A new Pentagon-funded study published in Science Advances last week claims that rising sea-levels will render “thousands” of tropical islands in the Indian and Pacific Oceans uninhabitable by the middle of the century.

The study focused on the Marshall Islands in the Pacific Ocean and specifically Roi-Namur Island, where the US runs a military base that is home to over 1,200 personnel and civilians. According to the study, a combination of large waves, rising sea levels, and the collapse of the coral reefs around the islands threaten to completely inundate many of the low-lying islands between 2040 and 2065. Roi-Namur, which lies only 6 feet above sea level will probably avoid being completely submerged this century, but is still at risk of becoming uninhabitable.

In the immediate future, the main threat to Roi-Namur and the other islands are that large waves can carry their water across the island and deposit salt into the water table and make the fresh water undrinkable.

The study’s lead author Curt Storlazzi, a researcher with the US Geological Survey, told the Washington Post that these types of “overwash” events happen naturally occur once every few decades and this gives communities and the environment time to recover. Yet as the sea level continues to rise the authors of the study predict these types of events will happen more frequently. If a wave washed over the island two years in a row, for example, the salt deposits in the island’s water would render it uninhabitable.

“This information, when applied broadly to all islands, will be critical to political leaders globally because it will enable them to identify which island nations and human populations will be displaced and when this displacement is likely to occur,” reads a Department of Defense statement on the study. “If these impacts are not addressed or adequately planned for, as it becomes necessary to abandon or relocate island nations, significant geopolitical issues could arise.”

In addition to the immediate threat to the tens of thousands of people who call these Pacific islands home, there will also be collateral damages in unlikely sectors, such as space. The US military is in the home stretch of constructing the so-called ‘Space Fence,’ a $1 billion radar system on Roi-Namur that will be responsible for tracking the tens of thousands of pieces of space debris currently in orbit. Rising sea levels place the instillation in danger of being knocked out by big waves or rising sea levels.

The ocean levels have risen by about six centimeters globally since 2000 and continue to rise at about a rate of 3.4 millimeters annually although this rate can be expected to accelerate in the coming years. A big unknown in predictions about how climate change will affect global ocean levels in the future is the fate of Antarctica. Over the past few years, climate scientists have “ watched in horror” as the West Antarctica ice sheet has begun to collapse.

If—or rather, when_—_the West Antarctic ice sheet completely collapses, this could lead to ocean levels rising by as much as 12 feet. More than enough to submerge US coastal cities like Miami, to say nothing of the low lying Marshall Islands, which will each become their own Atlantis. The good news, if you will, is that this process will likely take 200 years or more to occur. Yet according to a 2013 report by the International Panel on Climate Change, oceans could rise between 4 inches and three feet by 2100, although many climate scientists feel this is a conservative estimate.