A paper published today by James Hansen has some startling admissions, including
- the effect [forcing] of man-made greenhouse gas emissions has fallen below IPCC projections, despite an increase in man-made CO2 emissions exceeding IPCC projections
- the growth rate of the greenhouse gas forcing has "remained below the peak values reached in the 1970s and early 1980s, has been relatively stable for about 20 years, and is falling below IPCC (2001) scenarios (figure 5)."
- the airborne fraction of CO2 [the ratio of observed atmospheric CO2 increase to fossil fuel CO2 emissions] has decreased over the past 50 years [figure 3], especially after the year 2000
- Hansen believes the explanation for this conundrum is CO2 fertilization of the biosphere from "the surge of fossil fuel use, mainly coal."
- "the surge of fossil fuel emissions, especially from coal burning, along with the increasing atmospheric CO2 level is 'fertilizing' the biosphere, and thus limiting the growth of atmospheric CO2."
- "the rate of global warming seems to be less this decade than it has been during the prior quarter century"
According to "coal death train" Hansen,
"However, it is the dependence of the airborne fraction on fossil fuel emission rate that makes the post-2000 downturn of the airborne fraction particularly striking. The change of emission rate in 2000 from 1.5% yr-1 to 3.1% yr-1 (figure 1), other things being equal, would have caused a sharp increase of the airborne fraction (the simple reason being that a rapid source increase provides less time for carbon to be moved downward out of the ocean's upper layers).
We suggest that the huge post-2000 increase of uptake by the carbon sinks implied by figure 3 is related to the simultaneous sharp increase in coal use (figure 1).
We suggest that the surge of fossil fuel use, mainly coal, since 2000 is a basic cause of the large increase of carbon uptake by the combined terrestrial and ocean carbon sinks. One mechanism by which fossil fuel emissions increase carbon uptake is by fertilizing the biosphere via provision of nutrients essential for tissue building, especially nitrogen, which plays a critical role in controlling net primary productivity and is limited in many ecosystems."
So is the new data we present here good news or bad news, and how does it alter the 'Faustian bargain'? At first glance there seems to be some good news. First, if our interpretation of the data is correct, the surge of fossil fuel emissions, especially from coal burning, along with the increasing atmospheric CO2 level is 'fertilizing' the biosphere, and thus limiting the growth of atmospheric CO2. Also, despite the absence of accurate global aerosol measurements, it seems that the aerosol cooling effect is probably increasing based on evidence of aerosol increases in the Far East and increasing 'background' stratospheric aerosols.
Both effects work to limit global warming and thus help explain why the rate of global warming seems to be less this decade than it has been during the prior quarter century."
James Hansen, Pushker Kharecha and Makiko SatoShow affiliations