This article was written 19 years ago, and pretty much ignores any political elements associated with the topic, probably because it was written 19 years ago.
"Through a million year period, the average amount of carbon dioxide in the atmosphere is affected by four fluxes: flux of carbon due to (1) metamorphic degassing, (2) weathering of organic carbon, (3) weathering of silicates, (4) burial of organic carbon. Degassing reactions associated with volcanic activity and the combining of organic carbon with oxygen release carbon dioxide into the atmosphere. Conversely, the burial of organic matter removes carbon dioxide from the atmosphere."
http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html