Sea Level Rise is real, predictions still to come
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06/05/12 Janelle Irwin
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Planners in coastal localities may have to consider sea level in building.


photo by Janelle Irwin

New technology is making it easier for scientists to study changes in sea levels. During a UNESCO Ihe international water institute conference on May 24th, experts talked about what coastal regions might expect in the coming decades. Gary Mitchum, the Associate Dean of USF’s College of Marine Science, celebrates the huge influx of data over the past several years. But he said it’ll still take ten years before there will be enough to make accurate projections.

“Right now, we can give you our best guess but it has a substantial error bar – an uncertainty associated with it. So what I tell them is, if you have to make a decision about something but you don’t need to decide for ten more years, then wait. If you really need to know something that’s going to last 80 years, should I build it here or not? In that case, we’ll give you our best guess.”

One thing he is sure of is that it is rising. The type of sea level rise Mitchum studies doesn’t account for substantial changes.

“But for us, could be big because a meter or two meters of sea level change – there are a lot of people living within that distance of the sea surface right now.”

Mitchum uses three tools to measure sea levels. They are used together as a sort of check and balance system. Argo floats are sunk into the water and then resurfaced to measure density. Then there’s GRACE – the Gravity Recovery And Climate Experiment that can actually weigh ice sheets at the poles. Those two systems are combined and if the results match the third measure –altimeters – they are considered accurate. Altimeters use satellites to gather information.

“It actually puts out a radar pulse, bounces off of the sea surface back to the satellite and by measuring the travel time, they can determine the height of the sea surface.”

USF researcher Jochen Eckart works on the Resilient Tampa Bay program. That group considers various risk factors associated with Florida’s ecology.

“We have urban flooding. You know, we have these heavy tropical winds and not always the drainage system functioning as well as it should. So we have certain hot spots where we have, once and a while, a flooding that’s caused damage. Then, of course, we’re in a region where we face hurricanes. Tampa Bay wasn’t hit by a big hurricane for 90 years, but doesn’t mean it can’t happen in the future.”

Eckart said continued sea level rise could make those risk factors worse.

“It’s a threat multiplier. So, all the threats we already have with hurricanes, the hoverability. Everything will increase when the sea level will rise and this is what is predicted. There are projects that there is already sort of a measurable sea level rise over the last decades.”

Both Eckart and Mitchum attribute at least some sea level rise to climate change. Eckart and others from Resilient Tampa Bay work to bring groups together to mitigate sea level rise.

“There are a lot of ideas around what’s at risk in Tampa Bay. So, there’s a lot of rumors around. What’s missing is this one simple way where you can tell somebody in 15 minutes, look, this is the risk we face in Tampa Bay. This is really where we are and a good track with resiliency, here’s where the gaps are.”

Mitchum said there isn’t enough data yet to debunk claims that sea level rise cyclical.

Mitchum said there are two main causes of sea level rise; water getting warmer and ice on land melting. As he and others continue to monitor sea level changes, the range of predictions is expected to narrow. Right now Mitchum’s lowest estimate is a 20 centimeter change in height over 100 years. The most drastic model puts that figure at two meters.

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