The Chesapeake Bay region—which includes major coastal cities such as Washington, D.C., and Baltimore—could see worse flooding and storm damage from rising sea levels than even neighboring areas, according to a group of geoscientists.
Last week, the scientists published a report in GSA Today that explains that the region is vulnerable to a slow geological change "subsidence" that has occurred over several millennia.
More than 20,000 years ago, a massive sheet of ice stretched from the Arctic down the east coast of North America, ending roughly where Long Island, New York, is today. This ice sheet was so large and heavy that it placed enormous pressure on the Earth's crust, which in turn pushed molten rock in the mantle southward toward the Chesapeake Bay—a bit like squeezing toothpaste out of a tube.
Over time, the ice sheet slowly melted, releasing its pressure on the crust, and the displaced mantle rock that had been pushed up in the Chesapeake Bay began sinking back down. That means that the bay is sinking into the ocean at a rate of 4.2 millimeters per year—twice the rate of the global average.
That may not sound like much, and it will occur so slowly that it will be invisible to the human eye. It will also affect some areas more than others. But it already puts the Washington, D.C., area—along with all of its monuments and military facilities—at greater risk of damage from flooding, hurricanes and storm surges.
"This is nothing we have control over; there is no policy that can reverse this," said Ben Dejong, lead author of the study, though he added that the phenomenon is worsening sea level increases that are widely believed by scientists to be caused by controllable human activity.
The Intergovernmental Panel on Climate Change estimates that sea levels will rise roughly a foot or more by the end of the century. Even though the seas will inevitably continue their rise, there are ways to plan for the change.
The White house released a report in May calling climate change a "national security issue." Climate change is considered to be a contributing factor to climbing sea levels.
The Department of Defense released a report in 2014 that outlined the ways the military will have to adapt to climate change, noting that "[d]ecisions on where and how to locate future infrastructure will become increasingly reliant on robust risk management processes that account for dynamic factors associated with climate change."
In the Chesapeake Bay region, some military bases have already made some changes to accommodate higher water levels. A naval base in Norfolk, Virginia, has built its docks higher as water levels have climbed, and the low-lying land where the base is built is vulnerable to flooding, according to a National Public Radio story.
The effects of rising sea levels in storm surges and in severe storms such as hurricanes are among the few long-term environmental trends that reinsurers and other companies can confidently forecast. And mere centimeters make a major difference, especially over time.
"If Hurricane Sandy occurred in 2022 instead of 2012, the surge from Sandy would be on sea levels that are 3 centimeters higher in New York Harbor," said Mark Bove, senior research scientist and meteorologist for Munich Reinsurance America. "Now 3 centimeters doesn't sound like a lot, but that could be enough to send the surge inland a few hundred feet more and flood a few more basements and buildings. And the further you go out in time, the greater the effects of storm surges will be, and that is due to the fact that sea levels will be higher."
That risk does matter in dollar terms. Munich Re's own analysis estimates that Hurricane Sandy caused about $68 billion in total damages in the United States, Canada and several countries in the Caribbean. Only about $29 billion of those losses were insured.