Pollution controls have contributed to a more transparent atmosphere, thus allowing for “…a staggering increase in surface solar radiation of the order of ∼20% over the last decade.”

A new paper (O’Dowd et al.) from the National University of Ireland presented this summer at the 19th International Conference on Nucleation and Atmospheric Aerosols suggests that clean air laws put in place in the 1970’s and 80’s have resulted in an increase in sunlight impacting the surface of the Earth, and thus have increased surface temperatures as a result. In one fell swoop, this can explain why surface temperature dipped in the 1970’s, prompting fears of an ice age, followed by concerns of global warming as the air got cleaner after pollution laws and controls were put in place.

WUWT covered a similar effort (Wild 2009) here and paper here (PDF 1.4 mb) which showed the issue but fell short of showing a provable causation for temperature.

Now with this new effort by O’Dowd et al., it seems quite likely that cleaner air is in fact allowing in more solar radiation to the surface, and thus increasing surface temperatures by that increase of insolation.

Wild 2012, was a follow up, and figure 1 above is from that paper.

Martin Wild, 2012, Institute for Atmospheric and Climate Science, Zurich, Switzerland. Published in BAMS: Enlightening Global Dimming and Brightening

http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-11-00074.1 (open PDF)

Now with O’Dowd et al. and their findings, this “global brightening” as a climate driver is looking much more plausible.

The authors write in the new O’Dowd paper:

This study has demonstrated for the first time, using in-situ PM measurements, that reducing aerosol pollution is driving the Insolation Brightening phenomenon and that the trends in aerosol pollution, particularly for sulphate aerosol, is directly linked to anthropogenic emissions. Ultimately, the analysis demonstrates that clean air policies in developed regions such as Europe are driving brightening of the atmosphere and increasing the amount of global radiation reaching the Earth’s surface. The actual impact of cleaner air and insolation brightening on temperature remains to be elucidated.

And offer this graph:

This is inline with Hatzianastassiou et al., 2012, Features and causes of recent surface solar radiation dimming and brightening patterns:

Surface incident solar radiation has been widely observed since the late 1950s. Such observations have suggested a widespread decrease between the 1950s and 1980s (“global dimming”) and a reverse brightening afterward.

http://adsabs.harvard.edu/abs/2012EGUGA..1413344H

The new O’Dowd paper:

Cleaner air: Brightening the pollution perspective?