Global Warming Means

Rising Tides for South Florida

By Rosalie E. Leposky

Earlier this month, delegates from 160 nations met in Buenos Aires, Argentina, to debate details of a global-warming treaty sponsored by the United Nations.

If global warming is a reality, what will it mean to life in South Florida? Fewer winter cold fronts, perhaps, but first and foremost an increase in sea level as alpine glaciers and arctic icecaps melt, releasing their stored moisture into the oceans.

"The evidence that we are entering a stage of global warming is compelling but not convincing," says oceanographer Dennis A. Mayer, a senior scientist with the National Oceanic and Atmospheric Administration (NOAA) on Virginia Key. "Climate as manifested by average air and sea surface temperatures has a very long time scale, with fluctuations from decades to a century or longer. We could be at the rising part of a cycle that could take 50 years to peak. Evidence still is being accumulated."

Some Evidence

Mean high tides around the southern tip of Florida’s coast from Naples to Miami Beach have been rising about a foot every 100 years for the last 5,000 years, but tidal records in Key West show an increase of about a foot in just the last 70 years.

"We have better records for Key West than other South Florida communities. Some of Key West’s records date back to the 1860s," says Dr. Harold R. Wanless, chairman of the University of Miami’s department of geological sciences.

If this trend continues, higher tides and increased flooding associated with dramatic events such as hurricanes will bring costly environmental and economic changes. A Category Two hurricane or even a bad storm that pounds a beach area for a day can cause major erosion.

Insurance and Drinking Water

"High storm tides will more easily wash over the lowest areas in the Keys and on barrier islands, and regularly flood low-lying coastal areas. How long can we continue to afford to restore beaches?" Wanless wonders.

"Flood-zone maps will have to be revised, and that higher flood risk translates into higher rates for flood insurance," adds Dr. Terry A. Nelsen, a NOAA marine geologist and senior research oceanographer.

"The South Florida Water Management District says that an 18-inch rise in sea level will make their whole gravity-based Everglades and coastal drainage system unworkable," notes Wanless. "Most important, higher regular tides means more salt-water intrusion into the Biscayne and Florida aquifers, the source of South Florida’s fresh drinking water."

Migrating Mangroves

Higher regular tides in the red-mangrove zone are pushing the red mangroves to try to migrate to higher land, but much of that higher land now is blocked by seawalls and developments. Wanless notes that only a third of the 80,000 acres of mangrove swamps destroyed by Hurricane Andrew in 1992 will grow back as mangrove swamps. The rest are being replaced by ponds and lagoons.

Meanwhile, coral formations in Biscayne and Florida bays are experiencing stress from changes in water quality associated with the increasing depth of the water, which leads to stronger wave agitation and tidal currents that bring higher levels of nutrients and organic materials.

Ampersand Communications

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