Half of Greenland and vast areas of Antarctica are destined to melt if global warming continues at the same pace until the end of the century, scientists warned on Thursday.
Their research shows that the loss of so much ice will trigger dramatic rises in sea levels, ultimately swamping low-lying islands and coastal regions and threatening the flood defenses of cities such as London.
The last time so much ice was lost from the poles -- in a period between ice ages 129,000 years ago -- global sea levels rose between 4m and 6m.
Experts believe many coastal regions would suffer long before sea levels rose significantly, because even a minor rise will make storm surges more devastating and increase the risk of flooding.
The warning comes from climate scientists who combined historical records of Arctic and Antarctic ice melting with advanced computer models capable of predicting future environmental conditions.
They found that if nothing is done to put the brakes on climate change, Greenland, the west Antarctic ice sheet and other expanses of polar ice will be warmed beyond a "tipping point" after which their melting is inevitable.
Jonathan Overpeck, director of the Institute for the Study of Planet Earth at the University of Arizona, and Bette Otto-Bliesner, at the US National Center for Atmospheric Research in Colorado, looked back in history to find a time when sea levels were higher than they are today.
They identified a period when glacial melting increased sea levels by several meters.
They used a computer model of the environment to work out how warm the world must have been to trigger the mass melting and concluded that the Earth was between 3oC and 5oC warmer than it is today.
Using the same model, the scientists spun the clock forward to see when climate change is likely to make the world as warm again.
"We showed that that level of warming will come later in this century unless we act on carbon emissions," Overpeck said.
"An Arctic warming of 3oC to 5oC is enough to cause 4m to 6m of sea level rise," he said.
If temperatures do rise as the scientists predict, the ice at the poles will not be lost immediately. Enough ice is likely to melt within the next 100 years to raise sea levels by a meter, but ultimately the fresh water pouring into the North Atlantic would slow down the Gulf stream by a quarter.
"These ice sheets have melted before and sea levels rose. The warmth needed isn't that much above present conditions," said Otto-Bliesner.
The major concern is that unless climate change slows down significantly, the eventual loss of polar ice and subsequent 6m rise in sea levels will become unavoidable.
"There has been an increasing number of observations from the ice sheets suggesting they are responding faster to climate change than anticipated," Overpeck said.
"Now along come our results showing these kinds of changes occurred in the past and lead to large ice sheet retreat and sea level rise," he said.
A 1m rise in the sea level would see the Maldives disappear, make most of Bangladesh uninhabitable and put cities such as New Orleans "out of business," according to Overpeck.
The research was published in two papers in the US journal Science on Thursday.
Tropical Storm Gaemi strengthened into a typhoon at 2pm yesterday, and could make landfall in Yilan County tomorrow, the Central Weather Administration (CWA) said yesterday. The agency was scheduled to issue a sea warning at 11:30pm yesterday, and could issue a land warning later today. Gaemi was moving north-northwest at 4kph, carrying maximum sustained winds near its center of up to 118.8kph and gusts of 154.8kph. The circumference is forecast to reach eastern Taiwan tomorrow morning, with the center making landfall in Yilan County later that night before departing from the north coast, CWA weather forecaster Kuan Shin-ping (官欣平) said yesterday. Uncertainty remains and
SEA WARNING LIKELY: The storm, named Gaemi, could become a moderate typhoon on Wednesday or Thursday, with the Taipei City Government preparing for flooding A tropical depression east of the Philippines developed into a tropical storm named Gaemi at 2pm yesterday, and was moving toward eastern Taiwan, the Central Weather Administration (CWA) said. Gaemi could begin to affect Taiwan proper on Tuesday, lasting until Friday, and could develop into a moderate typhoon on Wednesday or Thursday, it said. A sea warning for Gaemi could be issued as early as Tuesday morning, it added. Gaemi, the third tropical storm in the Pacific Ocean this typhoon season, is projected to begin moving northwest today, and be closest to Taiwan on Wednesday or Thursday, the agency said. Today, there would likely
DISRUPTIONS: The high-speed rail is to operate as normal, while several airlines either canceled flights or announced early departures or late arrivals Schools and offices in 15 cities and counties are to be closed today due to Typhoon Gaemi, local governments announced last night. The 15 are: Taipei, New Taipei City, Taoyuan, Tainan, Keelung, Hsinchu and Kaohsiung, as well as Yilan, Hualien, Hsinchu, Miaoli, Chiayi, Pingtung, Penghu and Lienchiang counties. People should brace for torrential rainfall brought by the storm, with its center forecast to make landfall on the east coast between tonight and tomorrow morning, the Central Weather Administration (CWA) said. The agency issued a sea warning for the typhoon at 11:30pm on Monday, followed by a land warning at 11:30am yesterday. As of
CASUALTY: A 70-year-old woman was killed by a falling tree in Kaohsiung as the premier warned all government agencies to remain on high alert for the next 24 hours Schools and offices nationwide are to be closed for a second day today as Typhoon Gaemi crosses over the nation, bringing torrential rain and whipping winds. Gaemi was forecast to make landfall late last night. From Tuesday night, its outer band brought substantial rainfall and strong winds to the nation. As of 6:15pm last night, the typhoon’s center was 20km southeast of Hualien County, Central Weather Administration (CWA) data showed. It was moving at 19kph and had a radius of 250km. As of 3pm yesterday, one woman had died, while 58 people were injured, the Central Emergency Operation Center said. The 70-year-old