Most of us understand that what we give off in the form of exhaust - from cars and manufacturing and energy production and burning forests - makes its way into the atmosphere, and is responsible for changes in the global climate. What is less familiar is the fact that the oceans are absorbing as much as a third of the carbon dioxide being emitted into the atmosphere.

The effects are already being felt. That added carbon dioxide is slowly making the oceans less alkaline and more acidic, altering the chemical balance on which much of oceanic life depends. Carbon dioxide reacts with seawater to form carbonic acid, a process that consumes carbonate ions. Those ions are necessary for the chemical reaction used to form calcium carbonate, the structural element in corals and the shells of many marine animals.

As the oceans acidify, shells will simply dissolve. The growth of coral reefs will slow, and their structural integrity would be weakened, making them more vulnerable to storms and erosion. That would be a catastrophic loss. The list of potential long-term effects to oceanic life is only beginning to be explored.

Scientists have understood ocean acidification for a long time. But what they are learning now is how quickly it is increasing, in step with increases in atmospheric carbon dioxide. New studies show that if carbon dioxide emissions continue at current rates, shells and corals could begin to dissolve - especially in the southern oceans - within 30 years.

Combating a change as fundamental as this requires a fundamental change in awareness and behavior. A third of whatever we emit in the way of carbon dioxide ultimately drains to the ocean, which is all the more reason to curb emissions quickly.