evidence: It turns out that while much of the "pulse" of extra CO2 accumulating in the atmosphere would be absorbed over the next century if emissions miraculously were to end today, about 20 percent of that CO2 would remain for at least tens of thousands of years. [...] Determining the residence time of carbon dioxide in the atmosphere is a rather complex problem. A common misconception arises from simply looking at the annual carbon flux and the atmospheric stock; after all, with 230 gigatons absorbed by the oceans and land every year, and a total atmospheric stock of 720 gigatons, one might expect the average molecule of CO2 to remain in the atmosphere for only three to four years. Such an approach poorly frames the issue, however. It is not the residence time of an individual molecule that is relevant. What really matters is just how long it will take for the stock of anthropogenic carbon emissions that has accumulated in the atmosphere to be reabsorbed.