A new report recently published in the journal Nature suggests the Earth's oceans are absorbing more of the planet's excess heat than previously thought.
Scientists have known for some time that oceans store excess heat energy, and this helps keep the planet in its balmy, just-right temperature for supporting the explosion of life on Earth.
Knowing how hot the ocean is getting, and how fast that temperature is rising, helps scientists understand more about human-impacted climate change. It helps them know how much excess energy is being produced, and it helps them predict how much heat the ocean is capable of absorbing and how much warming will be felt on the Earth's surface.
Up until the report was issued this week, the Intergovernmental Panel on Climate Change (IPCC) thought it had a pretty good handle on how much excess energy the oceans were absorbing. Using those numbers, the panel set targets for the amount of carbon reduction necessary to slow, and ultimately reverse, potentially devastating planetary warming.
But these new numbers suggest those targets may have to be revised upward by 25 percent. Research by the study's lead author, Princeton professor Laure Resplandy, indicates our oceans are absorbing about 60 percent more heat energy than previously estimated.
According to Resplandy, the world's oceans have taken up more than 13 zettajoules of energy every year between 1991 and 2016. A joule is the standard unit of energy; a zettajoule is one joule, followed by 21 zeroes.
"Imagine if the ocean was only 30 feet deep," Resplandy said. "Our data show that it would have warmed by 6.5 degrees Celsius every decade since 1991. In comparison, the estimate of the last IPCC assessment report would correspond to a warming of only 4 degrees Celsius every decade."
How they got the new numbers
It's not that the old numbers were wrong; it's that the new numbers relied on new techniques and new ways to measure ocean warming. The old techniques used spot measurements of ocean temperature. But Resplandy and her team measured the amount of oxygen and carbon in the air, a number they call "Atmospheric Oxygen Potential (APO)." As oceans warm, they release oxygen and carbon into the atmosphere, which increases APO.
Another factor that raises APO is the burning of fossil fuels. Resplandy and her team compared the expected rise in APO due to the burning of fossil fuels, and compared it to the actual APO they were seeing. By looking at the difference, the team was able to predict how much carbon and oxygen were being released by the oceans and, therefore, how warm the world's oceans were getting.
Why the new numbers matter
A host of countries, including the U.S. and China, signed the Paris Climate Accord in 2015, which aims to keep average global temperatures from rising more than 2 degrees Celsius above pre-industrial levels. Many climate scientists predict that if temperatures go above that mark, humans will be faced with devastating long-term global affects. Keeping those temperatures down requires cutting the amount of greenhouse gases pumped into the atmosphere.
The U.S. has since pulled out of that climate agreement, but most of the rest of the world remains focused on limiting the rise of the world's average temperatures.
This new research suggests that accomplishing that goal requires countries to pull 25 percent more carbon out of the atmosphere than they've already committed to cleaning up.