Luntz writes that scientists expect climate change to spur global sea level to rise 7 inches to 23 inches this century —  and up to 3 feet in the worst-case scenario. The corps has had a planning policy for rising sea levels since 1986, but the instructions were less than a page long, buried in a 1,000-page document and largely ignored. “If you think about the public opinion at the time in the country, nobody was really paying attention to this,” White said. “I don’t think planners were explicitly saying, ‘We’re not going to do this.’ I think it was more, ‘This is kind of an oddball thing, and our stakeholders don’t like it.’”

The new, 44-page stand-alone document, released in July, sends a clear signal that the corps is serious about planning for sea-level rise, White and Knuuti said. White said the policy was sparked by the aftermath of Hurricane Katrina, when crucial flood protections failed in New Orleans.

A 2006 report by the Interagency Performance Evaluation Task Force blasted the Army Corps for failing to consider changing environmental conditions, including sea-level rise, in the lead-up to the catastrophe.

The new corps guidance directs staff to consider three scenarios.

At a minimum, they must estimate how the historic rate of rising sea levels would affect a project. Then they must evaluate accelerated rise rates that mirror those projected by the Intergovernmental Panel on Climate Change. Finally, planners must consider an even higher rate meant to address criticism that the IPCC underestimated how quickly glaciers are melting.

Knuuti said the policy will challenge the Army Corps’ standard procedure, which focuses heavily on assessing the economic viability of projects.

“When we look at multi-scenario approaches, that takes us out of our standard way of doing business,” Knuuti said. “It makes it a little harder to assess the economics of the project. It just means we need to think in a nontraditional manner.”

The Army Corps’ coastal engineering projects often make new development possible in shoreline towns and cities, which then turn to the agency to protect them from flooding. Some projects, however, especially those in low-lying regions, may look less appealing when considerations for sea-level rise are built in, EPA’s Titus said. “This isn’t a fundamental decision by the corps to stop holding back the sea, but it is a signal that the corps isn’t going to simply pretend that lands are not vulnerable when they make these decisions,” he said. “That in itself should be at least a bit of a warning to anyone who assumes that the government will always protect them.”

Luntz notes that the guidance does not apply to the corps’ regulatory program, which oversees permits for state and local activities like dredging, bulkhead construction and beach fill. White said the corps is planning “in the fairly near future” to work with EPA, the Fish and Wildlife Service and other agencies that share water oversight to develop a sea-level policy for that program.

White said, however, that current policy may prompt coastal regions to take a closer look at their planning guidelines. “State or local regional planning groups might say, ‘Oh, the corps got a new policy on this; let’s review our own,’” White said. “It could spur some conversations about what kind of considerations they have to take.”

Jeffrey DeBlieu, climate adaptation projects adviser for the Nature Conservancy, said the Army Corps’ initiative is encouraging. He cautioned, though, that important decisions will be made on a project-by-project basis, when the agency determines which of the three sea-level scenarios to plan for. “It looks like it’s a pretty solid approach, and it’s really great to see them moving in this direction,” DeBlieu said. “But how it plays out in future decision-making, that’s where the rubber meets the road, and we’ll just have to wait and see.”