ABSTRACT
Four hundred million years ago, carbon concentrations in the atmosphere were between 3,000 and 7,000ppm, a figure that puts our present concern over reaching 400ppm, or even 450ppm, into perspective. The planet naturally absorbs and stores large quantities of carbon as part of the natural carbon cycle, and in much greater amounts than the small proportion taken up in semi-permanent, geological form. The earth continually both absorbs and emits carbon through both natural and man-made (anthropogenic) processes. In 1990, carbon emissions were double the Earth's capacity to absorb them, and the annual excess balance of 3.2GtC/yr was added to the only place that would and could take it the atmosphere. Sun provides the power that enabled photosynthesis to capture the carbon loose in the atmosphere over the early Earth. Current estimates suggest there is a total live biomass of 560Gt of carbon on the Earth, with a primary production (and decay) rate of about 105GtC/yr.
