Reply To: Questions regarding DPF.

[mchargue]

From the introduction:
—–
Of the current 10 billion tons of carbon (GtC) emitted
annually as CO2 into the atmosphere by human activities
[Boden et al., 2009; Houghton, 2008], only around 40%
[Jones and Cox, 2005] remain in the atmosphere, while the
rest is absorbed by the oceans and the land biota to about
equal proportions [Bopp et al., 2002]. This airborne fraction
of anthropogenic CO2 (AF) is known to have stayed
remarkably constant over the past five decades [Jones and
Cox, 2005], but if it were to increase in a way predicted by
models, this could add another 500 ppm of CO2 to the
atmosphere by 2100 [Friedlingstein et al., 2006], significantly
more than the current total.
—–

From my reading, I see that the airborne fraction is (remarkably) constant. That is to say, the same. If the fraction is not changing, then it’s not increasing. I can see where the verbiage about ‘40% remaining in the atmosphere’, though, might make it sound like we’re adding 40% or our total CO2 production to the atmosphere each & every year. However, if that were the case, then the fraction would be changing – which is a point the authors seem to making.

Failing a chance to speak with the author, I think we’re stuck with our interpretations. I hope that more evidence – one way of the other – comes out soon.

Pat