A warmer Md. will be wetter

Threat from climate change takes form of land submersion, severe storm damage

February 03, 2007|By Tom Pelton and Dennis O'Brien | Tom Pelton and Dennis O'Brien,Sun reporters

By 2100, Baltimore's Harborplace could be under water at high tide. Ocean City might be frequently evacuated because of Atlantic storms. Hooper and Smith islands in the Chesapeake Bay could join 13 others that have been submerged in the estuary.

Across Maryland, almost 1,000 square miles of coastal land are threatened by rising sea levels, scientists warn.

These are a few of the local effects of global warming that researchers are discussing in the wake of a new report by a United Nations panel. More than 2,500 scientists from 130 countries in the Intergovernmental Panel on Climate Change predict that sea levels will rise by up to two feet over the next century.

This figure is lower than a 2001 estimate of as much as a three-foot rise.

But scientists in the Chesapeake region took little comfort in that, in part because land in this area is also sinking at a rate of about seven inches a century - making it a particularly vulnerable area.

Donald F. Boesch, president of the University of Maryland Center for Environmental Science, said the most recent U.N. summary of the state of scientific consensus probably underestimates the rate of sea level rise. He said it doesn't take into account more studies over the past few months that suggest that the Greenland ice sheet and parts of Antarctica might be melting faster than previously thought.

"It's not reassuring," Boesch said. "If I were a prudent person, I would plan for a 2- to 4-foot rise in sea levels in the Chesapeake Bay. But be prepared for the possibility of much more shocking rates of polar ice melt, which could raise sea levels by five or even six feet this century."

The damage caused by rising water levels is magnified during storms, when winds drive surges of water up the Chesapeake Bay and other waterways. Tropical Storm Isabel in 2003, for example, drove a seven-foot storm surge into downtown Baltimore, flooding the Harborplace retail complex and nearby blocks.

That kind of flooding could become common at the busy corner of Pratt and Light streets - not just during storms but several times a year during normal high tides, Boesch said.

"There are several options, and one is to build sea walls," Boesch said. "The other alternative is to retreat to higher ground."

The scientific panel predicts in its most recent report that global sea levels will rise by seven inches to 23 inches by 2100. Average global temperatures could climb by up to 8 degrees over that time.

Using language stronger than in a 2001 report that summarized scientific consensus, the panel said it was more than 90 percent sure - having "very high confidence" - that global warming is being caused by human industry.

The burning of coal and oil is releasing carbon dioxide and other greenhouse gases that are thickening an insulating layer around Earth, raising temperatures, melting glaciers and swelling the oceans.

The report says it's "more likely than not" that hurricanes and storms are growing in ferocity because of the higher ocean surface temperatures.

Bruce Douglas, a Bethesda-based geophysicist, said the problem of rising waters is compounded in Maryland and Delaware because the land here is sinking.

Vast ice sheets that covered much of North America 20,000 years ago pressed down on what is now Canada and some of the northern United States, causing a protrusion of the planet's mantle that has been subsiding ever since.

This sinking makes the area "vulnerable to storms, and we're going to be losing wetlands at an even faster rate" than otherwise, said Douglas, who recently retired from the National Oceanic and Atmospheric Administration.

Douglas, now a research professor at Florida International University who lives in Bethesda, said rising seas also cause beach erosion. For every foot of sea level rise, 50 to 100 feet of beach is washed away, he said. The damage is under way, with about 580 acres of coastal land being lost each year, according to the Maryland Department of Natural Resources.

The rising sea will not inundate most areas of the state, even on the low-lying Eastern Shore. The Cambridge Airport, for example, is 19 feet above sea level. But it will make waterfront areas and many low-lying communities more susceptible to damage from severe storms, Douglas said.

Michael Kearney, a professor of geography at the University of Maryland College Park, predicted that the state could lose most of its wetlands over the next century.

"Hooper Island probably will be gone," Kearney said of the narrow peninsula lined with homes in Dorchester County. "The north end of Assateague Island would be gone. Smith Island would be gone. ... The possibility that any of these islands in the Chesapeake Bay being still inhabited is very low."

Zoe Johnson, coastal planner for the Maryland Department of Natural Resources, said that the state is encouraging counties on the Eastern Shore to revise their building codes to deal with inevitable flooding.

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