Sea levels in the Chesapeake Bay have risen a foot during the 1900s and may rise another 3 feet during the next century because of global warming, a University of Maryland scientist said yesterday.

Dr. Michael S. Kearney, a coastal geographer at the College Park campus, reported that some bay islands have disappeared within recent decades and vulnerable waterfront on the Eastern Shore is losing as much as 10 feet of shoreline a year.

"You don't have to look very far for evidence of shoreline retreat -- it's all over the place," said Dr. Kearney, who also decried "out-of-control" coastal development with "people putting themselves in harm's way."

Some scientists trace the rising waters to melting of the polar ice caps caused by increasing average temperatures worldwide. They believe that gases such as carbon dioxide from cars and factories are trapping some heat from the sun that normally would escape the Earth's atmosphere.

Dr. Kearney and Stephen P. Leatherman, a College Park expert on sea-level rise and its impact on people, used historic maps, records and photographs, as well as satellite photos and their own measurements to document the rising waters and shoreline loss.

If predictions of dramatic sea-level rise by 2100 are borne out, the bay could experience "a thousand feet of shoreline retreat," obliterating some islands inhabited since Colonial times and threatening low-lying areas such as Kent Island, with a maximum elevation of 10 feet, and Smith Island, whose highest point, at 17 feet, is the landfill at the small community of Ewell, he said.

"It's time to do something about it" in the way of advance planning, said Dr. Kearney, an advocate of such measures as a joint Maryland/Virginia commission for formulating policies on future sea-level impacts.

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