It’s easy for us land dwellers to forget that we live on a water planet, more than 70% of it covered by a vast ocean. But we are entering an age—or more accurately, have created an age—when that fact will be impossible to ignore. With global climate change, the seas are rising, yes, but they are also warming, slowly but steadily, and that warmth is now reaching levels that can drive profound changes here on land. Many of those changes have begun, many are on display this year, and some will have seismic consequences going forward.

Almost as shocking as the scale of these changes are the Trump administration’s efforts to dismantle the very scientific instruments that enable us to understand them. We’ll get there. But first, a little immersion into our water planet to better understand what it means to overheat it and force the ocean to compensate.

Earth, Despite the Name, Is a Water Planet

A more representative, less terra-centric view of our 70% water planet. (Photo by NOAA/NASA GOES via Smithsonian)

A quick refresher on Earth’s ocean. I mean, where did it even come from, all this water?

After Earth’s molten formation 4.6 billion years ago, the planet gradually cooled below the boiling point of water and, fueled by steam released from volcanoes, it rained for thousands of years, filling the low-lying surface of the planet. An era of bombardment by icy asteroids provided a huge additional volume of water. And voila, a water planet was born, almost entirely covered by one massive ocean. Tectonic activity eventually produced large land masses and, over time, both plate movement and global temperature fluctuations have greatly changed the shape of the ocean—and the land, our default perspective—e.g., tying more or less water up in ice. But with the exception of a couple of global ice ages, the liquid ocean has always dominated Earth’s surface. We’ve almost always been a “blue planet,” and always a water planet.

Water Manages Heat—and Thus Life—on Earth

This water was the birthplace of life on Earth. Indeed, water is considered the birthplace of carbon-based life anywhere, which is why scientists search for it in other solar systems. It took at least 500 million years for the first life to form in the ocean (~4.1 billion years ago), and once it did, life remained simple and aquatic for the vast majority of Earth’s history. It took fungi, plants, and especially animals big evolutionary leaps to venture out of the ocean (and much of it did not; today, nearly 80% of Earth’s animal life, measured in biomass, lives in the oceans), first to the tidal zone, then the coasts, and even today, with terrestrial life spanning most dry land, the ocean continues to exert tremendous influence on that life. It does this through a range of mechanisms. Chief among them, our ocean plays the dominant role in managing the Earth’s heat and making large regions of the planet habitable.

The ocean has spared us land dwellers from the true ~36°C consequences of our fossil-fuel burning actions. And we can’t tackle 1.5°C?

A core way the ocean does this is by absorbing solar radiation at tropical latitudes and distributing that heat via vast ocean currents to cooler parts of the world. These currents then distribute water that has cooled at the poles back toward the equator. Without this mechanism, the heat that makes life possible even in the otherwise frigid latitudes would remain concentrated around an intolerably hot equator. In this sense, the oceans are a great regulator of the global climate, tamping down extremes and supporting Goldilocks-style just-right regional climates around the world.

The oceans are also the primary source of moisture and precipitation—basically, weather—to land. As the sun heats ocean surface water, it evaporates, creating humid air that is transported by forces like winds and the Earth’s rotation, delivering precipitation, the water that makes terrestrial life possible.

So, if the role of the ocean in managing Earth’s temperature is fundamental to life on Earth, what happens when we overheat it?

The Ocean: an Unfathomably Huge Heat Buffer

A depiction of how the Earth has dealt with the energy imbalance created mainly by burning fossil fuels and adding heat-trapping molecules to the atmosphere. The oceans have spared us the true brunt of global warming, storing 91% of excess heat, up from 89% when this visual was created three years ago.(Graphic by Copernicus)

The ocean is estimated to have absorbed 91% of the excess heat, caused mainly by the burning of fossil fuels, that has been trapped in the Earth’s atmosphere. This heat storage is possible because of the ocean’s specific heat capacity—i.e., water takes a lot more energy to warm than land or air. Direct absorption of sunlight, the main way the ocean absorbs heat, depends on the level of albedo present, where darker surfaces, like the ocean surface, absorb more of the sun’s energy than light surfaces, like polar ice caps, which reflect it back to space. But other mechanisms, like heat exchange with the atmosphere, warm the ocean, too.

Without that excess-heat absorption and storage in recent decades, life on land would have been thrown into chaos (at best) by skyrocketing temperatures by now. According to one study, the heat taken up by the upper layer of the ocean between 1955 and 2010 was enough to warm the atmosphere by a jaw-dropping 36°C. This massive, climate-mediating role of the ocean puts our thus-far unsuccessful human efforts to keep warming to 1.5 or 2°C in sharp relief. That is, the ocean has spared us land dwellers from the true ~36°C consequences of our fossil-fuel burning actions. And we can’t tackle 1.5°C?

The Buffer Is Getting Thin

The vastness of the ocean means it requires tremendous inputs to respond. But the excess heat that carbon emissions have trapped since the start of the Industrial Revolution is one such tremendous input. Major recent research captures the scale in this way, according to one of a new study’s 50 authors, John Abraham: the heat absorbed by the ocean in 2025 alone is “like 12 Hiroshima bombs being detonated each second, for every minute, hour, and day for the entire year.”

The absorption of that heat means that the average temperature of the oceans has been steadily rising, and now those temperatures are reaching levels that fuel impacts, including on land, that we will be unable to ignore.

Overall, the ocean has broken average temperature records every year for the past nine years. Temperatures have increased most at the surface, where sea surface temperatures have warmed roughly 0.8°C between 1901 and 2020, and recently broke new monthly........

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