Long before the Pacific Ocean subsumes thousands of low-lying islands, waves will begin washing over them frequently enough to ruin groundwater supplies and damage crops and fragile infrastructure. A new report says this likely will render many coral atolls uninhabitable within decades—before 2030 in a worst case scenario and by 2065 in a more optimistic one.

“When you’re walking around the islands and you see kids there, you realize this isn’t something that’s next generation or the generation after that,” said Curt Storlazzi, a scientist with the U.S. Geological Survey and the study’s lead author. “If these scenarios play out, we’re talking about those kids’ generation.”

Some of these reef-lined islands are home to hundreds of thousands of people and American military sites.

In the study, commissioned by the Defense Department and published Wednesday in the journal Science Advances, the scientists combined climate projections with weather and wave modeling to look at the impacts of rising seas on an island in Kwajalein Atoll. Kwajalein is part of the Marshall Islands and home to the Ronald Reagan Ballistic Missile Defense Test Site, which has been used to test U.S. defenses against a nuclear attack.

The Air Force spent nearly $1 billion in recent years building a facility there to track space debris. But a report by the Associated Press found in 2016 that the Defense Department and contractor Lockheed Martin paid little attention to projections for rising seas when planning and constructing the site, which is intended to have a 25-year life span.

John Conger, who was Assistant Secretary of Defense for Energy, Installations and Environment under President Obama and is now director of the Center for Climate and Security, said the project illustrates how much money the Pentagon could waste if it fails to adequately plan for rising seas and climate change.

“You’ve got to think this through,” he said. “A lot of people have asked me in the past about how much the department is going to invest in dealing with climate change, and I think it’s the wrong question to ask. I think climate change is an important factor to study to save money.”  

Lessons from a 2008 Storm Surge

As the planet warms, rising seas will pose a risk to hundreds of the United States’ coastal military sites, with more than 200 already reporting effects from storm surges. The new study suggests that without global efforts to rapidly cut emissions or expensive mitigation projects, the facilities on low-lying islands may have even shorter lifespans than sea level rise projections would indicate.

Storlazzi began studying the issue after a winter storm hundreds of miles away sent water surging over the Marshall Islands in 2008.

“It had destroyed the groundwater so much, they had to fill up tankers and take freshwater out to a lot of these atoll islands,” he said.

Storlazzi and his colleagues found that with about 16 inches of sea level rise, such waves would wash saltwater over Roi-Namur island on Kwajalein Atoll about once a year. When that starts happening annually, the island’s aquifer will be unable to recover, the authors said.

“Even if we don’t worry about the groundwater issue, when seawater floods through cars and buildings and infrastructure every year, that’s going to have an impact,” Storlazzi said. While the study was specific to Kwajalein’s topography, the effects of sea level rise will likely be similar on thousands of other atolls and reef-lined islands across the tropics.

Temporary Adaptation — at a Cost

At the Defense Department’s request, the authors considered three scenarios for rising seas: one in which emissions stabilize mid-century and two in which they continue to rise. In the most optimistic scenario, annual flooding would still likely begin between 2055 and 2065.

The island can be protected, at least for a time, with measures like building seawalls and shipping in water. But the costs will continue to rise, Conger said.

“The nearest-term impact is going to be on drinking water,” he said. “How expensive is it going to be to get drinking water out there?”

Most of the atolls, of course, do not host military bases, and governments of these island nations may not have the money to pay for coastal protections, leaving residents exposed.

Military Studies Show Bases Face Climate Risks

The Pentagon has been studying the impact of climate change on its facilities and national security for more than a decade. In 2014, an Army Corps of Engineers study determined that about 1.5 feet of sea level rise could bring a “tipping point” for the Navy’s largest base, in Norfolk, Virginia, where the risk of damage to infrastructure would increase dramatically. That level is expected to be reached in the next few decades.

In January, the Defense Department published the results of a survey of nearly 1,700 military installations that found about half reported experiencing at least one weather-related effect associated with climate change, such as wildfires, drought and flooding.  Last year, the Government Accountability Office said the military was failing to adequately plan for climate change at overseas facilities.

Now, the military’s work may be caught up in the Trump administration’s hostility toward action on climate change. The Defense Department’s response published with the GAO report, for example, said that blaming infrastructure damage from weather on climate change was “speculative at best and misleading.” Two key strategy documents issued by the Trump administration this year—the National Defense Strategy and National Security Strategy—omitted references to climate change that had been included in earlier versions.

But where the administration may be pushing one way, Congress has begun to push in the other. Last year, lawmakers included language in an annual defense budget bill that declared climate change to be a national security threat and required the Pentagon to issue a report to Congress this year assessing vulnerabilities to climate change over the next 20 years, including a list of the 10 most at-risk facilities in each service.