What is the average lifetime of atmospheric CO2?

Excerpt from this post:

[See this story]

An emailed comment on the above:

Just incredible.

For one thing, where does Hansen get off calling PlayStation simulations "climate studies"?

For another thing - and this demands some focus - Hansen claims that a fifth of CO2 stays in the air for a thousand years. Okay, the IPCC puts each year's natural carbon emissions in the neighborhood of 200 billion metric tons. By Hansen's metric, this means that the oceans, dissolving rocks and plants will not see 40 billion of that till a thousand years have ended. Yet the IPCC also says that more than 98% of all carbon emissions - artificial and natural combined - are re-absorbed by oceans, dissolving rocks and plants each year.

So try to reconcile both of these models. Of the yearly 207 billion that go up (fresh), 166 come down (fresh and stale), plus 38, the tail end of the atmosphere's carbon contents before the First Crusade captured Jerusalem. Does that sound plausible?

What Hansen is implicitly foistering, of course, is that nature discriminates against artificial CO2 and leaves it in the air while the rest gets recycled normally. But nature would do just the opposite. Fossil fuels are rich in the very carbon isotopes that plants prefer, since fossil fuels are the remains of plants themselves. As for rocks, they'll dissolve under rainwater no matter which carbon isotopes it contains, and the ocean will continue to follow its complex cycles of CO2 absorption and emission.

10 years, more or less. Every empirical study puts that as the average lifetime of atmospheric CO2.