In our paper
Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell, W. Rossow, J. Schaake, J. Smith, S. Sorooshian, and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union
hypothesis 2a reads
Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and involve a diverse range of first order climate forcings, including, but not limited to, the human input of carbon dioxide (CO2). Most, if not all, of these human influences on regional and global climate will continue to be of concern during the coming decades.
Hypothesis 2b [which is the IPCC perspective] is although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and are dominated by the emissions into the atmosphere of greenhouse gases, the most important of which is CO2. The adverse impact of these gases on regional and global climate constitutes the primary climate issue for the coming decades.
We further wrote that
We therefore conclude that hypothesis 2a is better supported than hypothesis 2b, which is a policy that focuses on modulating carbon emissions. Hypothesis 2b as a framework to mitigate climate change will neglect the diversity of other, important first- order human climate forcings that also can have adverse effects on the climate system. We urge that these other climate forcings should also be considered with respect to mitigation and adaptation policies.
“In addition to greenhouse gas emissions, other first order human climate forcings are important to understanding the future behavior of Earth’s climate. These forcings are spatially heterogeneous and include the effect of aerosols on clouds and associated precipitation [e.g., Rosenfeld et al., 2008], the influence of aerosol deposition (e.g., black carbon (soot) [Flanner et al. 2007] and reactive nitrogen
[Galloway et al., 2004]), and the role of changes in land use/land cover [e.g., Takata et al., 2009]. Among their effects is their role in altering atmospheric and ocean circulation features away from what they would be in the natural climate system [NRC, 2005]. As with CO2, the lengths of time that they affect the climate are estimated to be on multidecadal time scales and longer.”
UCAR has a press release of an upcoming article to appear in Science Express that further supports hypothesis 2a and refutes hypothesis 2b.
The UCAR press release is titled
Excerpts from the news release read
“The monsoon is one of the most powerful atmospheric circulation systems on the planet, and it happens to form right over a heavily polluted region,” says NCAR scientist William Randel, the lead author. “As a result, the monsoon provides a pathway for transporting pollutants up to the stratosphere.”
“Once in the stratosphere, the pollutants circulate around the globe for several years. Some eventually descend back into the lower atmosphere, while others break apart.”
“The study suggests that the impact of Asian pollutants on the stratosphere may increase in coming decades because of the growing industrial activity in China and other rapidly developing nations. In addition, climate change could alter the Asian monsoon, although it remains uncertain whether the result would be to strengthen or weaken vertical movements of air that transport pollutants into the stratosphere.”
Of course, these aerosols are part of climate change, but otherwise this article is quite correct in identifying yet another important human climate forcing beyond CO2 as well as emphasizing the importance of regional atmospheric circulations in the assessment of climate change. Clearly a global average surface temperature trend tells us nothing useful with respect to this climate effect.