Michael Richardson: Melting ice harbinger of worse to come
https://www.nzherald.co.nz/section/466/story.cfm?c_id=466&objectid=10484020&pnum=0
5:00AM Monday December 24, 2007
By Michael RichardsonAs environmentalists skirmish with Japan over whaling in Antarctic waters, a much bigger issue looms for Antarctica and the world.
Climate change scientists are worried that global warming has reached a tipping point that will trigger a sharp and irreversible rise in sea level, flooding coastal lowlands around the world, destroying homes and property values, and forcing tens of millions of people to move.
The focus of scientific concern is on the rate at which sheet ice, which holds huge quantities of fresh water in the polar caps, is melting.
This formed part of the backdrop of urgency at the recent United Nations climate change negotiations in Bali.
The scientists advising the UN Intergovernmental Panel on Climate Change reported last month that if temperature rise is not reined in, and particularly if it exceeds 2C to 3C, the world could face many species extinctions, widespread starvation as crops fail in hotter, drier climates, and a relentless rise in sea levels that would permanently drown some small island states in the Pacific and Indian oceans.
In their summary for policymakers at the Bali meeting, the scientists noted that the global sea level had risen since 1961 at an average rate of 1.8mm a year, and since 1993 at 3.1mm a year. They said this was partly due to thermal expansion as the sea warmed and partly to water flowing into the sea as sheet ice and glaciers on land melted.The IPCC had previously projected a sea level rise by the end of this century of between 18cm and 59cm. But its latest report cautioned that because understanding of some important causes of sea level rise was too limited, it was not possible to include a best estimate or an upper limit for future sea level rise.
The potential for a global catastrophe is clear. The world's only two continental ice sheets, Antarctica and Greenland, contain over half the total amount of fresh water and around 99 per cent of freshwater ice on Earth. If they melted, the level of oceans and seas would rise by about 64m. Antarctica alone would account for nearly 57m of the rise. The vast ice sheet that entombs nearly all Antarctica also extends offshore as ice shelves. The extent to which Antarctic ice is melting and contributing to rising sea levels around the world is a focus of international polar research this year and next.
Since the IPCC presented its latest report, a scientific team at the University of Colorado in the US has reported that the Greenland ice sheet melted at a record rate this year, the largest retreat since satellite measurements began in 1979.
Greenland is about one quarter the size of the US and about 80 per cent of it is covered by sheet ice. However, Greenland is more susceptible to global warming than Antarctica partly because its climate is strongly affected by proximity to other landmasses and to the North Atlantic, and partly because its ice sheet is smaller and less thick.
Greenland's ice extends over an area of 1.7 million sq km. With an average thickness of 1600m, it has a total volume of about 3 million cu km. This is about one ninth of the volume of the Antarctic ice sheet, which covers 13.6 million sq km, including islands and ice shelves, and has an average thickness of about 2400m. The inland ice has a depth of up to 5000m, making Antarctica by far the highest of the continents.
Scientists writing in a report commissioned by the UN Environment Programme published in June said that summer melting now occurs over about half the surface of the Greenland ice-sheet, particularly near the coast, with much of the water flowing into the sea.
As surrounding temperatures rose, the total loss from the ice sheet more than doubled from a few tens of billions of tonnes a year in the early 1990s to about 100 billion tonnes a year after 2000, with perhaps a further doubling by 2005.
The report warned that Greenland, which has no ice shelves extending out from its coast, provided a picture of Antarctic conditions if the climate warmed enough to weaken or remove protective ice shelves that skirt 1.5 million sq km of the Antarctic coastline.
The questionable stability of Antarctic ice shelves in a warming climate was highlighted by the collapse of the Larsen B shelf in 2002 off the northern Antarctic Peninsula that juts out towards South America. Scientists say the scale of this collapse is unprecedented since the end of the last ice age. Some believe it is a harbinger of worse to come.
* The writer, a former Asia editor of the International Herald Tribune, is a security specialist at the Institute of Southeast Asian Studies in Singapore.
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