Weekend Reads | How Climate Change Affects the Rise and Fall of Land

by Kevin Schofield

We hear a lot these days about sea level rise spurred by climate change: The seas are rising, and that poses existential risks for coastal areas. What we don't hear about — and what many people aren't even aware is a real thing — is the rise and fall of the land. But drops in land elevation, known as "subsidence," are very much real and affect large portions of the planet's land masses, including in the United States. This weekend's read is a report from scientists at Virginia Tech, United Nations University, and the U.S. Geological Survey on subsidence along the East Coast of the United States.

The largest source of changes in land elevation, both rises and falls, are glaciers. The weight of a massive glacier pushes down on the land it sits on and the underlying tectonic plates, lowering their elevation. But it also has the opposite effect on nearby land: Areas near a glacier will tend to rise. Think about it like a pillow: Push down in the middle, and the sides pop up, because all that stuff has to go somewhere. As glaciers subside, the reverse happens: The land once covered by ice slowly pops back up over thousands of years, and the nearby areas fall back down. Here in the Pacific Northwest, land that was once completely covered by glaciers, land elevations are rising over time; not as fast as sea level is rising, but a measurable amount. But along the East Coast, a substantial amount of subsidence is occurring: on average, 1 to 2 millimeters per year, and in a few places, substantially more.

To be clear, there is human-caused (or "anthropogenic") subsidence as well. Climate change has brought drought to many areas of the country, and significant draw-downs of groundwater have caused land to dry out and compact; the farmlands in central California have seen much of this over the past decade. In addition, the cumulative weight of dense urban areas also compresses the land.

The researchers looked at changes in land elevation in 172 counties along the East Coast and found that somewhere between 56 and 172 of them are seeing subsidence of more than 2 millimeters per year. That doesn't sound like much, but it accumulates: That's about an inch every 10 years, more than enough to cause problems for building foundations, railroad tracks, and roads. The report also shows our nation's "complacency toward maintenance" of critical infrastructure, with 14 coastal states having infrastructure in "poor" condition overall and at least 3,330 miles of interstate highway and 31,000 miles of primary and secondary roads exposed to subsidence. The American Society of Civil Engineers estimates that $786 billion is needed for its roads, $125 billion for bridges, and $45.2 billion for railways. This neglect makes this critical infrastructure more susceptible to failure due to land subsidence, putting lives at risk. The states with the highest exposure are Georgia and South Carolina in the South, along with Virginia, Maryland, Delaware, and southern New Jersey in the mid-Atlantic. According to the report, New York City's railways system, much of which is underground, is seeing more than 1.5 millimeters of subsidence per year, which compounds the risk from sea-level rise and "may cause the irreversible loss of this infrastructure in the future."

This is not on anyone's radar, and particularly not policymakers. It affects not just buildings and transportation, but also a wide swath of critical infrastructure: dams, levees, water distribution systems, schools and universities, hospitals, and airports. And the more the U.S. population continues to migrate toward and concentrate in coastal areas (the report measured subsidence within 60 miles of the ocean) the greater the threat becomes. "In absolute terms," the report says, "subsidence is a major threat worldwide and rapid urbanization of coastal zones leads to increased exposure of coastal communities and infrastructure."

So what's to be done? A starting point, the report argues, is better, more comprehensive, and regular monitoring. Even within towns and cities, there is plenty of variation in the amount of land subsidence, so there is a lot of data that must be collected to obtain a clear picture of what is happening to land elevations.

The scientists also argue that more work needs to be done to disentangle the subsidence occurring from natural causes, including glaciers, from the anthropogenic portion, so we can understand whether our society needs to change its practices to reduce further subsidence.

And, of course, we need to get serious about maintaining infrastructure to ensure it is resilient in the face of ongoing land elevation changes.

Slowly but surely: Exposure of communities and infrastructure to subsidence on the US east coast

Featured image via Stephen Wood/Shutterstock.com.