For a whole month this year, the world’s atmosphere contained more than 400 parts per million of carbon dioxide, on average. That’s more CO2 than the atmosphere has seen for hundreds of thousands of years, and those levels just keep going up.
All that carbon in the atmosphere means hotter global temperatures and more severe weather, of course. But scientists have less of an idea of what climate change will do to the ocean—a complex, difficult-to-study realm that’s due for huge chemical and ecological shifts. And that’s worrying, because the oceans are also a big carbon sink and the source of sustenance for most life on Earth.
Some changes are pretty certain, says Charlie Stock, a climate modeler at NOAA’s Geophysical Fluid Dynamics Lab. The ocean of the future will be warmer than it is today. And its structure will also be different—less-dense warm water will stack on top of a layer of cold water, with less mixing between the two. “Ocean productivity is basically bringing together nutrients and light,” Stock says. Deeper water has more nutrients; the surface gets more light. If less often the twain shall meet, overall productivity could go down.
And a warming ocean jumbles up where animals can survive. Fish tend to follow the water that’s just the right temperature for them, so eventually, Stock says, tropical fish could end up in normally temperate waters. Some species’ habitats will get squeezed—especially animals adapted to very specific conditions at the poles. And critters at the equator have to deal with ocean temperatures that are warmer than they’re used to.