National Geographic : 2011 Apr
• Castello Aragonese. Even before we got into the water, some impacts were evident. Clumps of barnacles formed a whitish band at the base of the island's wave-battered cli s. "Barnacles are really tough," Hall-Spencer observed. In the ar- eas where the water was most acidi ed, though, they were missing. We all dived in. Buia was carrying a knife. She pried some unlucky limpets from a rock. Search- ing for food, they had wandered into water that was too caustic for them. eir shells were so thin they were almost transparent. Bubbles of carbon dioxide streamed up from the sea oor like beads of quicksilver. We swam on. Beds of sea grass waved beneath us. e grass was a vivid green; the tiny organisms that usually coat the blades, dulling their color, were all miss- ing. Sea urchins, commonplace away from the vents, were also absent; they can't tolerate even moderately acidi ed water. Swarms of nearly transparent jellyfish floated by. "Watch out," Hall-Spencer warned. " ey sting." Jelly sh, sea grass, and algae---not much else lives near the densest concentration of vents at Castello Aragonese. Even a few hundred yards away, many native species can't survive. e wa- ter there is about as acidi ed as the oceans as a whole are forecast to be by 2100. "Normally in a polluted harbor you've got just a few species that are weedlike and able to cope with widely uctuating conditions," Hall-Spencer said once we were back on the boat. "Well, it's like that when you ramp up CO ." SINCE THE START of the industrial revolution, enough fossil fuels---coal, oil, and natural gas--- have been burned and enough forests cut down to emit more than 500 billion tons of CO . As is well known, the atmosphere has a higher con- centration of CO today than at any point in the past 800,000 years and probably a lot longer. What is less well known is how carbon emis- sions are changing the oceans too. e air and the water constantly exchange gases, so a por- tion of anything emitted into the atmosphere eventually ends up in the sea. Winds quickly mix it into the top few hundred feet, and over centuries currents spread it through the ocean depths. In the 1990s an international team of scientists undertook a massive research project that involved collecting and analyzing more than 77,000 seawater samples from di erent depths and locations around the world. e work took 15 years. It showed that the oceans have ab- sorbed 30 percent of the CO released by hu- mans over the past two centuries. ey continue to absorb roughly a million tons every hour. For life on land this process is a boon; every ton of CO the oceans remove from the atmo- sphere is a ton that's not contributing to global warming. But for life in the sea the picture looks di erent. e head of the National Oceanic and Atmospheric Administration, Jane Lubchenco, a marine ecologist, has called ocean acidi cation global warming's "equally evil twin." e pH scale, which measures acidity in terms of the concentration of hydrogen ions, runs from zero to 14. At the low end of the scale are strong acids, such as hydrochloric acid, that release hy- drogen readily (more readily than carbonic acid does). At the high end are strong bases such as lye. Pure, distilled water has a pH of 7, which is neutral. Seawater should be slightly basic, with a pH around 8.2 near the sea surface. So far CO emissions have reduced the pH there by about 0.1. Like the Richter scale, the pH scale is logarithmic, so even small numerical changes represent large e ects. A pH drop of 0.1 means the water has become 30 percent more acidic. If present trends continue, surface pH will drop to around 7.8 by 2100. At that point the water will be 150 percent more acidic than it was in 1800. e acidi cation that has occurred so far is probably irreversible. Although in theory it's possible to add chemicals to the sea to counter the e ects of the extra CO , as a practical mat- ter, the volumes involved would be staggering; it would take at least two tons of lime, for example, to o set a single ton of carbon dioxide, and the Elizabeth Kolbert wrote last month about the idea that human impacts on the planet will long outlive us. David Liittschwager's photos of life in one cubic foot of soil or sea appeared in February 2010.