Photograph by Mario Tama, Getty
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People gather on a hot winter day on Ipanema beach on September 8, 2017 in Rio de Janeiro, Brazil. According to NOAA, global temperatures over the first six months of 2017 were the second-highest on record.

Photograph by Mario Tama, Getty

2017 Was the Hottest Year Yet In the World's Ocean

Warming ocean waters can have harmful impacts on habitats like coral reefs and sea ice, to name a few.

Oceans aren't likely to cool any time soon, a new study finds.

In fact, 2017 was the warmest year on record in the ocean, according to researchers from the Chinese Academy of Sciences.

Their findings indicate a "long-term warming trend driven by human activities."

The study measured the rising temperature of the ocean as a whole, but the Atlantic and Antarctic Oceans, they found, experienced the most warming.

The scientists looked at ocean temperature data that researchers from various institutions, including NOAA in the U.S., began collecting in the 1950s. Starting in the late 1990s, ocean temperatures began to take off.

Ocean temperatures in 2017 measured hotter than 2015, the previous hottest year on record.

By looking at global data spanning a decades-long time period, researchers hoped to get an accurate picture of warming trends that accounted for weather anomalies. Ocean temperatures in 2016, for example, were lower than in 2015 and 2017 because of a huge El Niño weather event that cooled waters.

So What?

Beachgoers wading in the surf likely won't notice the gradual temperature rise, and down-the-line atmospheric impacts can be hard to visualize. But that doesn't mean a warming ocean won't have real, harmful impacts.

In their study, researchers called out coral bleaching and melting sea ice as victims of warming oceans.

Coral bleaching occurs when corals—stressed by heat, light, or pollution—expel the symbiotic algae they need to be healthy. Without them, corals can starve. One sobering study released earlier this month found the window to save them is rapidly closing.

While all hope may not be lost for sea ice, the Arctic's cover has been slowly disappearing in the past few decades. Since satellites began measuring sea ice coverage and thickness in 1979, there's been a decrease in both.

The researchers also called out declining ocean oxygen as a potential impact from warming waters. Earlier this month, a new study found that some fish are avoiding certain parts of oxygen-depleted ocean because the waters are essentially suffocating them.

Rising sea levels, more intense storms, and unstable marine habitats susceptible to disease are all other possible effects scientists say we could see from warming ocean temperatures.

In an op-ed about the study written for the Guardian, a professor of thermal science at the University of St. Thomas noted that "If you want to understand global warming, you need to first understand ocean warming."

What's Causing It?

Greenhouse gases like carbon dioxide and methane have been credited with driving warming temperatures, by trapping more heat closer to the Earth's surface. One study published in 2016 found that for every ton of CO2 not emitted, 32 square feet of Arctic ice could be saved.

The pollutants already emitted in our atmosphere, however, could still take decades to disseminate.