| 
  • If you are citizen of an European Union member nation, you may not use this service unless you are at least 16 years old.

  • You already know Dokkio is an AI-powered assistant to organize & manage your digital files & messages. Very soon, Dokkio will support Outlook as well as One Drive. Check it out today!

View
 

Sea Level Rise calculations

Page history last edited by PBworks 15 years, 6 months ago

Source: The Guardian.

 

Sea level rises may accelerate due to melting ice sheet.

 

By the end of the century sea levels may be rising three times as fast

as they are at present, as a result of rapid melting of the Greenland

ice sheet

 

The vast Greenland ice sheet could begin to melt more rapidly than

expected towards the end of the century, accelerating the rise in sea

levels as a result of global warming, scientists warned yesterday.

 

Water running off the ice sheet could triple the current rate of sea

level rise to around 9mm a year, leading to a global rise of almost 1

metre per century, the researchers found.

 

Sea levels are already on the rise as a result of increasing

temperatures, because the oceans expand as they warm up, but until now

scientists have had a poor understanding of how quickly ice sheets

such as those in Greenland and Antarctica will begin to disappear.

 

There are signs that the Greenland ice sheet, which covers 1.7 million

square kilometres of land, has already begun to melt faster than

expected. The reason is thought to be surface water on the ice sheet

trickling down through fissures to the underlying bedrock, making the

ice sheet less stable, and the loss of buttressing ice shelves along

the coastline.

 

Climate scientists are uncertain how susceptible ice sheets are to

global warming, largely because they have never witnessed one

disappear, so researchers led by Anders Carlson at the University of

Wisconsin-Madison decided to look back to the end of the last ice age

for clues.

 

Around 20,000 years ago, when the last ice age was at its peak, a

giant mass of frozen water called the Laurentide ice sheet covered

much of what is now North America. The ice sheet, which was three

miles thick in some places, had almost completely melted 6,500 years

ago as the world warmed as part of its natural cycle. At the time,

surface air temperatures were similar to those that climate scientists

predict for 2100.

 

The researchers used evidence in the geological record and computer

simulations to reconstruct the demise of the Laurentide ice sheet,

which was the last ice sheet to completely disappear in the northern

hemisphere.

 

They dated boulders and fossilised organisms left on fresh ground as

the ice sheet retreated, and found that it went through two periods of

rapid melting. Computer simulations revealed that around 9,000 years

ago, water melting off the ice sheet caused sea levels to rise by

about 7 metres at a rate of around 1.3cm a year. The second stage of

rapid melting began 7,500 years ago, when sea levels rose by 5 metres

at a rate of around 0.7cm a year.

 

The reconstruction suggests that the Greenland ice sheet may melt in a

similar fashion. "We have never seen an ice sheet retreat

significantly or even disappear before, yet this may happen for the

Greenland ice sheet in the coming centuries to millenia," said

Carlson, whose study appears in the journal Nature Geoscience.

 

"We're not talking about something catastrophic, but we could see a

much bigger response in terms of sea level from the Greenland ice

sheet over the next 100 years than what is currently predicted,"

Carlson added.

 

The most recent report from the UN's Intergovernmental Panel on

Climate Change predicts that sea levels will have risen by around 10cm

at most by 2100, but according to Carlson's analysis, rapid melting of

the Greenland ice sheet could cause much greater rises.

 

"For planning purposes, we should see the IPCC projections as

conservative," he said. "We think this is a very low estimate of what

the Greenland ice sheet will contribute to sea level."

 

In an accompanying article, Mark Sidall at Bristol University

describes how a 1 metre rise in sea level would submerge an estimated

2.2m square kilometres of land, largely in Asia, and displace around

145 million people at a global cost of $944 billion.

 

He points out, though, that while the Laurentide ice sheet completely

vanished at the end of the last ice age, the Greenland ice sheet

remains, suggesting it is more resistant to warming. "To what extent

this dynamic response of the Laurentide ice sheet to past temperature

change can be considered analagous to present and future reduction of

the Greenland ice sheet remains unresolved," he writes. "But [the

researchers'] work suggests that future reductions of the Greenland

ice sheet on the order of 1 metre per century are not out of the

question."

 

 

posted by Ross Mayhew to ClimateConcern

Comments (0)

You don't have permission to comment on this page.