Olive Heffernan

Last week, I posted here on sea level rise and what’s in store for the 21st Century. Among scientists, that’s still a contentious issue, with current estimates ranging from about 18 cm to more than 200 cm by 2100 (see Figure 1 from a commentary by Stefan Rahmstorf; references are listed in full in the text).

I started to look into this issue in detail some months ago in preparation for a talk I was giving here at Nature. Given the knowledge that sea levels will rise this century, whether by a little or a lot, I also became curious about the extent to which coastal states are preparing for the impacts.

Regions will experience sea level rise differently, depending on factors such as whether the coastline is gaining or loosing sediment and the extent to which it is developed. The most vulnerable regions worldwide are large deltas such as the Netherlands and Bangladesh, countries with large low-lying well-developed coastal plains such as the US and China, and small island states such as Tuvala and Carteret Islands. And in terms of cities, Miami tops the list.

But in spite of its vulnerability, coastal development continues virtually unabated in Miami. In the first of two features Mark Schrope reports from Florida, a state that could be losing billions each year by 2050 if it continues business as usual. Florida, say experts, could serve as a case study for what happens if you don’t prepare for sea level rise. From Schrope’s feature:

“Right now Florida is showing almost no leadership on responding sensibly to storms and to rising sea level,” says Robert Young, a coastal geologist at Western Carolina University in Cullowhee, North Carolina. Orrin Pilkey of Duke University in North Carolina, a well-known proponent of greater constraints on coastal development, is even more forthright. “I call it an outlaw state,” he says. “Florida has been particularly irresponsible and it’s going to pay the price very soon.”

Worse than just ignoring the threat of sea level rise, Florida state has taken drastic action to ensure that waterside properties damaged in storms can be rebuilt in the same locations time and time again.

Planners and lawmakers in Florida would do well to learn from neighbouring Louisiana, one of a number of locations worldwide now adopting a ‘soft’ approach to self-defence. In the case of Louisiana, this means allowing the water to flood certain parts of the state during high storms in order to protect more valuable land elsewhere. Similar ‘ecological engineering’ approaches are being considered in the Netherlands, a nation that has traditionally hardened its coastline as a protective measure against an encroaching ocean.

But as Mason Inman reports in a second feature in the same issue, such hard defences are now under threat. Mason writes:

Ecological engineering approaches are often cheaper than fortifying coastlines with concrete walls or defending cities with ever-stronger levees, advocates say. And in the long run, they could be more effective. A similar philosophy is now being adopted in parts of the United States and Asia, and if its proponents are right, ecological engineering could become one of the main tools for adapting to rising seas. “With sea level rise, it’s not going to be possible for us to do engineering as usual,” says William Mitsch of The Ohio State University in Columbus. “It will be too much to try to fight head on, with hard defences to protect all the settled coasts.” Ecological approaches, he says, are “more about adapting to what’s happening, rather than fighting it”.

Ultimately, better projections are needed to determine the likely extent of future sea level rise. But in the absence of such information, incremental adaptation using soft approaches might be the best solution both from an environmental and a political point of view.