Earth's oceans absorb a whopping 93% of the extra heat that greenhouse gases trap in the atmosphere.
A new study has revealed that this absorption process is happening far faster than scientists had realized.
In one sense, the oceans' heat-trapping abilities help us in the short term.
"If the ocean wasn't absorbing as much heat, the surface of the land would heat up much faster than it is right now," Malin Pinsky, an associate professor of ecology and natural resources at Rutgers University, told the New York Times. "In fact, the ocean is saving us from massive warming right now."
But overall, warmer oceans are a major problem. More heat in the water can negatively impact marine species, kill coral reefs, fuel sea-level rise, and lead to more severe storms. The authors of the new study calculated that in a "business-as-usual" scenario - in which we continue emitting greenhouse gasses as projected - rising ocean temperatures would lead sea levels to rise a full foot between now and the year 2100.
That's because water, like most things, expands when it's heated. This thermal expansion is one of the driving forces behind sea-level rise; even small changes in temperature results in a large increase in water volume.
A handful of studies about ocean temperature since 2014 have conflicted with the IPCC numbers. So this new analysis looked at four such studies and concluded that some adjustments in how ocean heat gets measured were to blame for the discrepancy.
Zeke Hausfather, one of the study's co-authors and a graduate student at the University of California, Berkeley, told Berkeley News that 2018 "will most certainly be the warmest year on record in the oceans, as was 2017 and 2016 before that." (Though the final calculations for last year aren't in yet.)
As ocean temperatures continue to increase, we'll see more coastal flooding because of sea-level rise, as well as heavier rainfall and more severe hurricanes.
That's because hurricanes' wind speed is influenced by the temperature of the water below. A 1-degree Fahrenheit rise in ocean temperature can increase a storm's wind speed by 15 to 20 miles per hour, according to Yale Climate Connections.
Higher ocean temperatures can also cause corals to expel the algae living in their tissues and turn white - what's known as coral bleaching. This increases their mortality risk, along with that of the many species that live in and around reefs.
People who rely on fish for food could be affected too, Kathryn Matthews, deputy chief scientist for the conservation group Oceana, told the New York Times.
"The actual ability of the warm oceans to produce food is much lower, so that means they're going to be more quickly approaching food insecurity," she said.
Climate scientists have long had their eyes on ocean temperatures as a definitive indicator of how our planet's climate is changing as a result of the greenhouse gases that human activity sends into the atmosphere. Whereas surface temperatures can fluctuate year to year thanks to short-term weather patterns or things like volcanic eruptions, ocean temperatures don't.
Before Argo, ocean temperature collection was more piece-meal - scientists would sometimes send sensors down to watery depths, but these sensors would transmit data only once before sinking to the bottom forever.
"Scientists are continually working to improve how to interpret and analyze what was a fairly imperfect and limited set of data prior to the early 2000s," Hausfather told Berkeley News. "These four new records that have been published in recent years seem to fix a lot of problems that were plaguing the old records, and now they seem to agree quite well with what the climate models have produced."
These new findings align with research published in November 2018 that also indicated (despite a few corrections after publication) that scientists had been underestimating ocean warming.
"For each of the past 25 years, oceans have absorbed an amount of heat energy that is 150 times the energy humans produce as electricity annually," the Scripps Institution of Oceanography reported.
Heat isn't the only troublesome thing oceans are absorbing. They also thanklessly take in roughly 25% of the carbon dioxide we emit. According to 2017 study, the oceans have absorbed about 40% of all carbon dioxide emissions since the beginning of the industrial era. Think of them as Earth's air purifiers.
As Michael Crosby, president of Mote Laboratory and Aquarium, previously put it to Business Insider: "You like to breathe? Estimates are that up to 80% of the oxygen you are breathing in right now comes from the ocean."