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Rising seas make Tampa Bay coastline more vulnerable

Since 1947, hour after hour, a simple tide gauge by the St. Petersburg Coast Guard Station has measured the water level of Tampa Bay.

These measurements are rudimentary, but they show more than the ebb and flow of the tides. Together with a worldwide network of tide gauges, our gauge is being used to study a key component of climate change: sea level rise. So what does our gauge tell us about sea level rise right here?

During the 63 years of the tide gauge record, the water level in St. Petersburg rose about an inch per decade.

An inch? Per decade?

That number will not alarm many, but an inch is worse than it seems. It is not how far up the water moves that matters, but rather how close to us the water gets.

Water does not merely creep up the beach inch by inch. Our beaches are dynamic, shifting piles of sand that are sensitive to changes in water level. In fact, the shoreline retreats up the beach a distance 50 to 100 times the change in sea level. In other words, a seemingly benign inch of sea level change leads to at least 50 inches of shoreline retreat. That's more than 4 feet, and it could be as much as 8.

A 2008 report by the National Ocean Economics Program finds that 59 percent of Florida's beaches are eroding. Certainly sea level rise is not the only factor contributing to the erosion, but it greatly exacerbates problems presented by storms and the natural shifting of barrier islands.

Considering sea level rise has occurred at the St. Petersburg tide gauge for decades, you may wonder why buildings are not falling into the Gulf of Mexico. A simple reason: We are already adapting to sea level rise. Sea walls are now ubiquitous fixtures of our landscape as we spend countless dollars hardening our shores against encroaching waters.

In addition, more than $1.1 billion was spent in the last 50 years to pump sand onto Florida's eroding beaches, and 7 percent of that was spent in Pinellas County. The majority of these funds were federal, and given federal budget realities, we cannot count on these dollars in the future. If we continue to deal with sea level change and erosion by simply acting defiantly, the burden of increasing cost will increasingly rest on the shoulders of Floridians.

Furthermore, residents of Tampa Bay are well aware of the region's exposure to hurricanes, and we are fortunate to have avoided the brunt of a major storm in recent decades. Eventually, though, we will have such an encounter, and the more sea level rises, and the more shorelines retreat, the more vulnerable we become.

Ultimately, sea levels will rise for the foreseeable future. Our current best guess is about 10 to 20 inches of rise by 2100, but scientists using new technologies are finding that glaciers and ice sheets are melting more rapidly than previously believed. Recent studies suggest 30 to 60 inches of sea level rise is possible. Thirty inches would flood more than $130 billion of Florida real estate and 99 percent of Florida's mangroves.

We will have to live with and adapt to these changes, but we have a critical role in the future of our coastlines. For example, should we continue to believe we can control the long-term shape and location of the ocean's boundary by repeatedly renourishing our beaches? Is it economically or even physically possible to constantly undo a large-scale natural process that will likely get much worse? It seems like trying to paint a house in the rain.

Decisions we make regarding where and what we build in the future need to reflect the current rate of sea level rise and the associated erosion of our coast. Our decisions also need to reflect the realities of climate change, including the possibility of a substantial increase in how fast sea level rise occurs.

We should remember that even small changes can have large impacts on our coastline. You don't have to believe all land in Florida will drown to take sea level rise seriously, and we don't have to wait until the situation is hopeless to make responsible choices.

Phil Thompson is a Ph.D. candidate in physical oceanography at the USF College of Marine Science. He uses tide gauges and satellite altimetry to study sea level and decadal changes in climate. His work is closely related to the research of Richard Alley and Steve Nerem, who will be speaking at the Eminent Scholars Lecture Series presented by the USF College of Marine Science Wednesday and Thursday.

Hear the experts

On Wednesday and Thursday, the University of South Florida College of Marine Science is hosting an eminent scholars lecture series on the twin topics of ice sheets and sea level rise and ocean acidification. The lectures will be held at the Karen A. Steidinger Auditorium at the Florida Fish and Wildlife Research Institute, 100 Eighth Ave. SE, St. Petersburg. Call (727) 553-1130 or go to for more information. All lectures are free and open to the public.

This chart, which looks like an electrocardiogram, shows Tampa Bay's monthly average water level as measured at the St. Petersburg Coast Guard Station. The variations reflect changes in sea level from month to month, though the mean seasonal cycle is removed for clarity. The dark line shows the increase in average sea level over time.

Rising seas make Tampa Bay coastline more vulnerable 03/01/10 [Last modified: Tuesday, November 8, 2011 1:32pm]
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