Good question, north, but I do not know the answer. What I do know is that one major volcano eruption can easily outweigh everything mankind is doing with respect to CO2 for a substantial period of time. This article by Professor Ian Klimer is on point: http://www.dailymail.co.uk/debate/article-1231673/Global-warming-Dont-wait-The-Earth-tricks-carbon-count-control.html Regards, Dew