A warming planet doesn't just affect the quality of the air – the oceans are also heating up at an alarming rate, which can bleach coral, melt glaciers and raise the sea level. While this is hardly news to anybody, it turns out that the problem may be much worse than we initially thought. A new study has used a more accurate technique to measure the rate of ocean warming, and found that it could be 60 percent higher than the current worst-case scenario suggests.
Previous studies measured changes in ocean temperature by way of Argo, a network of robotic sensors that float in the oceans the world over and keep an eye on things. While this system is incredibly precise and will be useful going forward, its data only goes back to 2007, so it can't place readings in their historical context.
To take a wider snapshot of the warming ocean, a new study led by researchers at the Scripps Institution of Oceanography looked to the air instead. The working principle behind the study is that as water warms up, it releases more oxygen and carbon dioxide into the atmosphere. By calculating the combined amount of those two gases in the air – a figure it calls atmospheric potential oxygen (APO) – the team is able to get an idea of how much heat the ocean is holding.
Of course, a warming ocean isn't the only factor at play in that figure – burning fossil fuels is largely what got us into this mess in the first place, and other natural processes contribute too. But after accounting for those other factors, the team was able to single out the warming ocean's influence, and by extension its heat-energy content.
The study estimated that the world's oceans absorbed more than 13 zettajoules of heat energy each year between 1991 and 2016. That's about 150 times more energy than humans produce as electricity in a year, the team says.
Unfortunately, it's also about 60 percent higher than was estimated by the recent report released by the United Nations Intergovernmental Panel on Climate Change (IPCC), which already painted a pretty grim picture of the path we're on.
"Imagine if the ocean was only 30 ft (9 m) deep," says Laure Resplandy, lead author of the study. "Our data shows that it would have warmed by 6.5℃ (11.7℉) every decade since 1991. In comparison, the estimate of the last IPCC assessment report would correspond to a warming of only 4℃ (7.2℉) every decade."
Thanks to that extra warming, the new study concludes that we humans would need to reduce carbon dioxide emissions by a further 25 percent, in order to avoid the worst effects of climate change. Given our current trajectory and the fact that studies seem to keep finding grimmer outlooks, that's pretty worrying.
The study was published in the journal Nature.
UPDATE (Nov. 14/18): Study co-author Ralph Keeling has issued the following statement: I am working with my co-authors to address two problems that came to our attention since publication. These problems, related to incorrectly treating systematic errors in the O2 measurements and the use of a constant land O2:C exchange ratio of 1.1, do not invalidate the study's methodology or the new insights into ocean biogeochemistry on which it is based. We expect the combined effect of these two corrections to have a small impact on our calculations of overall heat uptake, but with larger margins of error. We are redoing the calculations and preparing author corrections for submission to Nature.
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