By JR on Tuesday, July 05, 2011
It does two things that most Warmists avoid or deny: Admit that there has been no global temperature rise in the 21st century and that natural factors play a big role in global temperature variations -- as big a role as their theorized CO2 effect. Excerpt only below. Key point: They say that aerosols from coal burning have cancelled out the CO2 effect. Yet the data show NO rise in global aerosols
A new paper has been published in PNAS entitled “Reconciling anthropogenic climate change with observed temperature 1998-2008.”
Given the widely noted increase in the warming effects of rising greenhouse gas concentrations, it has been unclear why global surface temperatures did not rise between 1998 and 2008. We find that this hiatus in warming coincides with a period of little increase in the sum of anthropogenic and natural forcings. Declining solar insolation as part of a normal eleven-year cycle, and a cyclical change from an El Nino to a La Nina dominate our measure of anthropogenic effects because rapid growth in short-lived sulfur emissions partially offsets rising greenhouse gas concentrations. As such, we find that recent global temperature records are consis- tent with the existing understanding of the relationship among global surface temperature, internal variability, and radiative forcing, which includes anthropogenic factors with well known warming and cooling effects.
The key argument in their paper is that an increase in coal burning (primarily in China) has increased atmospheric sulfate concentration with a resulting global cooling effect.
Sulfate from coal burning is but one source of atmospheric aerosol. AGW Observer provides a recent list of papers on aerosol forcing observations. See especially the Remer et al. paper, Fig 5, which shows no trend in global aerosol optical depth during the period 2000-2006. A plot for East Asia also shows no trend regional aerosol optical depth.
I also checked to see what CMIP5 is using for aerosol forcing, see here, but there doesn’t seem to be any simple way to visualize whatever is being used. I found a paper by Jones et al., see Fig. 10, that appears to be the CMIP5 aerosol forcing. Looking at the black curves (historical, to 2005), it is seen that sulfur dioxide emissions peaked during 1960-1980, and then have steadily decreased (a tiny uptick after 2005 is seen in some of the future scenarios). Fossil fuel black carbon has shown a stead increase since 1950, as has fossil fuel organic carbon. I don’t seen any signal in the total aerosol emissions that resembles the coal emissions with a flat trajectory since 1985 and an uptick after 2004 (although the historical data ends in 2005).
Judith Curry comments: Their argument is totally unconvincing to me. However, the link between flat/cooling global temperature and increased coal burning in China is certainly an interesting argument from a political perspective. The scientific motivation for this article seems to be that that scientists understand the evolution of global temperature forcing and that the answer is forced variability (not natural internal variability), and this explanation of the recent lack of warming supports a similar argument for the cooling between 1940 and 1970. The political consequence of this article seems to be that the simplest solution to global warming is for the Chinese to burn more coal, which they intend to do anyways.
And finally, with the civil heretic discussion fresh in my mind, I checked the personal web pages of each of the co-authors: Robert K. Kaufmann, Heikki Kauppi, Michael L. Mann (not Michael E. Mann, of hockeystick fame), and James H. Stock. These authors (individually and collectively) apparently know a heck of a lot less about atmospheric aerosols (i.e. pretty much nothing) than Freeman Dyson knows about climate change. The authors don’t seem to know much about attribution, either.