PHOENIX (By Shaun McKinnon, Arizona Republic) March 24, 2006 — Global temperatures are climbing at a rate that will melt ice sheets in Greenland and Antarctica before the end of this century, a disaster that could raise sea levels and scramble weather patterns across the planet, according to a new study.

Roiling oceans would redraw coastlines from Cape Cod to New Orleans, threatening low-lying cities with rising sea levels. Arizona and the West would grow hotter and drier, with shorter winters that would produce less runoff and further stress water supplies.

Even the scientists who framed that scenario in the study on global warming admit they were surprised at its grimness, taken aback by how rapidly the melting could accelerate. Moreover, they say, much of what the studies predict is already here: Temperatures are rising, sea levels are inching higher and warmer oceans are playing havoc with weather.

Their research is outlined in two articles published today in the journal Science. The articles add more voices to an often-discordant debate over global warming and its effect on climate and the oceans.

Some critics have dismissed it as junk science and have produced data that they say show temperatures are starting to fall. Others question whether human-caused pollutants are to blame for rising temperatures, as many scientists argue.

Researchers in the latest studies believe humans do play a role and say there is time to avert the worst effects if world powers are willing to reduce greenhouse gases and other pollutants believed to contribute to warming. But at a yet-to-be-determined point midway through the century, the process will become irreversible.

"We now know enough in advance to stop it from happening," said Jonathan Overpeck, one of the chief researchers on the project and director of the University of Arizona's Institute for the Study of Planet Earth. "If we let it go another couple of decades, we could be in real danger of crossing the threshold."

The studies, one led by Overpeck, the other by Bette Otto-Bliesner at the National Center for Atmospheric Research, examined climate data dating back about 130,000 years, a time between two ice ages.

Shifts in the Earth's tilt and orbit led to warmer conditions in the Arctic. Temperatures rose 5 to 8 degrees Fahrenheit, melting wide swaths of Greenland's ice sheet. The melted ice raised ocean levels as much as 11 feet, the scientists believe.

But natural climate records, including evidence from ancient coral reefs, sediments and fossils, indicate sea levels actually climbed by as much as 20 feet in that period, more than what the Greenland ice sheet could account for. Overpeck theorized that disintegrating ice sheets at the Antarctic were responsible for the difference.

His research suggests the rise in sea levels caused by Arctic warming and melting probably destabilized Antarctic ice shelves, which are more vulnerable than Arctic ones.

"To get rid of Greenland's ice, you have to melt it," Overpeck said. "In the Antarctic, all you have to do is break up the ice sheet and float it away, and that would raise sea level. It's just like throwing a bunch of ice cubes into a full glass of water and watching the water spill over the top."

The scientists believe the process could occur more quickly today because of global-scale year-round warming. Temperatures are rising in both the Northern and Southern hemispheres. Man-made pollutants could hasten melting by darkening the ice and snow, allowing it to absorb more sunlight, the studies say.

"The implications are global," Otto-Bliesner said. "These ice sheets have melted before, and sea levels rose. The warmth needed isn't that much above present conditions."

What made the findings more urgent is how closely the predictions match trends in global climate and ocean conditions, Overpeck said.


• Temperatures have been steadily rising over the past decade. Nine of the 10 warmest years on record have occurred since 1995. The UA study predicted the Earth's temperatures will rise by at least 4 degrees by 2100, which would be comparable to conditions 130,000 years ago, when the ice sheets melted.

Even a 1-degree rise in temperature is significant on a global scale. Such changes are usually measured in fractions of a degree.

"The Arctic is already warming much faster than we thought it would," Overpeck said. "To think we're not going to get 4 to 5 degrees warmer in another 50 years is wishful thinking."


• Sea levels are rising more rapidly, in part due to thermal expansion of the ocean waters caused by the worldwide rise in temperatures, he said. That expansion didn't occur 130,000 years ago because the warming was more localized.

By the end of this century, sea levels could rise 3 to 4 feet; if current warming trends continue, "we're committed to 4 to 6 meters (13 to 20 feet) in the future," Overpeck said.

The implications for heavily populated U.S. coastlines are ominous. The scientists produced images that show wide areas of the upper Eastern Seaboard underwater if oceans rise as high as they once did. The Florida and Gulf coasts would be eaten away, exposing cities such as New Orleans to crippling storm surges more often. The effects would gradually spread as sea levels caught up to the melting ice sheets.

• Rising ocean temperatures are blamed for volatile weather worldwide and are believed to be a contributor to Arizona's drought, now in its 11th year. Melting ice sheets could worsen those trends.

"Arizona's in front of the line to get hammered by this. It's going to make our state drier: hot and drier," Overpeck said. "That's bad for natural vegetation and bad for water supplies. We'll see a lot less snow."

Several studies have concluded that climate change will shorten winters across the West, reducing the amount of snow that falls and the flow of water into rivers and reservoirs.

But Overpeck and other scientists are convinced it's not too late. To slow warming, federal and state officials would have to impose strict limits on emissions of greenhouse gases. They also would need to demand energy conservation and step up use of wind, solar energy and advanced biofuels.

"The knowledge we need to implement these things is already developed or close to being developed," Overpeck said.

He lauded efforts by individual states to address climate change, but he acknowledges that not everyone agrees on the solution or even the problem. He said corporate interests with a stake in the status quo have enlisted scientists to "make it sound like these things are less certain than they really are."

"People also think we have to make big changes, that there's not much we can do," Overpeck said.

"There's lots we can do. With every year that goes by, there are new technologies. The biggest problem humankind has ever faced is something we can deal with, but it takes a national will to act."