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?
AIP Conf. Proc. 1527, pp. 579-582; doi:http://dx.doi.org/10.1063/1.4803337 (4 pages)
Abstract:
Clean-air policies in developing countries have resulted in reduced levels of anthropogenic atmospheric aerosol pollution. Reductions in aerosol pollution is thought to result in a reduction in haze and cloud layers, leading to an increase in the amount of solar radiation reaching the surface, and ultimately, an increase in surface temperatures. There have been many studies illustrating coherent relationships between surface solar radiation and temperature however, a direct link between aerosol emissions, concentrations, and surface radiation has not been demonstrated to date. Here, we illustrate a coherence between the trends of reducing anthropogenic aerosol emissions and concentrations, at the interface between the North-East Atlantic and western-Europe, leading to a staggering increase in surface solar radiation of the order of ∼20% over the last decade.
h/t to Sunshine Hours
It seems like a possible case of Occam’s Razor in action – the simplest explanation is the most likely.
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I have a problem with this proposal. This appears to be an urban issue and not a global issue.
If global brightening is fact, what now, do we wait until it gets too cold, then light up anything that’s coal fired?
If so, China can continue saving the planet for us. Ö¿Ö
What is totally unconvincing about the pollution-driven dimming/brightening explanation of world-wide temperature swings in the latter half of the 20th century is that the Southern Hemisphere, where such pollution was minimal, swung quite coherently and in-phase with the NH, where the pollution was the greatest. Since, there is very little exchange of air masses between the hemispheres, something quite different is manifestly at work.
@1sky1 . . you overlook the enormous amount of forest and savanah that is burned every year in sub-saharan Africa which I understand is similar in South America too. It generates a huge amount of soot and other particulates and goes on from late June to the end of October.
There are no good datasets of solar insolation (sunlight reaching the ground) pertaining to the 1950’s or 60’s. Actually, good solar insolation data are hard to come by.
Back in the 1970’s, the days of Jimmy Carter and the Arab oil embargoes, there was a government push toward solar power— just as now, but then of course we didn’t have global-warming activists/profiteers. Then the emphasis was on just coming up with energy so as to not be dependent upon the Arabs. (Would that we had succeeded!)
So records on solar insolation everywhere were of interest, as the records could be used to determine whether a given place was too habitually cloudy for solar power (nowadays it’s put in everywhere, even though it’s feasible nowhere).
Well, the database consisted of bolometric measurements— you measure the temperature of a blackened surface that is exposed to the sky. It was found that the autorities had neglected calibration of the bolometers for decades (they’re not particularly easy to calibrate). And so there was a downward drift in the measurements of insolation due to such things as the black becoming not so black. Or the glass cover suffering a thin-film buildup.
So no, you can’t trust one of these warmer profiteer “scientists” to come up with anything but another publish-or-perish article from time to time.
Keitho;
You apparently are unacquanted with those places. In Sub-Saharan Africa June to October is the peak of the monsoon season and there is no widespread burning going on. Dust raised by Harmattan winds during the dry season is the chief source of particulates in that region. Slash and burn agriculture is not a serious issue there. There has been much land-clearing by fire In the Amazon basin in recent decades; however, carbon soot does not stay long in the atmosphere there. In any event, it cannot explain both hemispheres being in sync in their recent temperature swings.
1sky1 . . sorry , the dry season in sub Saharan Africa runs from the end of May at the latest to the end of October. I have watched weeks of nothing but smoke in the air from Mozambique and right across Zimbabwe into northern Botswana. Bush fires are a real thing and they dim the sun bigtime.
Keitho:
Sorry, but sub-Saharan Africa is a geographic term that refers properly to the Sahel and the equatorial forest zone along the Gulf of Guinea. You are talking about SE Africa. Nevertheless, your basic argument doesn’t hold, because slash-and-burn agriculture there is not a post-WWII activity; it has been going on for centuries. The inter-hemispheric coherence of the recent multidecadal temperature swings remains unexplained by bush fires that you’ve seen dimming the sun. If anything they should produce dry-season cooling in SE Africa.