I think you're asking how long it takes for the atmosphere's CO
2 level to fall back to its old value after we've dumped some extra CO
2 in. It's not any one exact time, because the process is gradual, mainly involving uptake of CO
2 by the slowly circulating oceans.
Sometimes there's confusion about the CO
2 lifetime, because the time it takes for an individual molecule to get taken up somewhere on the surface is usually less than 100 years. However, the overall balance between the atmosphere and all the deep oceans takes longer to restore. A typical time scale is around 1000 years, although some recovery happens more quickly.
Another important part of our carbon footprint comes from methane, a much stronger greenhouse gas than CO
2. Methane doesn't last as long, since it's mostly converted to CO
2 in less than 20 years.
Mike W.
(published on 09/08/2011)
