Friday, July 20, 2007

Global Warming Threatens Chesapeake Bay

The Washington Post reports:

Climate change has already begun to alter the Chesapeake Bay, warming and raising its waters in a way that could unbalance delicate ecosystems and doom low-lying islands, according to a report released yesterday by the Chesapeake Bay Foundation.

The report, citing scientific research from around the bay, sketched a prognosis that was troubling even by the standards of the Chesapeake -- a beautiful but polluted estuary that environmentalists have spent decades trying to save.

It found that some of the bay's oldest problems, such as low-oxygen "dead zones," could get worse as the bay's water slowly warms. And, the study found, new problems are cropping up, as key plants and animal species show signs that they are uncomfortably warm.

"We know that the bay is in trouble today, and we know that climate change will make the bay worse in the future," said William C. Baker, president of the foundation, an environmental group based in Annapolis.

The report said warming temperatures could be forestalled by cutbacks in emissions of carbon dioxide and other greenhouse gases. Some of the measures proposed to clean up the bay's water could actually help in this effort, it said. One example was the planting of forested buffers along streams. These filter pollution out of runoff, and also provide trees to absorb carbon dioxide from the air, the study said.

Yesterday's report summarized what bay scientists have been learning over the last decade: The Chesapeake seems to showing the first signs of impact from a warming climate. The changes might not seem drastic. Since 1930, the average water temperature off Solomons Island has risen by about 2 degrees. The bay's water rose about a foot in the last century.

But shifts like these can have sweeping consequences, scientists say, for both the wildlife in the bay and the people living around it.

Warming water, for instance, is a problem because the Chesapeake's ecosystem is a blend of southern, heat-tolerant species, and cold-tolerant ones whose real heartland lies farther north. When water heats up, cold-tolerant species can suffer.

One prime example, cited in yesterday's study, is an underwater plant called eelgrass that provides crucial habitat for animals such as blue crabs. It cannot live long in water much warmer than 80 degrees. During a long warm spell in the summer of 2005, huge tracts of eelgrass were wiped out.

"In the fall, basically what we saw was nothing," said Robert Orth, a professor at the Virginia Institute of Marine Science who surveyed areas where the grass had been. "The plants basically just totally died."

In the two summers since, Orth said yesterday in a telephone interview, some of the eelgrass has grown back. But he said he fears what could happen if temperatures warm in the future. A recent study by a commission of the United Nations predicted that global temperatures might increase by 0.7 degrees by 2027.

"If you have two back-to-back really hot years," Orth said, "you could lose all the eelgrass in the bay."

Yesterday's report also cited striped bass -- one of the bay's most beloved fish for food and sport -- as a creature under pressure from the heat. Foundation officials said the bass, also called rockfish, cannot tolerate water temperatures much above 76 degrees.

But when the water near the surface gets that hot, they sometimes cannot dive to cooler water because, as a result of the bay's existing pollution problems, there is often little oxygen at lower depths.

"It's like the old horror movies where the floor is rising, and the ceiling is lowering," Baker said. "They're getting squeezed."

Though many of yesterday's predictions were dire, scientists say it is exceedingly difficult to forecast exactly what the future will bring for a system as complex as the bay. Its health depends on a tangle of factors: development across the massive Chesapeake watershed, changes in temperature and rainfall, currents and winds that stir the water.

That makes it hard, for instance, to say precisely what will happen with the bay's dead zones. Foundation officials said yesterday that they believed hotter weather would make them worse.

Dave Jasinski, a water-quality analyst at the University of Maryland Center for Environmental Science, said climate change could cause changes across the bay and its watershed. "I don't know that anybody has any conclusive idea" what all the changes would add up to, he said.

Another problem laid out in the report is that as temperatures increase, global sea levels are expected to rise 7 to 23 inches by 2100. The rise is expected to be more severe in this area because land around the Chesapeake is slowly sinking, thanks to a complex geological process that began after the last Ice Age.

On low-lying Smith Island, in the Maryland section of the bay, waves are now just a quarter-mile away from the village of Rhodes Point, said Rick Edmund, the minister of Smith Island's three Methodist churches. He said residents are hoping Congress will approve a $9.4 million plan, proposed by Sen. Benjamin L. Cardin (D-Md.), to build artificial breakwaters offshore.

But Edmund said island residents know that their problems will probably get worse.

"Climate change," he said in a telephone interview yesterday, "will get us in the long run."