This chart of ocean temperatures should really scare you

If you were to dip your toes into the middle of the North Atlantic — say, somewhere between South Carolina and Spain — the water would feel frigid. You definitely wouldn’t want to swim. It’s winter.

Yet that water would, in fact, be very warm, relatively speaking. Right now, the North Atlantic ocean is, on average, warmer than any other time on record, running about 2 degrees Fahrenheit hotter than the average temperature over the last three decades.

To understand just how unusual this is, take a look at the chart below. The wave of squiggly lines represents the sea surface temperature, averaged across the North Atlantic, from 1981 to now; each squiggle is a different year.

Courtesy of Brian McNoldy (using data from NOAA)

The thick orangey-red line that runs the length of the chart and hovers above nearly all the others is from 2023. The North Atlantic started breaking heat temperature records in March of last year.

Even more alarming is the departure that the new, shorter line from 2024 represents. It’s far above the rest, indicating this extreme, anomalous increase has continued into this year.

“It’s significantly warmer than it ever has been for this time of year,” Brian McNoldy, a climate researcher at the University of Miami’s Rosenstiel School, told Vox. “This is deeply troubling,” he recently wrote on X.

All this heat is not only a problem for marine ecosystems today, scientists say. It’s also a warning of what could come — including what could put human life in harm’s way.

What’s heating up the Atlantic?

A warm Atlantic is one signal that the planet, as a whole, is heating up. There are others: This year, large stretches of the US are experiencing a “lost winter” with record-warm temperatures (Minneapolis-St. Paul reached a record 65 degrees earlier this week). NASA, meanwhile, recently confirmed that 2023 was the hottest year on record.

A new study in the journal Nature Climate Change indicates that the planet has already surpassed 1.5 degrees Celsius of warming, a limit set by the 2015 Paris Agreement to avoid the worst impacts of climate change. (The study was based on sea sponges, a large category of very cool and useful marine animals.)

Jennifer Adler for Vox

Fueling this warming are our cars, power plants, and farms, which have blanketed Earth with heat-trapping greenhouse gases. Remarkably, 90 percent or so of that added warmth is absorbed by the oceans; without them, we’d be even more screwed.

A handful of more obscure reasons help explain why the North Atlantic, specifically, has been so hot, as my colleague Umair Irfan writes. Some regions of the Atlantic have been less windy, for example. That wind not only cools the ocean surface but sends sand and dust from the Sahara out to sea, where it scatters sunlight back out to space (which further helps cool down the ocean). Ironically, a drop in air pollution — which is ultimately a good thing — may also be helping heat up the ocean.

Who cares about a hot ocean?

The plankton! The fish! The whales! And hopefully — you!

Wildlife, on the whole, is really good at adapting to environmental change, but warming is happening too fast. It’s altering the growth, the location, and perhaps even the color of plankton communities, which are made up of tiny marine organisms that literally every ocean animal relies on. Plankton that endangered North Atlantic right whales eat, for example, are moving north, and the whales are following them. That makes some of the protected areas that are stuck in space (where activities that harm the whales are limited) less useful.

The heat is making some fish smaller. Some fisheries, meanwhile, are shifting toward the poles, in some cases pushing them into different political territories. That’s a problem for the people who eat fish and the $253 billion US fishing industry. What’s more, ocean heat can wipe out coral reefs almost overnight, as I know too well — threatening the enormous tourism and fishing industries that these ecosystems support.

A hot winter in the Atlantic could also be a bad sign for this year’s hurricane season. “Warm February sea surface temperatures do often correlate with active hurricane seasons,” meteorologist Jeff Berardelli wrote earlier this month. Forecasts suggest that, in the coming months, El Niño might transition into a La Niña, a weather phenomenon that creates hurricane conditions in the Atlantic. “All signs point to an active hurricane season,” Berardelli wrote.

So, yeah. Super hot ocean = bad.

And unfortunately, forecasts also suggest that this anomalous warmth in the North Atlantic won’t let up anytime soon, McNoldy said. Come summer, already hot water in parts of the Atlantic, such as the Caribbean, will likely be even hotter — again, portending a scary season for coral reefs and hurricanes.

If there’s any good news here it’s that we are better than ever at predicting these changes. That means we have some time to prepare. Marine biologists can try to breed more heat-tolerant corals, for example, as they’ve been doing. Governments can ready funds for hurricane damage. But the frustrating thing is that short of getting big companies and wealthy countries to cut back on carbon emissions, solutions like these only amount to never-ending damage control.