By monitoring the color of reflected light via satellite, scientists can determine how successfully plant life is photosynthesizing. A measurement of photosynthesis is essentially a measurement of successful growth, and growth means successful use of ambient carbon.

Until now, scientists have only had a continuous record of photosynthesis on land. But following three years of continual data collected by the SeaWiFS instrument, NASA has gathered the first record of photosynthetic productivity in the oceans. The process begins with a measurement of surface chlorophyll concentration.

Chlorophyll is the material that allows plant cells to convert sunlight into energy, thus enabling them to grow. It's a green substance, and thus a good indicator of overall plant health: robust forests and lush lawns and vibrant phytoplankton blooms appear green. By measuring chlorophyll concentration, scientists can determine the health and growth of plants in a given area. By extension, healthy color signatures indicate the successful use of carbon, the fundamental building block for life. In other words, lots of green indicates lots of chlorophyll; lots of chlorophyll implies healthy photosynthesis; strong photosynthesis indicates growth, and growth indicates successful use of carbon.