Republicans, eschewing climate change, converge in risk-prone Tampa

Many Republicans poised to stream into Florida for their nominating convention next week have doubts about climate change, if polls are right. Yet scientists say the GOP's swashbuckling event is happening within sight of climate impacts.

Tampa is Florida's second-largest metropolis, with dense clusters of homes, hotels and an arena hugging the curved shoreline of massive Tampa Bay, a two-headed body of water that merges with the Gulf of Mexico.

That makes the region vulnerable to rising ocean water, farther-reaching storm surges and, perhaps, stronger hurricanes, experts say. From the landward side, Tampa could face diminishing water supplies, rising temperatures and expensive decisions about how to protect itself.

"It's a big problem," Asbury Sallenger, a scientist who heads the U.S. Geological Survey's program on coastal hazards, said of rising seas in the Tampa area. "It's a lot of [urban] development with low-lying land."

Submerged under the Gulf waters near Tampa is a huge platform of natural limestone that yawns 300 miles out to sea, toward Texas. It's shallow, too, representing a massive cleft of Florida that was lost to the sea in ancient times.

One characteristic of this continental shelf is stability. That provides pluses and minuses for the city's shoreline. It's not sinking, in contrast to stretches of the U.S. East Coast where subsidence is exacerbating sea-level rise. The area's firm foundation, combined with a lack of ocean currents that accelerate the rise of coastal water depth, means that sea levels around Tampa are climbing at about 2 millimeters a year, roughly 1 inch every decade. That is about 1 millimeter less annually than the global average.

But the shelf also poses hazards. It is a shallow ramp that can send large surges of ocean water into Tampa Bay and, during rare hurricane scenarios, push piles of storm-driven water more than 25 feet high onto the streets of downtown Tampa.

"There are a few places around the country that most of us who studied the problem are just absolutely terrified about," Kerry Emanuel, an atmospheric scientist with the Massachusetts Institute of Technology, said of hurricanes. "One of them is the [Florida] Keys, just because you can't get people out of there. The other is Tampa. Tampa is much, much more vulnerable to huge storm surges than Miami is."

Protect Tampa; retreat unlikely

The main reason for that is the shallowness of the continental shelf and of Tampa Bay, which in undredged areas is about 11 feet deep.

As a result, some are proposing large investments in protective measures to avoid future flooding in the area of Tampa where the Republican convention is being held. Its location at the Tampa Bay Times Forum, between Channelside Drive and Old Water Street, is on a shore of interlaced channels navigated by freighters steaming in from the bay.

Maps depicting a 1-meter rise in the ocean, a scenario that many scientists expect to occur by the end of this century, show that significant areas of Tampa rimming the shoreline could be submerged.

"As sea levels continue to rise, much of the currently developed, increasingly populated, area can be expected to be flooded," says a report by the Tampa Bay Regional Planning Council. "Planners must begin to decide which land areas in their counties and municipalities will be protected, if any, against sea level rise and what the cost of holding back the sea will be."

Some computer models developed by sea-level rise experts predict that the oceans will begin climbing at an accelerating rate in 20 or 30 years, as land-based ice sheets melt more rapidly. If that happens, seawater could rise at a rate about three times faster than it is now, or by about 9 millimeters a year.

The next New Orleans?

Some scientists are more cautious when interpreting the models. Thomas Cronin, a senior scientist at the U.S. Geological Survey who has studied Tampa's rising oceans, says there is a lot of uncertainty about how fast the rise will occur. But he says an acceleration is likely.

"I hate to cop out, but it depends on one's time perspective," Cronin said. "All lines of evidence from past rates of sea level rise and from our current understanding of the ocean and ice system today suggest that we're going to see a higher rate of sea level rise in the next century than we have in the last century."

Tampa has been lucky so far. It has not sustained a direct hurricane strike since 1946, when a Category 1 storm -- the weakest kind of hurricane -- rumbled up the bay, according to a report on Weather Underground by Jeff Masters, the site's director of meteorology. Only one major hurricane has made landfall at Tampa in the past 90 years, a Category 3 that struck in 1921, when the population of the metropolis was 160,000, almost 20 times smaller than it is now.

There is an additional climate hazard to the Tampa region, apart from its dense population, lack of hurricane experience and shallow bathometry. It's called the Kelvin wave.

These are fast-moving waves that speed north along coastlines, often after they have traversed the open ocean guided by the equator. They can be big and, when combining with a hurricane, can increase the size of a storm surge. The Kelvin wave is only found on west-facing coastlines, so it is a risk that Miami and other East Coast cities won't see.

Together, the risks faced by Tampa could make it "the next New Orleans" after the Louisiana city's devastating strike by Hurricane Katrina, said Emanuel of MIT.

"With any luck, it won't happen within our lifetime. But sooner or later, Tampa is going to get really badly affected," he said. "Climate change can make that worse."

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