The second installment of the IPCC's 4th Assessment on Climate Change, titled "Impacts, Adaptation and Vulnerability", will be released on April 6, 2007. In recognition of this report, I'm doing a weekly series called "Climate Dangers You May Not Know About".
Everyone knows that carbon dioxide (CO2) warms the globe. But many people don't know about its other dangerous effect. The build-up of CO2 is undermining ocean life through "ocean acidification". I'll start by explaining why our oceans are becoming more acidic, and then illustrate why this is so dangerous to ocean life and our entire food chain.
When CO2 in the atmosphere dissolves into the ocean, as naturally happens, it forms carbonic acid. As CO2 concentrations increase from the burning of fossil fuels, more CO2 is dissolved into the ocean. In one sense this is a good thing because the dissolved CO2 can't act as a greenhouse gas to warm the planet. But it's also a bad thing, because it changes the pH balance of the ocean – the degree to which the ocean is acidic or alkaline ("basic").
The natural state of the ocean is a weak base (the opposite of acid). This environment is great for the many forms of ocean life that use calcium carbonate to form their skeletons or shells. These range from familiar species such as corals and shellfish, to less well-known creatures like the tiny one-celled algae called coccolithophores. Ocean acidification makes it harder for these "calcifying organisms" to maintain themselves.
You can see why yourself with a simple experiment. Calcium carbonate comes in many forms. In addition to comprising the shells of sea creatures, it's the primary component in chalk, lime, and marble. Take a piece of chalk and put it in a glass of water. It will just sit there – a wet piece of chalk. Now slowly pour in some vinegar – an acid. The water will start to bubble, emitting CO2, and the chalk will dissolve.
This is an exaggerated example of what's happening in the ocean. The ocean isn't as acidic as a glass of water with vinegar, so calcifying organisms aren't actually dissolving in front of our eyes. But the ocean's increased acidity makes it harder for them to form healthy shells and skeletons.
As the ocean’s acidity increases from the build-up of CO2, corals and shellfish lose calcium. This isn't just a problem of aesthetics, that scuba divers won't have pretty coral reefs to look at. Coral reefs provide habitat for many of the world’s fish, and a billion or more people depend upon fish as their main source of protein.
There is also the possibility of a climate feedback. Coccolithophores are covered by calcium carbonate plates. Because the plates are white and the coccolithophores hang out near the ocean surface, these creatures act as tiny mirrors reflecting sunlight away from the Earth's surface. It's possible that ocean acidification, by decreasing the abundance of coccolithophores, could decrease the reflectivity of the Earth and thus accelerate global warming.
In this NASA photo, what looks like clouds in the water
is actually the reflected light from billions of coccolithophores.
Ocean acidification is one of the most serious consequences of increased CO2 in the atmosphere, yet no one talks about it. And this is not the only under-reported consequence. Next week I’ll tell you how global warming can spread disease by fouling our drinking water.