If it wasn’t for our oceans, we would be well and truly screwed. Not only do they absorb heaps of our carbon emissions, but we also rely on them to soak up over 90 percent of excess heat energy.
However, a new study has suggested that we have massively underestimated the amount of heat absorbed by our oceans in recent decades. The researchers on the project warn that this suggests Earth is actually more sensitive to fossil-fuel emissions than we previously thought.
Reporting in the journal Nature, a team led by Scripps Institution of Oceanography and Princeton University estimated that the ocean has absorbed 60 percent more heat over the past 25 years than the figure in the United Nations IPCC Climate Change report released last month.
The IPCC Climate Change report argued that we must aim to keep global average temperatures 1.5℃ (2.7F) below pre-industrial levels because even a 2℃ (3.6℉) increase will have far-reaching consequences for biodiversity, society, and the planet. To avoid this, we need to cut our carbon emission ASAP. These findings suggest that must be reduced by 25 percent more than what was previously estimated.
“Imagine if the ocean was only 30 feet deep,” lead author Laure Resplandy, a Princeton assistant professor of geoscience, said in a statement. “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.”
Scientists work out surface warming with the knowledge that the ocean takes up roughly 90 percent of all the excess energy produced as the Earth warms. If more heat is going into the oceans than we realized, that also means that our greenhouse gas emissions are trapping more heat than we thought. From this, we can conclude that the Earth is more sensitive to fossil-fuel emissions than anticipated.
This, the paper's authors write, "suggests that ocean warming is at the high end of previous estimates, with implications for policy-relevant measurements of the Earth response to climate change, such as climate sensitivity to greenhouse gases and the thermal component of sea-level rise."
Of course, quantifying ocean heat uptake is an unbelievably complex feat itself. Researchers previously measured this using millions of measurements from a network of robotic sensors across the world known as Argo. This new approach used high-precision oxygen and carbon dioxide measurements to infer ocean temperature increase. It showed that the ocean has soaked up over 13 zettajoules ( or 13,000,000,000,000,000,000,000 joules) of heat energy each year between 1991 and 2016.