The oceans are acidifying at the fastest rate in 300 million years. How worried should we be?

The oceans are acidifying at the fastest rate in 300 million years. How worried should we be?.

 

There’s reason for alarm here: Studies have found that acidifying seawater can chew away at coral reefs and kill oysters by making it harder to form protective shells. The process can also interfere with the food supply for key species like Alaska’s salmon.

But it’s not fully clear what this all adds up to. What happens if the oceans keep acidifying and water temperatures keep rising as a result of global warming? Are those stresses going to wipe out coral reefs and fisheries around the globe, costing us trillions (as one paper suggested)? Or is there a chance that some ecosystems might remain surprisingly resilient?

That’s one of the big outstanding questions on climate change. “We understand the physics of simple things like how oceans become acidic,” said Richard Norris, a paleobiologist at Scripps Institution of Oceanography, UC San Diego. “But when it comes to how ecosystems might react, that’s big and complex and messy, with all these interactions going on, both physiological and how organisms interact with each other.”

How to study acidification’s effects

Broadly speaking, there are two ways that scientists can try to study the effects of ocean acidification — and both have limitations. First, they can examine various species in laboratories or in the field and see how corals and molluscs and fish respond to changes in ocean pH levels. The downside is that it’s hard to see how these species might adapt (or not) over the longer run.

Another approach is to examine the fossil record. There have been multiple periods in the Earth’s history where atmospheric carbon dioxide levels rose sharply (for natural reasons) and the oceans became warmer and more acidic. That includes the Paleocene–Eocene Thermal Maximum, an era 55 million years ago with greenhouse-gas concentrations in the atmosphere roughly comparable to what the Earth could soon face.

In a recent paper for Science, Norris and his co-authors found that this ancient world had few coral reefs, a poorly oxygenated ocean, and drastically different food chains that had difficulty sustaining large predators like sharks and whales. On the flip side, “the extinction of species was remarkably light, other than a mass extinction in the rapidly warming deep ocean.” So that’s one possible glimpse into our future:

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