A strong scientific consensus now exists that human emissions of greenhouse gases have important climatic consequence, and that these consequences, as well as the impact on ecological balances from direct physiological effects on vegetation, will grow in the future. A primary cause of these changes is the increase in atmospheric CO2, which is emitted to the atmosphere by burning of fossil fuels, changes in land use such as deforestation. Carbon dioxide is inert in air and thus is not removed by chemical breakdown in the atmosphere.

Nevertheless, only about half of the CO2 released to the atmosphere since the begining of the industrial revolution remains there. The portion removed has been taken up and stared in oceans and on land, by processes that we refer to as "sinks". Studies to identify and understand sinks have emerged as critical for assesing long-term changes in atmospheric concentrations in the past, and will dramatically enhance understanding how the earth's climat will envolve in the future.

Atmospheric CH4 is second only to CO2 as an anthropogenic greenhouse gas. A molecule of CH4 may contribute more than 20 times as much as a molecule of CO2 to radiative forcing, and CH4 is also a key species in the chemistry of atmosphere. Methane was, untly recently, the most rapidly increasing greenhouse gas, rising 145 % since the begining of the industrial revolution. After years of near-steady growth averaging about 12 ppbv/year (1991, 1998) to 0 ppbv (2000). The long-term increase and curently variable growth rates are not well understood, we cannot presently predict future increases or decreases with confidence.