By Bob Berwyn, InsideClimate News
Mar 11, 2017
The rate of ocean warming has nearly doubled since 1992 compared with the previous three decades. And the warming has reached deeper waters, scientists reported Friday.
The findings are important because the world's oceans provide one of the best records of the excess energy trapped on Earth by increased greenhouse gases, largely from the burning of fossil fuels. As the seas heat up from climate change, the water expands and rises, causing coastal flooding and, in Antarctica, ice shelves to disintegrate.
The researchers, from NOAA, the National Center for Atmospheric Research, the University of St. Thomas and the Chinese Academy of Sciences, found that between 1960 and 2015 total ocean warming was 13 percent greater than the most recent estimate by the Intergovernmental Panel on Climate Change (IPCC), whose periodic reviews influence the actions of governments.
After 1992 the rate at which the oceans warmed nearly doubled. Most of the warming is in the tropical Atlantic and Pacific Oceans, as well as the Southern Ocean, surrounding Antarctica.
According to the study, ocean warming now accounts for as much as 50 percent of global sea level rise.
They found that the warming accelerated in the mid-1970s. In the 1990s, the warming spread to deeper waters, from 700 to 2,000 meters. The biggest increases in ocean heat content were in those deeper layers, showing "that the deep ocean has played an increasingly important role in the ocean energy budget since 1998," according to the study. The Atlantic Ocean heat content increase was about 3.5 times greater than the Pacific, despite being less than half the size.
The world's oceans absorb more than 90 percent of the heat trapped by greenhouse gases, storing it for centuries. Eventually some of the heat is released to the atmosphere and warms adjacent land masses.
The ocean warming directly influences ocean ecosystems and seasonal currents.
The two studies are not directly related, but the deeper warming tracked by Trenberth's team is "interesting for humans from a food point of view," Henson said. Large tuna and other commercially valuable fish, as well as keystone species like sharks and whales, spend parts of their lives in that zone, where temperatures have generally been stable for thousands of years.