Polar ice sheets are melting faster than most authorities realize and could eventually submerge coastal communities worldwide, according to a pair of studies released today.
Researchers from the University of Arizona and the National Center for Atmospheric Researchers noted that sea levels rose 20 feet during a warming period 129,000 years ago - and said the waters could rise just as high sometime after 2100 if global temperatures continue to climb.
Maryland would be hit harder than most areas, with the Eastern Shore particularly vulnerable, said J. Court Stevenson, a professor at the University of Maryland Center for Environmental Sciences at Horn Point, who was not involved in the studies published today.
"We're talking about our grandchildren having to face this," he said.
Scientists have been warning for decades that carbon dioxide and other "greenhouse" gases from power plants and vehicle exhaust are warming the planet and raising the seas. They say the best way to minimize the damage is to drastically reduce smokestack and tailpipe emissions.
While some researchers dispute specific aspects of global warming, more than 2,000 scientists from 100 countries who served on the Intergovernmental Panel on Climate Change concluded in 1995 and 2001 that global warming is real and that carbon dioxide produced by humans is largely to blame.
And the two studies published today in the journal Science argue that the impact of melting from Antarctica's ice sheets has been underestimated.
That melting will exacerbate the effects of global warming and play a major role in submerging many coastal communities if nothing is done to curb the emissions, the researchers say.
No one is sure of the extent of the melting or the timing of its effects. But the researchers say that with the warming climate, melting ice sheets in Greenland, the Arctic and Antarctica could inundate coastal areas around the world.
Maps released with the studies show extensive coastal areas in Florida, New Orleans and Cape Cod that the researchers say might one day be submerged.
"As Katrina pointed out, we only need a meter of sea level rise to make much of New Orleans unlivable. The same goes for a number of coastal areas," said Jonathan T. Overpeck, a geosciences professor at the University of Arizona and lead author of a study.
In Maryland, rising sea levels are washing away islands in the Chesapeake Bay and threatening hundreds of homes, roads and businesses, said Stevenson, who has been studying the regional effects of rising sea levels since the 1980s.
A gauge at the Inner Harbor show a one-foot rise in sea level over the past 100 years. More recently installed gauges in Solomons, Cambridge and Annapolis show that waters in those areas are rising even faster, he said.
The hardest-hit areas in the decades to come will be Talbot, Somerset, Dorchester, Worchester and Wicomico counties, Stevenson said. The seas are expected to rise slowly and steadily, but no one knows how soon or by how much, he said.
Stevenson began looking into sea levels in the 1980s when he found that rising water had washed away at least 3,000 acres of the Blackwater National Wildlife Refuge since the 1930s.
"We're in probably the most dangerous zone for sea level rise," he said. "This is not a trivial story and it's not a trivial problem."
When he published papers in the mid-1980s, colleagues were reluctant to accept his findings, he said.
For many scientists, this is hardly news: two years ago the Maryland Department of Natural Resources and the U.S. Geological Survey began releasing maps, based on aerial photography and computer models, showing low-lying areas on the Eastern Shore most susceptible to rising seas.
Before that, in a 2001 report, the International Panel on Climate Change, a group of world experts assessing the effects of warming, also said sea levels could rise up to three feet over the next century.
Earth's average temperature has increased about 1 degree Fahrenheit over the past 30 years, a relatively rapid rise, scientists say, and sea levels are rising about an inch each decade.
The seas have risen and fallen significantly since Earth was formed more than 4 billion years ago. Sea levels rise and fall based on long-term climate patterns and the amount of ice in polar ice sheets, experts say.
But by focusing on a particularly warm stretch 129,000 years ago, the researchers say they found how much sea levels will rise as temperatures continue to climb.
"We estimate the high end is three feet per century, but it could be faster," Overpeck said.
Ice cores and ancient sediments show a 20-foot rise in sea levels during the warm stretch 129,000 years ago, a period known as the Last Interglaciation.
The seas rose because of melting ice in Greenland and in the Arctic, as well as the melting of two Antarctic ice sheets. The impact of the Antarctic ice sheets had been previously underrated, the researchers say.
"I was really surprised at the amount of sea level rise and how little warming you need to get to it," Overpeck said.
The difference between warming now and 129,000 years ago is that the ancient temperature increases were caused by deviations in the tilt of the Earth's axis and its orbital pattern, which affected the amount of sunlight warming the planet, said Bette Otto-Bliesner, a climate expert at NCAR and lead author of the other study. Future warming is expected to be the result of carbon dioxide and other greenhouse gases emitted from tailpipes and smokestacks, she said.
The researchers projected increases in carbon dioxide levels from today's 380 parts per million to 1,060 by 2100, a change forecast by the International Panel on Climate Change. The researchers say that they used the mid-range of carbon dioxide increases included in the IPCC 2001 report.
Based on that forecast, they say summer Arctic temperatures will jump by 4 to 8 degrees Fahrenheit by 2100.
Overpeck said he has spent five years discussing various parts of his study with other experts at scientific conferences. "We really wanted to make sure we got everything right," he said.
Experts say the report is another warning signal about the effects of global warming. "I live on Cape Cod, so I guess I'll be moving," joked Karen Bice, a paleoclimatologist who studies past climates at the Woods Hole Oceanographic Institute.
Bice's research shows that many of the computer models used to assess warming - including the NCAR model used by Overpeck and Otto-Bliesner - underestimate the effects that greenhouse gases will have on temperature and sea level increases. The seas could rise even more than 20 feet, but how soon that happens is difficult to estimate, she said.
"Either way, it's a lot of sea level rise. There's no question, it's a lot," Bice said.
The studies, funded by the National Science Foundation, are among several recent reports that used satellite imagery, ice cores and geological records to measure the effects of warming on glaciers and ice sheets.
A NASA study last month showed substantial melting of Greenland's glaciers, and a University of Colorado study published earlier this month found substantial melting in Antarctica.
The Goddard Institute of Space Studies released a report in January showing that last year was the warmest year on record. A NASA study released in September showed less sea ice floating in the Arctic Ocean than at any time in the past century.
The Bush administration, which has often been criticized for not taking enough steps to address warming, declined to discuss the studies published yesterday.
While other nations have signed the Kyoto Protocol, which pledges mandatory steps to reduce greenhouse gas emissions, Bush has steadfastly refused to commit the United States, relying instead on voluntary measures.
Michele St. Martin, a spokeswoman for the White House Council on Environmental Quality, said in a prepared statement that the Bush administration is spending $2 billion for climate research and science programs and that the recent studies are an example of how the funds are helping enhance "knowledge about the Earth's climate and the way it has evolved and changed over time."