Climate change isn't just about temperature. The main driver is the return to the atmosphere of millions of years worth of sequestered carbon in the form of carbon dioxide released from the burning of fossil fuels, but that CO 2 doesn't just increase the heat retention of the atmosphere; it also dissolves into the oceans. Unfortunately, a paper published in PNAS this week examines this effect and finds that it's happening faster than previously predicted.

As you may remember from early chemistry lessons, when CO 2 dissolves in water it decreases the pH, thereby making the water more acidic. The problem with this is that marine organisms have evolved over time to tolerate a quite narrow pH band. For those organisms that like to wear their skeletons on the outside, it's seriously bad news.

Shellfish, coccolithophores, corals, and many others beside have external shells or skeletons made of calcium carbonate. As the oceans acidify, it becomes harder to form these shells or skeletons, and existing ones begin to dissolve. Sadly, that's exactly what we're seeing, with huge consequences for marine ecosystems that are already ravaged by pollution and massive overfishing.

The authors of the new paper, a team from the University of Chicago, measured the pH of coastal waters around Tatoosh island, off the coast of Washington in the Pacific Northwest. Over the course of eight years, they made nearly 25,000 measurements, and their data reveals aspects of oceanic pH regulation that were previously unknown.

In contrast to the prevailing theory that oceans represent a stable, well-buffered solution, the scientists discovered that there was a distinct diurnal cycle. pH would fall during the day as photosynthesis occurred, but then increased (as much as 0.25 points) at night when photosynthesis stopped. That much is both new and interesting. What's also new, but much more worrying, is the trend over time.

Across the eight years of the study, the authors found that marine pH was decreasing much faster than simulations predicted. In fact, this decrease is around an order of magnitude faster. With marine habitats already under extreme environmental stress, this is the last thing they need. The team also monitored the populations of local shellfish and algae; the former declined as pH fell, while the latter benefited.

The research suggests that we need to move away from our current practice of adding billions of tons of carbon dioxide to the atmosphere each year. Fortunately, there are a number of good plans out there, such as Google's Clean Energy 2030, but does the worldwide political will exist to implement any of them?

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