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.
This means that as the surface of the water is warmed by climate change, sound will begin moving more sharply downward toward cooler layers of water. This will make it harder for sonar operators listening for submarines at a distance to hear noises generated by their targets.
According to Dr. Gilli, who has worked at ETH Zurich and is taking up a new research position at the Hertie School in Berlin, this effect could have important strategic implications. He said countries like Russia and China could take advantage of these environmental shifts to deploy submarines in parts of the oceans where the changes are more pronounced, such as the North Atlantic.
Dr. Gilli noted that other methods of detecting submarines, like tracking the tiny disturbances in Earth’s magnetic field that occur when the submarines move through the water, are effective only at shorter distances.
“If it becomes even more difficult to detect them,” he said, “then the result is that things become harder for navies that are on the defensive.”
There could be consequences in terms of nuclear deterrence.
The United States, Russia, China and other nuclear-armed states base their defenses on the idea that ballistic missile submarines are hard to find and destroy. If climate change makes it even easier for them to hide, then the threat they represent, and thus their deterrence value, may be seen as more credible.
But some experts caution against overstating the effects caused by climate change. Tom Stefanick, a nonresident fellow at the Brookings Institution, notes that submarine operators must grapple with so many other environmental factors, from shipping noises to crackling Arctic ice, that it is not practical to focus only on climate change when making strategic predictions.
“The amount of variability is so great that a long-term trend of the sort they are talking about would be washed out,” Dr. Stefanick said.
The most important finding of the study may simply be a confirmation that submarine fleets will be forced to grapple with greater uncertainty in the future as climate change accelerates.
Dr. Gilli and his colleagues found that ocean changes would vary substantially in different areas and were more pronounced at northern latitudes. In the shallows of the Sea of Japan, detection of North Korean submarines could actually become easier.
“This creates an unpredictability that will now be something that commanders will have to contend with,” said Bryan Clark, a senior fellow at the Hudson Institute, who added that changing currents and weather will also present challenges. “You will have to do much more frequent measurements to make sure your models are up-to-date.”
The U.S. Navy has gradually become more attuned to the risks that climate change poses to its operations. But since January, the Trump administration has been rolling back efforts to address climate change throughout the government. The Pentagon announced in March that it would begin canceling programs like the Navy’s Climate Action 2030 plan, which sought to reduce emissions and bolster climate resilience.
But scientists working for NATO are warning that climate change will cause difficulties to accelerate. They point out that coastal infrastructure is put at risk by sea level rise and erosion, and say that vessels operating in saltier and more acidic waters will need more frequent maintenance. They even note that jellyfish swarms, which are becoming increasingly common, have caused warship engines to overheat by clogging propulsion and cooling systems.
Sandro Carniel, a researcher with the Italian Institute of Polar Sciences who has worked with the NATO Center for Maritime Research and Experimentation, says that modeling the way climate change is altering ocean conditions can offer militaries a unique opportunity to adapt their fleets.
“I am not telling you to throw away your submarine or your sonar,” said Dr. Carniel, who worked on an earlier version of Dr. Gilli’s paper. “But if you do not manage this problem, then it will manage you.”
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