Global warming could cause the world's ice sheets and glaciers to melt with alarming results: tidal waves and rises in sea levels.
Another fear of international climate scientists is that the disappearance of large quantities of ice means the planet could warm up more quickly because 80% of the heat and light of the sun is reflected back into space from ice or snow.
Ice shelves cover 50% of the Antarctic coast. The surface area of all ice shelves together is more than one-tenth the size of the continent. The largest individual shelf is the Ross ice shelf in West Antarctica, also called the Great Ice Barrier. It is as big as France. Ice shelves float up and down with the tides, grating against the rocks and eventually breaking apart. Every year, the edges of ice shelves break off, or calve, into icebergs as a result of seasonal warming. During normal years, the total mass of calvings is an extremely small percentage of the ice cap, and the ice lost through calving equals the mass of snowfall on the continent. During the past few years, ice shelves on the Antarctic peninsula have been quickly melting. Some scientists fear that the region has now entered a vicious cycle of polar warming, with rising average temperatures, fewer cold years and longer summer melting, resulting in the warming of Antarctica's waters.
It was reported in 1993 that ice cover in Arctic regions decreased over the past four decades. These decreases are statistically significant for the summer seasons and consistent with regional temperature trends.
NASA scientists said that the rate at which the huge Greenland ice sheet was melting had increased by a fifth between 1980 and 2000. This is because more melt-water is trickling down from the surface of the sheet to the bedrock 1,200 meters below. The water 'lubricates' the path of the whole sheet, causing it to slip faster towards the sea, a process had never before been detected in large ice sheets. It is predicted that accelerated seasonal melting around the North Pole could allow routine commercial shipping through the North West Passage for one month a year from 2010. The Northern Sea Route across the top of Russia could allow shipping for at least two months a year as soon as 2005. The new routes would cut the distances for voyages between Europe and East Asia by a third and open up new fisheries. The resulting boom in shipping could lead to conflicts, as nations try to enforce fisheries rules, prevent smuggling and piracy and protect the Arctic environment from oil spills. To complicate matters, Russia and Canada consider their northern sea routes as national territory, while the US regards them as international waters.
We assume that global warming is under way now and it may be enhanced by human activities, but until now its effect on ice loss in Greenland and the Antarctic has been mostly speculation.
Fluctuations in ice cover in at least some Arctic regions may be influenced by interdecadal fluctuations in land run-off and hence surface water salinity, with high run-off periods inducing larger sea ice extent.