaciers. Not all of these are in cold places, such as Alaska.
Several glaciers are in the tropics, but they are on tops of high mountains.
Smaller glaciers around the world are melting, however, and this is causing some sea-level rise. (Related: Glaciers vanishing around the world)
What's likely in a warming world
While all scientists who study polar ice don't agree on how much is likely to melt if the world continues warming, the January 2001 report of Working Group 1 of the Intergovernmental Panel on Climate Change (IPCC) offers the best summary of the latest scientific thinking. This group consisted of experts from around the world and looked at the basic science of climate change.
In its Summary for Policy Makers, the working group says on that during the 21st century:
· Northern Hemisphere snow cover and sea-ice extent are projected to decrease further.
· Glaciers and ice caps are projected to continue their widespread retreat during the 21st century.
· The Antarctic ice sheet is likely to gain mass because of greater precipitation, while the Greenland ice sheet is likely to lose mass because the increase in runoff will exceed the precipitation increase.
· Concerns have been expressed about the stability of the West Antarctic ice sheet because it is grounded below sea level. However, loss of grounded ice leading to substantial sea level rise from this source is now widely agreed to be very unlikely during the 21st century.
· Global mean sea level is projected to rise by 0.09 to 0.88 meters (0.29 to 2.88 feet) between 1990 and 2100.
The report notes that projections of sea level rise are lower slightly lower than in the Working Group's 1995 report even though the 2001 report projects higher temperatures by 2100 than the 1995 report did. The reason is "primarily due to the use of improved models, which give a smaller contribution from glaciers and ice sheets" than the models used for the 1995 report. (Related document: IPCC