percent annually. As a result of all this, the concentration of carbon
dioxide in the air today—a little over four hundred parts per million—is
higher than at any other point in the last eight hundred thousand years.
Quite probably it is higher than at any point in the last several million
years. If current trends continue, CO 2 concentrations will top five
hundred parts per million, roughly double the levels they were in
preindustrial days, by 2050. It is expected that such an increase will
produce an eventual average global temperature rise of between three
and a half and seven degrees Fahrenheit, and this will, in turn, trigger a
variety of world-altering events, including the disappearance of most
remaining glaciers, the inundation of low-lying islands and coastal cities,
and the melting of the Arctic ice cap. But this is only half the story.
Ocean covers seventy percent of the earth’s surface, and everywhere
that water and air come into contact there’s an exchange. Gases from the
atmosphere get absorbed by the ocean and gases dissolved in the ocean
are released into the atmosphere. When the two are in equilibrium,
roughly the same quantities are being dissolved as are being released.
Change the atmosphere’s composition, as we have done, and the
exchange becomes lopsided: more carbon dioxide enters the water than
comes back out. In this way, humans are constantly adding CO 2 to the
seas, much as the vents do, but from above rather than below and on a
global scale. This year alone the oceans will absorb two and a half billion
tons of carbon, and next year it is expected they will absorb another two
and a half billion tons. Every day, every American in effect pumps seven
pounds of carbon into the sea.
Thanks to all this extra CO 2 , the pH of the oceans’ surface waters has
already dropped, from an average of around 8.2 to an average of around
8.1. Like the Richter scale, the pH scale is logarithmic, so even such a small
numerical difference represents a very large real-world change. A decline
of .1 means that the oceans are now thirty percent more acidic than they
were in 1800. Assuming that humans continue to burn fossil fuels, the
oceans will continue to absorb carbon dioxide and will become