Not only fighting air pollution differs from fighting climate change (see previous post November 21st, 2014), it could imply the reverse! China has never been so concerned with air pollution (Hong Kong starts being upset as well, see SCMP January 25th 2015) and calls for actions have become even stronger since the “Apec blue”. General opinion seems to view this concern as being rather consistent with the fight against climate change and this is also what is suggested by the recent US-China climate agreement (November 12th, 2015). As we mentioned in our previous post, it is not that straightforward. In fact it may prove even worse than we thought!
There is now a growing literature on the “dimming” effect that had been observed in the period 1950s–80s: the decline in surface solar radiation due to aerosol and particles pollution may have outweighed increasing atmospheric downwelling thermal radiation from enhanced greenhouse gases and effectively counteracted global warming (see Wild, 2012). Notably, such an effect was already reported in 2005 by European scientists in Nature and is particularly well-known for particles emitted through volcanic eruptions (see the figure below).
A corollary is that too much aerosol removal generates a “brightening effect” that enhances climate change. Such an effect has been recently documented by O’Dowd et alii., 2013 that argue (they demonstrate the direct link between aerosol emissions, concentrations, and surface radiation) that the clean air policies might have resulted in higher temperatures.
Does this mean that we should not worry about pollution generated by fossil fuel since it generates both GHG and particles? It rather calls for more effort to fight climate change because IPPC predictions that do not account for the brightening effect underestimate future climate change. And it will be become worse. Consistent with the intuition, there has been a renewed dimming in China after a phase of stabilization during the 1990s (Wild, 2012). When looking at the air pollution, we can expect -and hope- that China now reduces efficiently air pollution, that will generate a significant brightening effect (note that this provides a fresh perspective on US-China agreements…) which enhances the need for GHG reduction.
In the meantime, the dimming effect is clearly ignored by economists. First, to my knowledge, they have never taken it into account explicitly. Second, they often consider that fossil fuel use directly generates climate change (see van der Ploeg et alii., 2012 for instance, or my work). It might in fact be crucial to distinguish between GHG and particles that both need to be reduced but affect climate change in opposite ways.
 South China Morning Post, “Every breath you take” January 25th 2015, Post Magazine. http://www.scmp.com/magazines/post-magazine/article/1689002/air-pollution-practical-tips-how-cope-it
 Wild, M. 2012: Enlightening Global Dimming and Brightening. Bull. Amer. Meteor. Soc., 93, 27–37 http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-11-00074.1
Meinrat O. Andreae1, Chris D. Jones & Peter M. Cox, Strong present-day aerosol cooling implies a hot future Nature 435, 1187-1190 (30 June 2005) | doi:10.1038/nature03671
 Seminar by Prof. Johnny Chan at City University of Hong Kong, January 9th, 2015, http://www.cb.cityu.edu.hk/cityseminar/past/20150109.html
 Colin O'Dowd, Darius Ceburnis, Aditya Vaishya, S. Gerard Jennings and Eoin Moran “Cleaner air: Brightening the pollution perspective?” AIP Conf. Proc. 1527, 579 (2013); http://dx.doi.org/10.1063/1.4803337
 Ayong le Kama A. and Pommeret A., 2015 « Adaptation and mitigation are not enough : turning to mitigation abroad “https://drive.google.com/file/d/0B563l-M03kqnTU9pdlI1R2dQWmc/view?usp=sharing