The Complexity of Earth's Oceans
The ocean stores more heat than the atmosphere, moves carbon on a scale no engineering project matches, and remains less mapped than the surface of Mars. What scientists are learning is changing how climate is understood.
The Daily Edition2 min read
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- What happened
- A global fleet of thousands of autonomous floats, satellites measuring sea level to millimeters, and deep-sea mapping efforts have transformed oceanography over two decades. The ocean has absorbed about 90 percent of the excess heat trapped by greenhouse gases and roughly a quarter of human carbon emissions.
- Why it matters
- The ocean sets the pace of climate change. How much heat and carbon it takes up, and how its circulation responds, determines how fast the surface warms and how high seas rise.
- What remains uncertain
- Whether major circulation systems are slowing, how fast the deep ocean is warming, and how ocean ecosystems will respond to simultaneous warming, acidification and oxygen loss.
The ocean covers seven-tenths of the planet, holds almost all of its water, and until recently was studied mainly from ships that sampled a tiny fraction of it. That changed with a program that put thousands of robotic floats into the sea. Each sinks to two kilometers, drifts, rises while measuring temperature and salinity, and transmits its data to a satellite before diving again.
The result is the first continuous picture of the ocean's interior. It shows unambiguously that the ocean is warming, and that it has absorbed about nine-tenths of the extra heat trapped by greenhouse gases. Without that absorption, surface temperatures would have risen far faster.
The carbon pump
The ocean also takes up roughly a quarter of the carbon dioxide people emit each year. Some dissolves directly; some is taken up by plankton whose remains sink. This uptake slows climate change and acidifies seawater, which harms organisms that build shells. Whether the uptake will continue at the same rate as the ocean warms is one of the central uncertainties in climate projections.
Circulation
Great currents move heat from the tropics toward the poles. In the Atlantic, warm surface water flows north, cools, sinks and returns south at depth. Measurements suggest this circulation has weakened; whether that is a trend or natural variation is contested, and the consequences of a substantial slowdown for European weather and sea level would be large.
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The ocean has absorbed about 90 percent of the excess heat trapped in the climate system.
Fact · confidence high
- IPCC AR6 WGI · IPCC
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