From Al Gore to the leadership of groups like the Union of Concerned Scientists, environmentalists long have warned that global disaster is certain unless we do something about rising sea levels. The “something” that most on the left want is to remake our energy economy and increase government control over energy use in order to cut down on human emissions of greenhouse gases that cause the thermal expansion of ocean water and the melting of polar ice sheets.
A look at the facts reveals a less alarming, although still disconcerting, environmental picture. When it comes to combating and adapting to rising sea levels, many of the factors most within our control are not directly associated with the climate.
The environmentalists deserve some credit. It is beyond dispute that greenhouse gas emissions are the most important factor behind the global rise in sea levels. Releasing carbon dioxide and other greenhouse gases into the atmosphere, largely from burning fossil fuels, traps heat from the sun. Over the past two decades, global sea levels have been rising at a rate of slightly more than 0.11 inches per year.
But projections about the future extent of the trend remain too imprecise to be of practical use to policy-makers. The United Nations’ Intergovernmental Panel on Climate Change predicts that the “most likely” case is that global sea levels will rise between one and four feet over the next century. A continuation of the trend of the last 20 years (roughly twice the average rate most scientists believe seas rose over the 20th century) would result in total sea-level rise near the low end of the IPCC projections.
Although many models indicate the rate will accelerate, whether it does, and by how much, will make an enormous difference. A one-foot rise would be reasonably easy to deal with in many places, while four feet could be catastrophic. And complex climate models have a dismal record of predicting the future.
It’s also important to note that greenhouse gas emissions are not the only factor in climate change, and that climate change is not the only cause of rising sea levels. In North America, relative sea levels are changing not only because of rising waters, but also because of sinking landmass. The East Coast has been slowing sinking for thousands of years. The intersection of these two phenomena, rising seas and sinking landmass, could make sea-level rise doubly destructive in certain parts of the country.
For instance, along the Gulf Coast of Louisiana, sea-level rise appears to be happening at nearly a dozen times the global rate: nearly an inch a year. The reasons are complicated, but relate to tectonic shifts in the ocean floor. The consequences could be disastrous. Much of southern Louisiana may be inundated in the next century, and parts of Texas may not be that far behind. And, if the projections are right, controlling greenhouse gas emissions would do almost nothing to change things.
Development has made an already severe natural problem worse. A century-long project to control the Mississippi-Missouri River system and prevent flooding has reduced the amount of silt the river carries. This results in “silt starvation” that is slowly eating away at the land in the Mississippi Delta.
Also contributing to this kind of erosion have been the heavily subsidized National Flood Insurance Program and local economic incentives to build in river valleys and along the coasts. Other causes are more bizarre. The nutria or “river rat,” a South American critter that fur farmers brought to the United States in the 1940s, has no natural predators here and feasts on the plant life of coastal marshes. Along the Chesapeake Bay and other areas, river rats eat so many plants that the land is left bare and gets washed away.
For the regions most likely to face dramatic impacts from rising sea levels in the near future, no amount of emissions control will make a major difference. In fact, for some, the only solution may be to relocate people and property away from the coast.
At a minimum, in our most densely populated hurricane-prone areas, like the New York/New Jersey and Miami metropolitan areas, large investments in “structural mitigation,” seawalls and the like, is almost certainly going to be necessary to protect lives and property. Spending several billion dollars to protect Manhattan from rising seas and hurricane-driven storm surges will almost certainly offer a very good return on investment, even if 21st-century weather patterns aren’t significantly different from those of the last century. A vigorous nutria control and eradication effort is also in order, as are local zoning standards that take potential sea-level rise into account.