The oceans of the world have been transformed into a true sponge for our emissions, and new climate models suggest that we have passed them on immediately.
Since the 1950s, the vast water bodies of our planet have absorbed about 93 percent of the energy in the climate system, and although most of this warming has been observed near the surface of the ocean, rising temperatures now allow even the deepest parts .
True world data on the deep ocean is hard to reach, but a new estimate, based on recent measurements and nearly a dozen climate models, suggests that climate change has already affected about half (20 to 55 percent) of the Atlantic, Pacific Ocean, and Indian Ocean.
What’s more, in just six decades, these man-made changes in temperature and salinity could very well spread to 80 percent of the world’s oceans.
“We were interested in whether the levels of temperatures and salt were large enough to overcome natural variability in these deeper areas,” explains climate scientist Yona Silvy of the Sorbonne University in France. “That is, if they were increased higher than they were ever during the normal peaks and troughs.”
Using temperature and salinity measurements from the deep ocean and plugging these into 11 current climate models, the team simulated ocean and atmospheric circulation over the years, with and without the contribution of human emissions.
In the second half of the 20th century, Silvy and her colleagues found human warming responsible for most observed ocean changes – “statistically” and “untimely” other than what would occur naturally. Because heat and salt affect the density and circulation of the ocean, this can have far-reaching implications.
“This is affecting global ocean pollution, rising sea levels, and is a threat to human societies and ecosystems,” Silvy said.
Most of the time, heat and salt are transported from the surface of the ocean relatively slowly to the interior of the ocean, which means that many of the deepest parts experience a delay in changes by humans.
However, some deeper areas circulate faster, and thus respond more quickly to our emissions.
In the new model, for example, the Southern Ocean, which is relatively well ventilated, experienced changes caused by humans relatively freely, as appeared as early as the 1980s.
Meanwhile, the oceans in the Northern Hemisphere took a little longer to respond, with most changes calculated to appear sometime between 2010 and 2040.
Together, by 2020, the model shows somewhere between 20 percent and 55 percent of the world’s oceans have been altered by anthropogenic climate change.
By mid-century, these changes could reach 50 to 60 percent of the world’s oceans, and by 2080 55 to 80 percent.
“This work suggests that much of the observed patterns of change in the interior of the ocean have been induced by humans and will continue to intensify with sustained CO2 emissions,” the authors write.
Plus, even if emissions are slower, the slowdown in ocean circulation means we’m locked into a certain number of changes that move forward.
We still do not understand the relationship between deeper changes in salt and heat and surface warming, or how these changes affect ocean circulation. It requires much more research, especially in the southern hemisphere where deep ocean data are not much and far in between, but we need to research.
The study was published in Nature Climate change.
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