Climate change may make it harder to spot submarines
A submarine must remain undetected, eluding hydrophones towed by ships, dropped from planes and strung along the seabed. Just how quiet it needs to be depends on the surrounding water's acidity, salinity and temperature.
Higher carbon-dioxide levels in the atmosphere change all these things. The gas's mere presence acidifies seawater. Its warming effects alters its temperature, and by melting ice changes the salinity, too. Sources of ambient noise such as winds, waves and whales are all affected. And the changes all differ from place to place.
To work out the consequences for submariners, a team led by Andrea Gilli of the NATO Defence College in Rome and Mauro Gilli of ETH Zurich used computer modelling to examine how sound travelled through deep water in the past (from 1970 to 1999) and how climate models suggest it will do so in the future (from 2070 to 2099).
The researchers originally published their findings in the Texas National Security Review in 2024. In the North Atlantic, a crucial battleground between Russian subs and NATO sub-hunters—as well as in the area between the first and second island chains in the Western Pacific, just to the east of Japan, Taiwan and the Philippines—detection will become harder. In the Bay of Biscay, off the French coast, a sub that could once be detected from 60km away will be spotted only at 20km.
In the Sea of Japan, however, local conditions will make life easier for the hunters. North Korean submarines operating in those waters at a depth of 100m could previously get to within 10km away without detection. In the future, estimate the authors, they could be seen from 45km off.
The hypothetical scenario the study considers is based on a worst-case outcome in which nothing has been done to reduce greenhouse-gas emissions; a trajectory most scientists now consider unrealistic. All the same, the trends identified in the paper are noteworthy. In recent years there has been much talk of new detection methods making the oceans more transparent. In fact, argue the authors, the seas might become more opaque.
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