Read here, here, here, here and here. A clown-like PNAS peer-reviewed study by a group of green professors, none of whom are climate or atmospheric scientists (Robert K. Kaufmann, Heikki Kauppi, Michael L. Mann, and James H. Stock) purports to explain how the IPCC's climate scientists and their climate models got it sooo wrong in regards to the well documented lack of global warming since 1998.
Their theory, widely reported by both an uncritical mainstream media and compliant, gullible bloggers & pundits, is that China's growing coal use emitted the needed sulfur emissions to stop global warming during the past 10 years. Unfortunately, it's a clownish theory based on, at best, flimsy, pretend climate science and minimal actual empirical evidence.
1. Unlike annual compiled CO2 emissions and CO2 monthly atmospheric levels, recent sulfur emissions and SO2 atmospheric aerosol levels are guesstimates. This study is based on guesstimates, which are based on tenuous assumptions, which are likely not a reflection empirical reality.
2. It is estimated by these authors that coal sulfates increased around 2004, well after the global non-warming phase had already started.
3. Unlike climate-impacting volcano sulfate aerosol ejections that travel multiple kilometers into the upper atmosphere (stratosphere), sulfate emissions (aerosol particles) from coal remain in the lower atmosphere and are resident only for a short time as they are quickly washed out of the air by precipitation ("acid rain").
4. Coal sulfate emissions are not well mixed in the atmosphere, which means they are not well distributed around the globe meaning their global impact on temperatures is severely limited.
5. A previous NASA satellite measurement analysis published by atmospheric experts found no increase in global aerosol optical depth over the years 2000 through 2006.
6. Despite China's large increase in coal burning, aggregate global sulfate emissions have dramatically decreased because worldwide coal plants are burning coal with less sulfur and newer smokestack (flue) scrubber technology.
7. The empirically measured impact of coals' SO2 on temperatures is not settled, with science research suggesting that sulfur aerosols in the lower atmosphere are actually a cause of warming, not cooling.
8. Natural ocean and atmospheric oscillations are significantly better explanations of the non-global warming over the 1998-2008 period than the lame, meritless, speculative sulfur emissions hypothesis.
9. In another NASA study, it was found that aerosol particulates in the atmosphere have declined since the 1990's.
Aggregate coal SO2 emissions adjusted for use of cleaner coal and use of improved scrubber tecnhology, declining overall, everywhere (source):
Aerosol (including SO2 particulates) optical depth comparisons from satellite measurements for years 2001, 2004, and 2008. Little change over several years of Kaufmann et al. study, and satellite data reveals aerosols to be of a local/regional concern, not a global issue (source):
Study's authors own graphical representation of their estimate of SO2 warming/cooling impact (purple curve) on global temperatures (blue curve). Even their own assessment would indicate little, if any, impact from human sulfur emissions during span of 1998 to 2008 (source).
The above graph has all curves removed except for global temperatures and sulfur forcing. Below, the SOI (index of the Southern Oscillation) curve (green) is added back to the study's original graph.
Focusing on the blue box representing the period analyzed by the study, one quickly sees that both the SOI and global temps are highly variable. Looking closer, there is a relationship evident between the SOI and temperatures - when the SOI heads in one direction, the global temps head in the opposite direction a few months later.
Apparently, the authors of this study chose to ignore Gaia's Southern Oscillation (and/or other major ocean/atmosphere oscillations) despite its obvious influence on cooling global temps from 1998 to 2008. Instead they focus on the purple curve (sulfur emissions forcing) that just as obvious had a fraction of Gaia's impact on temperatures.
As Judith Curry (a renowned climate scientist) states:
"I don’t find this explanation to be convincing because the increase in sulfates occurs only since 2004 (the solar signal is too small to make much difference). Further, translating regional sulfate emission into global forcing isnt really appropriate, since atmospheric sulfate has too short of an atmospheric lifetime (owing to cloud and rain processes) to influence the global radiation balance...the authors have put forward one possible explanation for the lack of warming, but an explanation associated with natural internal variability associated with the ocean oscillations is at least as plausible as the explanation put forward by the authors."