Climate change is no laughing matter. Uncontrolled, human-caused climate change is a real threat to the United States economy, hundreds of millions of Americans, and their local communities. The increasingly extreme weather of the past few years is a sign of things to come: rising temperatures, changing rainfall patterns, increasing storm and drought frequency and intensity, changing vegetation, and rapidly disappearing Arctic ice. There are plenty of remaining uncertainties -- such as the speed of the changes, their extent and severity, the costs of suffering impacts versus the costs of adapting to or preventing them -- and the scientific community continues to work hard to understand and reduce these uncertainties. But one of the most certain and devastating consequences for the United States is going to be the very climate impact that Romney chose to mock: rising seas.
Sea levels are rising for two reasons: thermal expansion and an increase in the volume of the ocean. As the planet warms, so do the oceans, and warmer water takes up more space than colder water. As ice in glaciers and the ice caps on Antarctica and Greenland melt, the volume of the oceans grows. And we already see rising sea levels. Between 1993 and the present, sea levels have been increasing an average of over 3 mm per year -- more than 50 percent faster than over the past century. Indeed, sea levels are actually rising at the upper range of model projections, and there is growing concern that scientists have conservatively underestimated the speed at which some of the massive ice volumes in Greenland may deteriorate and melt. There is so much ice on Greenland alone, that were it to melt into the oceans, sea levels would rise nearly 24 feet.
A global increase in sea level of a meter (more than three feet) by the year 2100 is now "widely accepted as a serious possibility" and even the U.S. Army Corps of Engineers recommends planning for as much as 1.5 meters (nearly five feet).
What is even clearer are the risks to our populations and economies posed by this threat. The United States has a vast and vulnerable coastline. More than half the nation's population lives in coastal counties. Nearly four million people already live within three feet of today's high-tide level, with hundreds of billions of dollars of infrastructure at risk. Residential structures in today's 100‐year floodplain of just New York City and Nassau, Suffolk, and Westchester counties already have a total estimated value of over $125 billion. New York's Sea Level Rise Task Force identified a wide range of growing threats associated with sea-level rise, including storm surges, inundation and flooding, rising water tables, salt water intrusion to groundwater, and coastal erosion. More
