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UA climate research: Big stretch of US coast at risk of rising seas

February 23, 2011


If global temperatures continue to rise and polar ice continues to melt, 9 percent of the land in our coastal cities and towns will be beneath sea level by the end of the century, University of Arizona researchers say.

Climate researchers Jeremy Weiss and Jonathan Overpeck, along with Ben Strauss of Climate Central in Princeton, N.J., mapped the U.S. coastline, using elevations provided by the U.S. Geological Survey. They applied the most recent predictions of a sea level rise of 1 meter (3.28 feet) by 2100 to produce a map that predicts big trouble for 20 cities with more than 300,000 people and for 160 smaller municipalities.

Weiss is a senior researcher in geosciences. Overpeck is a professor of geosciences and atmospheric sciences and co-director of the UA’s Institute of the Environment.

The report was published last week in Climatic Change Letters.

The biggest impact will be felt in low-lying, heavily populated places such as New Orleans, Miami Beach and Virginia Beach, the report says.

Subsequent centuries will bring even higher sea levels that could completely submerge some large coastal cities, the researchers say.

It’s not news in New Orleans, said geographer Richard Campanella of Tulane University. Half its urban area is already below sea level.

It was above sea level in the late 19th century, he said, but levees built to protect New Orleans from seasonal floods on the Mississippi River starved the delta of fresh water and sediment. Municipal drainage projects subsequently caused the soils to compact. The city sank, and continues to do so, Campanella said.

Weiss said his study did not consider the impact of protective measures such as sea walls and levees, which are in place in New Orleans and other areas on the map.

Campanella said those protections will fail if sea levels rise as predicted.

It is tough to protect places like Miami Beach, said Robert Deyle, a professor of urban and regional planning at Florida State University.

You could build a huge sea wall around Miami Beach, but infiltration of its shallow aquifer would just fill it like a bathtub, he said.

Deyle said many areas of Florida will face adverse effects from sea-level rise long before the end of the century.

Infiltration and increased property damage from storm surges will be the first signs, he said. A report he prepared with other Florida State researchers says a storm with a severity that could be expected every 100 years would have the force of a 500-year event with a meter’s rise in sea level.

“The message from our work,” said Weiss, “is that one of the most popular landscapes we want to live in or recreate on – the coast – is looking squarely at major impacts from rising sea level in the next century.”

The change will be incremental, said Weiss.

Those polar ice sheets in Greenland and Antarctica melt slowly, like a block of ice in the sun, he said. If nothing is done to reduce greenhouse-gas emissions and rising temperatures, they will continue to melt over centuries, placing 36 percent of our urbanized coastline beneath sea level, the report says.

“Temperatures by 2100 may be warm enough to commit Earth to at least 4-6 m(eters) of global SLR (sea level rise) over following centuries as the polar ice sheets adjust to the comparatively rapid and largely irreversible global warming that occurs this century,” the report says.

“In terms of sea-level projections, we’re looking squarely at one meter of rise by 2100 with the continuing of current rates of greenhouse gases,” said Weiss.

With that rise only 90 years away, he said, it could affect people born today.

Deyle said Florida governments are beginning to plan for rising sea levels, but he still hears remarks such as “I’ll be dead by then.”

“All the alternatives are really expensive and politically fatal,” Deyle said.

Barrier islands and low-lying beach towns are not the only targets of sea-level rise, the report says.

Cities with bay and river connections, such as Philadelphia, Portland, Ore., and Washington, D.C., will also be affected.

The Gulf Coast states and the Southern coast will be hardest hit, the study says, but coastal land everywhere will be affected.

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