Submarines are among the most advanced and deadly weapons systems in the world. Armed with torpedoes, cruise missiles and sometimes intercontinental ballistic missiles, they’re capable of operating deep below the surface for months at a time and are notoriously hard to detect.

Now, their ability to hide in the vast oceans may be getting a boost from an unlikely source: climate change.

The waters where many submarines lurk have been quickly warming, as humans pump out greenhouse gasses and oceans absorb the excess heat that gets trapped in the atmosphere. And that warming, according to a recent paper produced by the NATO Defense College in Rome, can have a powerful effect on how sound, the primary means of detecting submarines, behaves underwater.

It could make large areas of the oceans impenetrable to submarine hunters.

“We observed, in most areas that we looked at, a reduction in the range of detection,” said Mauro Gilli, a researcher who studies military technology. His team modeled the way sound waves moved through the depths from 1970 to 1999. And they compared it with the way current climate modeling predicts they will move between 2070 and 2099. There were significant differences.

The researchers found that in the North Atlantic, where Russian submarines play cat and mouse with NATO forces, the distances at which they can be heard will shrink significantly. This could be by almost half in the Bay of Biscay, off the coasts of France and Spain. There were similar dynamics in play in the western Pacific, where Chinese and American submarines operate and where detection ranges could shrink by up to 20 percent.

The underlying science has been well understood since before World War II, when scientists discovered that sound, which travels faster through warmer water, tends to bend toward cooler layers, where it moves more slowly.