41% Of Planet's Oceans Experienced January Heatwaves; Oceans Already Irrevocably Changed On Human Timescale

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Even after nearly three months of winter, the oceans of the Northern Hemisphere are disturbingly warm. Last summer’s unprecedented temperatures—remember the “hot tub” waters off the coast of Florida?—have simmered down to a sea-surface average around 68 degrees Fahrenheit in the North Atlantic, but even that is unprecedented for this time of year. The alarming trend stretches around the world: 41 percent of the global ocean experienced heat waves in January. The temperatures are also part of a decades-long hot streak in the oceans. “What we used to consider extreme is no longer an extreme today,” Dillon Amaya, a research scientist at the National Oceanic and Atmospheric Administration’s Physical Sciences Laboratory, told me.

The situation is expected to worsen. Research suggests that by the end of the century, much of the ocean could be in a permanent heat wave relative to historical thresholds, depending on the quantity of greenhouse gases that humans emit. Many other changes will unfold alongside those hot ocean temperatures: stronger hurricanes, rising sea levels, unmanageable conditions for marine life. Our seas, in other words, will be altered within decades.

Many detailed climate projections focus on the state of the oceans by 2100, a short time frame that allows for relative certainty. “That’s what policy makers want to know about,” Sandra Kirtland Turner, a paleoceanography professor at UC Riverside, told me. It’s also a year in which many people being born today will still be living, witnessing the consequences of what we’re doing currently. But Earth has many, many millennia ahead of it, and that deep future is being shaped by the burning of fossil fuels happening right now. If we continue down the path we’re on, Earth’s oceans may be irrevocably transformed over the next several hundred years. Imagine yourself in space, hovering over the planet as an astronaut would, a few centuries from now. “The ocean will still be blue and beautiful,” Amaya said. But even from space, you’d know something was different. And the closer you got to the waves, the more clearly you’d see how things went awry.

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Closer to Earth’s surface, familiar coastlines would be gone, buried under encroaching seas. If emissions continue as they are for another century, sea levels may be nearly 50 feet higher in the 2500s, according to some researchers. A bird’s-eye view would reveal signs of fish and marine mammals tracing new paths through once-icy waters, and quiet zones in the once-bustling tropics. Hundreds of years from now, polar seas might be particularly attractive to marine fauna for several reasons: First, warmer seas absorb less oxygen, even as slowed-down currents inhibit the natural mixing between the shallow and deep parts of the ocean, preventing the oxygen that does get absorbed from reaching the depths. Growing stratification also prevents deep-sea nutrients from rising to the marine life that needs them in the upper oceans. Hundreds of years from now, many species might adjust to these conditions by migrating poleward, toward colder waters. (Some of this redistribution is already happening.) By 2300, Earth may experience “a significant, fundamental reorganization of the ocean ecosystem,” and a “catastrophic collapse” of fisheries, Matthew Long, a climate scientist at the National Center for Atmospheric Research who runs a nonprofit dedicated to techniques for removing carbon dioxide from ocean environments, told me.

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https://thinc.blog/2024/03/20/the-oceans-have-already-changed/