The contemporary and historical budget of atmospheric CO2

Observations of CO2 and O-2 are interpreted to develop an understanding of the changes in the abundance of atmospheric CO2 that have arisen over the period 1995-2007. Fossil fuels accounted for an addition of 89.3 Gt of carbon to the atmosphere over this time period, 29% of which was transferred to the ocean, 15% to the global biosphere, with the balance (57%) retained by the atmosphere. Analysis of historical data for CO2 derived from studies of gases trapped in ice at Law Dome in Antarctica indicate that the biosphere represented a net source of atmospheric CO2 prior to 1940, switching subsequently to a net sink.