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Earth’s Hot Oceans Are a Cosmic Tragedy

Earth’s Hot Oceans Are a Cosmic Tragedy

The ocean off the coast of southern Florida is having a long, hot summer. For weeks, surface temperatures hovered around 90 degrees Fahrenheit, before dropping to the 80s last week. The world’s third-largest barrier reef is dying, and scientists are fishing out coral samples and bringing them to the cool safety of laboratory tanks. One spot along the coastline hit triple-digit temperatures last month, conditions you would expect inside a hot tub. Some coastal Floridians skipped their usual dips in the ocean because it didn’t seem appealing anymore.

Marine heat waves—periods of persistent and anomalously high temperatures of surface seawater—have materialized in other parts of the world too. The surface temperatures of about 44 percent of Earth’s oceans are currently experiencing extreme heat, according to the National Oceanic and Atmospheric Administration. Some of that warming is to be expected, because 2023 is an El Niño year. But “all of these marine heat waves are made warmer because of climate change,” Dillon Amaya, a research scientist at NOAA’s Physical Sciences Laboratory, told me. June was already a record-breaking month for the world’s oceans, and then July came along and topped it. According to the experimental forecast system that Amaya and his colleagues run at NOAA, half of the world’s oceans may be in the throes of a heat wave by September.

Earth is an ocean planet, a water world. We have not observed anything like it yet in the universe, not even with our best telescopes, and so we cannot know exactly how rare—and thus, how difficult—it may be for the forces of cosmic nature to produce such a thing. And yet, here we are, simmering its oceans at our peril and changing the fundamental makeup of the ecosystem that defines Earth. Our oceans have absorbed most of the excess heat produced by greenhouse-gas emissions in recent decades, serving as a buffer that protects us from the worst effects of climate change. Humans may be sweltering on land this summer, but our planet’s future—and therefore ours—is intimately tied with the sea.

Astronomers have spent years searching for worlds beyond our solar system that might host oceans, in the hopes that they also host life. Of the more than 5,000 planets they’ve found, only a few are in the habitable zone—at the right distance from their star to be conducive to liquid, flowing water. And scientists have yet to confirm that any rocky, Earth-size planets are also wet. Part of the problem is that oceans are difficult to detect with the technology available to researchers today. Our planet may be slick with rolling seas, but “if we were to observe Earth as an exoplanet, from a different system, we could not measure that Earth has water,” Charles Cadieux, an astronomer at the University of Montreal, told me.

Other oceans exist in our very own solar system but are hidden beneath the surface of icy moons, their exact composition unknown to us. Krista Soderlund, a research scientist at the University of Texas at Austin, studies Europa, a moon of Jupiter with a salty subsurface ocean that could harbor microbial life; she spends her days marveling at this other ocean world, all while worrying about the one she lives on. “I don’t really have a way to reconcile that,” Soderlund told me. “You can see the short, rapid changes right now, and then I’m looking forward to how that’s going to affect my kids. How much worse is it going to be?”

Next year, NASA is scheduled to launch the mission that Soderlund is working on: a spacecraft that will reach Europa in 2030. The vessel will carry a plaque engraved with a poem written by the U.S. poet laureate, which reads in part, “O second moon, we, too, are made / of water, of vast and beckoning seas.” This idea of connection, a touch of intimacy in an unfamiliar cosmos, is lovely. Read another way, it sounds almost like an elegy. We are made of vast seas. But when those seas are superheated, dissolving the shells and skeletons of marine creatures and enabling toxic blooms of algae, they beg for relief more than they beckon.

Our planet did not start out with seas. They came later, after Earth had cooled down from its formative molten years. How Earth got its water remains an open question; some researchers believe that it arrived inside asteroids that bombarded Earth several billion years ago, while others suggest that it was locked within the planet since it first formed out of the mountain-size rocks whizzing around the early solar system. This September, a NASA spacecraft will bring home samples from an asteroid that has remained unchanged since that cosmic period, and the rocky bits and pieces could reveal crucial information about our very existence. Scientists hope to uncover clues about the forces that gave rise to Earth’s oceans and enriched them with the chemical compounds that eventually sparked life.

In the face of climate change, the thrill of discovery is tinged with melancholy; as we learn more about how our ocean planet came to be, we’re subjecting its waters to intense heat, and the entire planet is facing the consequences. Hot oceans are melting ice sheets, intensifying hurricanes, and devastating fishing industries. “The Earth has seen a lot of change in its life,” Karen St. Germain, the director of NASA’s Earth-science division, told me. “But we are driving it now in a way that it hasn’t been driven before.”

Astronomers refer to the habitable region around a star as the Goldilocks zone. There, conditions are not too hot and not too cold, but just right for water to lap on alien shores. Earth is squarely in our sun’s habitable zone, and will enjoy its pleasant perch for at least another few billion years, until the sun grows hot enough to truly boil the planet’s oceans away. But Earth may become unlivable long before that: floods, droughts, wildfires, days so hot that touching asphalt can severely burn your skin, hot-tub seas that can roil coral and humans alike.

Last week, the head of the United Nations said, “The era of global warming has ended; the era of global boiling has arrived.” Climate scientists have cautioned that global boiling is not a scientific term, and that our current spate of extreme weather has been predicted for years. This is global warming, they say, and it’s plenty dramatic. Still, boiling can help emphasize the visceral urgency of what’s happening in the water. Because it is getting more difficult each day to look around and feel that things here are just right.

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