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Ocean heat is climbing 40% faster than thought

Trends in ocean heat from 4 different observational datasets, compared to the CMIP5 computer model mean, from 1955 through 2017. Data: Cheng et al. Science, 2019; Chart: Lazaro Gamio/Axios.

New, independent observations from ocean buoys and other data sources show Earth's oceans are warming at a rate that's about 40% faster than indicated in the 2013 U.N. Intergovernmental Panel on Climate Change (IPCC) report.

Why it matters: The study, published Thursday in the journal Science, resolves a key uncertainty in climate science by reconciling analyses from a variety of different scientific teams.

The oceans are absorbing about 93% of the extra heat going into the climate system. So far, most of that heat resides in the upper ocean, and is only slowly diffusing down into deeper waters. Faster warming is already resulting in tangible, harmful impacts, from coral bleaching across the Great Barrier Reef to rapidly intensifying hurricanes.

  • Scientists describe the ocean as having a "long memory," meaning that the heat going into the waters now will continue to be released long after humans cut greenhouse gas emissions (assuming we do take that course).

Be smart: The data from four different research groups now generally match the ocean heat content projections from the newest climate models, the study finds, which indicates that these models are accurately simulating the Earth's radiation budget.

  • “We can see the emergence of the signal of global warming much more clearly in ocean heat content,” says study co-author Zeke Hausfather, an energy systems analyst at the climate research group Berkeley Earth.
  • Hausfather says 2018 will be the warmest year on record for the Earth's oceans, beating the record set just last year.

How it works: Because the ocean's heat content doesn't vary as sharply as surface temperatures, it is considered a more reliable indicator of global warming.

The impact: Warmer oceans are already causing unprecedented back-to-back coral bleaching events, and are contributing to sea-level rise. They're also causing glaciers to melt from below in Greenland and Antarctica.

  • Warmer waters provide critical fuel for extreme storms, with studies showing ties between Hurricane Harvey's devastating deluge and warmer than average waters in the Gulf of Mexico, for example.

Why you'll hear about this again: The oceans are a main reason why climate change will not relent even if emissions were to cease today, since they will continue to release heat, and also greenhouse gases, over time. There are also implications for carbon removal technologies, which are getting more attention from scientists and investments from major oil companies.

Lost in much of the discussion on carbon removal, however, is the potential for the oceans to spoil the party.

“The climate system has a long memory," Hausfather says, “It doesn’t warm as quickly as it otherwise would and it’s a lot harder to cool it back down once it starts warming.”

  • The bottom line: "Just like the oceans buffer the rate of warming, they would also similarly buffer the rate of cooling in a world where we had net-negative emissions," Hausfather says.

He cited a 2016 study that showed it would take slightly more negative emissions to reduce warming than it takes positive emissions to increase temperatures.