The God Species_ How the Planet Can Survive the Age of Humans - Mark Lynas [108]
Homo sapiens currently releases 10 billion tonnes of carbon per year—a million tonnes every hour. Since James Watt’s invention of the steam engine in 1784, humans have released more than half a trillion tonnes of carbon from geological safe storage underground into the atmosphere.1 Up to 85 percent of this liberated carbon, somewhere between 340 and 420 billion tonnes, has soaked into the oceans.2 This is a stroke of luck for us, because rates of greenhouse warming are sharply reduced as a result: Were the oceans not performing this free service, the Earth’s temperature would be rising at double or triple today’s rate. But it is a service the oceans perform at a substantial cost to themselves, for by holding on to dissolved carbon dioxide they begin to change their chemical composition. The process is straightforward, involving what U.S. marine biologist Richard Feely calls “irrefutable chemistry.” To see the process in action, drop a piece of chalk into a glass of carbonated water. Why does the chalk dissolve in an angry froth of bubbles? Because carbon dioxide forms carbonic acid when it dissolves in water, and this acidic solution attacks the alkaline calcium carbonate that makes up chalk. The chemical equation is simple: CO2 + H2O = H2CO3 (carbonic acid).
The result is that, everything else remaining equal, the extra carbonic acid depletes seawater of the dissolved carbonate minerals that many marine creatures, from corals to plankton to sea urchins, use to build their shells or skeletons.3 This “other CO2 problem” is now considered so crucial that one group of experts suggests ocean acidification “could represent an equal (or perhaps even greater) threat to the biology of our planet” than climate change alone.4 What the future holds is uncertain, as this chapter will show. As with climate change, we can base predictions on the educated guesses provided by computer models and also peer into the Earth’s deep geological past. My conclusion is straightforward. Even if there were no climate change, we would still have to get rid of CO2—urgently—because ocean acidification presents a serious threat to the integrity of the marine biosphere.
INDUSTRIAL OCEANS
At the dawn of the Anthropocene, at the end of the eighteenth century, the preindustrial world oceans had a pH of about 8.2. Today ocean pH has dropped to 8.1 units and continues to fall. This may not seem like a big deal, but the pH scale (like the Richter scale for earthquakes) is logarithmic, so this small-sounding tenth-of-a-unit change translates into a 30 percent rise in acidity in our seas.5 As with the other planetary boundaries, we now have plenty of scientific data confirming the nature and magnitude of this change. The gradual acidification of the oceans is being constantly monitored at many different locations: At Station ALOHA in Hawaii researchers have observed a decreasing pH trend of 0.0019 units per year, precisely tracking the rise in atmospheric CO2 measured since the 1950s not far away on the summit of the Mauna Loa.6 Equal trends of rising acidity have been measured off the Canary Islands and Bermuda.7 While ocean pH fluctuates naturally, just like the weather, the ongoing trend toward acidification is as clear as that toward global warming. There is no significant doubt about what is happening, or the cause.
Again as with global warming, acidification “hot spots” have begun to emerge at discrete locations in the world’s oceans. Particularly vulnerable are west-facing continental coastlines, where water that is already naturally more acidic wells up from the depths. One group of scientists has discovered that “corrosive acidified water” has reached 50–100 meters closer to the surface off the western United States, and that the trend is worsening rapidly.8 Because colder water dissolves more CO2