The simplest way to remove carbon dioxide, the main greenhouse gas, is to grow plants - preferably trees, since they tie up more of the gas in cellulose, meaning it will not return to the air within a season or two. Plants build themselves out of air and water, taking only a tiny fraction of their mass from the soil.

In coastal waters rich in runoff, plankton can swarm densely, a million in a drop of water. They color the sea brown and green where deltas form from big rivers, or cities dump their sewage. Tiny yet hugely important, plankton govern how well the sea harvests the sun's bounty, and so are the foundation of the ocean's food chain.

Like the ocean, land plants hold about three times as much carbon as the atmosphere. While oceans take many centuries to exchange this mass with the air, flora take only a few years.

Gregory Benford Quotes