People who suggest there is some kind of covert geoengineering program going on (the term "geoengineering" is often used to refer to a variant of the "chemtrails" theory), often point to global dimming (a reduction of the amount of sunlight hitting the earth's surface) as evidence of this. Here's an example:
http://www.geoengineeringwatch.org/welcome2page/10-bullet-points-regarding-geoengineering/
The most comprehensive overview of the Subject is by Wild, 2012, and his findings are confirmed by other studies. I've highlighted the important parts below.
Martin Wild, 2012, Institute for Atmospheric and Climate Science, Zurich, Switzerland. Published in the American Meteorological Society:
Enlightening Global Dimming and Brightening
http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-11-00074.1
One interesting thing there is "Note that “global” thereby originally referred to “global radiation,” a synonym for SSR, rather than to a globalscale dimension of the phenomenon " - meaning "global dimming" did not actually mean the entire globe is dimming, even back in the 1980s. It was just the "global radiation" (i.e. the full spectrum) at particular locations.
Other recent studies have similar results.
http://adsabs.harvard.edu/abs/2013EGUGA..15.2579W
2013: Wang
2012, Hatzianastassiou, et al., Features and causes of recent surface solar radiation dimming and brightening patterns:
2013, O'Dowd, et al.
Cleaner air: Brightening the pollution perspective?
http://www.geoengineeringwatch.org/welcome2page/10-bullet-points-regarding-geoengineering/
The problem with the above assertion is that it's wrong, it's basically an interpretation of data that is 20 years out of date. "Global Dimming" was a real thing, from around 1950 to the late 1980s. But it has since been replaced in most places (including North America) by "Global Brightening", generally because of the reduction in pollution brought about by the clean air acts around the world.5. SAG [Stratospheric Aerosol Geoengineering] and SRM [Solar Radiation Management] are causing “global dimming” on a scale that can hardly be comprehended. Current figures are averaging in the 20% range globally, but in some areas, like Russia, the total amount of sun that now reaches the ground is some 30% less than only a few decades previous. This reduction of sunlight further amplifies the currently occurring global droughts. Sunlight is a major component of evaporation
The most comprehensive overview of the Subject is by Wild, 2012, and his findings are confirmed by other studies. I've highlighted the important parts below.
Martin Wild, 2012, Institute for Atmospheric and Climate Science, Zurich, Switzerland. Published in the American Meteorological Society:
Enlightening Global Dimming and Brightening
http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-11-00074.1
WHAT OBSERVATIONS TELL. Early studies carried out in the 1990s pointed to a remarkable decline of SSR [Surface Solar Radiation] at selected observation stations between the 1950s and the 1980s. These pioneering studies were based on sites in Europe (Ohmura and Lang 1989), the Baltic (Russak 1990), the South Pole (Dutton et al. 1991), different regions globally (Stanhill and Moreshet 1992), Germany (Liepert et al. 1994), and the former Soviet Union (Abakumova et al. 1996). By now a comprehensive literature exists that confirms declines of SSR during this period in many places around the globe (e.g., Gilgen et al. 1998; Stanhill and Cohen 2001 and references therein; Liepert 2002; Ohmura 2009; Wild 2009 and references therein). This phenomenon is popularly described as “global dimming” (Stanhill and Cohen 2001) (see Fig. 1 left, for a schematic illustration). Note that “global” thereby originally referred to “global radiation,” a synonym for SSR, rather than to a globalscale dimension of the phenomenon
Qualitative SSR tendencies in those parts of the globe with best availability of long-term observations are compiled in Fig. 2. The left column illustrates the overall decline of SSR measured at sites in America, Europe, China, and Japan between the 1950s and 1980s (the “dimming phase”). Magnitudes of the tendencies (in W m−2 per decade) as prevalent in the literature are also added in Fig. 2 for illustration, but note that considerable spread exists in these regional estimates with undefined uncertainty ranges.
More recent studies using SSR records updated to the year 2000 found, however, a trend reversal and partial recovery at many of the sites since the 1980s. The term “brightening” was thereby coined to emphasize that the decline in SSR and associated global dimming no longer continued after the 1980s (Wild et al. 2005) (Fig. 1, right). Particularly in industrialized areas, the majority of the sites show some recovery from prior dimming, or at least a leveling off, between the 1980s and 2000 (the “brightening phase”) (Fig. 2, middle column). The brightening is somewhat less coherent than the preceding dimming, with trend reversals at widespread locations but still some regions with continued decrease (e.g., India; Kumari and Goswami 2010). Note that observed brightening has generally not fully compensated for prior dimming, so that insolation levels at the turn of the millennium were typically still below those in the 1950s. Literature estimates for the overall SSR decline during dimming range from 3 to 9 W m−2, and from 1 to 4 W m−2 for the partial recovery during subsequent brightening (Stanhill and Moreshet 1992; Liepert et al. 1994; Abakumova et al. 1996; Gilgen et al. 1998; Stanhill and Cohen 2001; Alpert et al. 2005; Kvalevag and Myhre 2007; Kim and Ramanathan 2008; Wild 2009) (Fig. 1), with more likely values closer to the lower bound because of possible inherent urbanization effects (Alpert et al. 2005; Kvalevag and Myhre 2007) (see below).
The latest updates on developments beyond the year 2000 show mixed tendencies (Fig. 2, right column). Overall, observed brightening is less distinct after 2000 compared to the 1990s at many sites. Brightening continues beyond 2000 at sites in Europe and the United States but levels off at Japanese sites, and there are some indications for a renewed dimming in China after a phase of stabilization during the 1990s, while dimming persists throughout in India (Wild et al. 2009).
On the other hand, the longest observational records, which go back to the 1920s and 1930s at a few sites in Europe, further indicate some brightening tendencies during the first half of the twentieth century, known as “early brightening” (Ohmura 2009; Wild 2009).
Fig. 1. Schematic representation of “dimming” and “brightening” periods over land surfaces. (left) During dimming (1950s–80s) the decline in surface solar radiation (SSR) may have outweighed increasing atmospheric downwelling thermal radiation (LWdown) from enhanced greenhouse gases and effectively counteracted global warming, causing only little increase in surface thermal emission (LWup). The resulting reduction in radiative energy at Earth’s surface may have attenuated evaporation and its energy equivalent, the latent heat flux (LH), leading to a slowdown of the water cycle. (right) With the transition from dimming to brightening (1980s–2000s), the enhanced greenhouse effect has no longer been masked, causing more rapid warming, stronger evaporation/LH, and an intensification of the water cycle. Values denote best estimates of overall changes in surface energy fluxes over both periods in W/m2 (ranges of literature estimates for SSR dimming/brightening in parentheses). Positive (negative) numbers, shown in red (blue), denote increasing (decreasing) magnitudes of the energy fluxes in the direction indicated by the arrows. Changes in ground heat flux (GH) and sensible heat flux (SH) are considered small compared to the above mentioned flux changes.
One interesting thing there is "Note that “global” thereby originally referred to “global radiation,” a synonym for SSR, rather than to a globalscale dimension of the phenomenon " - meaning "global dimming" did not actually mean the entire globe is dimming, even back in the 1980s. It was just the "global radiation" (i.e. the full spectrum) at particular locations.
Other recent studies have similar results.
http://adsabs.harvard.edu/abs/2013EGUGA..15.2579W
2013: Wang
http://adsabs.harvard.edu/abs/2012EGUGA..1413344HSurface 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.
2012, Hatzianastassiou, et al., Features and causes of recent surface solar radiation dimming and brightening patterns:
http://proceedings.aip.org/resource/2/apcpcs/1527/1/579_1?isAuthorized=nosurface measurements have indicated a widespread decrease of surface solar radiation (SSR) from the 1950s to the 1980s, described as global dimming, followed by a period with either no more decrease or even an increase at various locations worldwide till the end of 1990s, namely a global brightening.
...
An inter-hemispherical difference is revealed up to 2007, consisting in a clear dimming in the South Hemisphere (SH), against a no clear dimming/brightening signal in North Hemisphere (NH), under all-sky conditions.
2013, O'Dowd, et al.
Cleaner air: Brightening the pollution perspective?
Update: Martin Wild gave a presentation on the topic at the American Geophysical Union (AGU) Fall Meeting in San FranciscoHere, 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 [about] 20% over the last decade.
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I only watched and did not listen to what he said . Hard to understand with accent . Looked quite the same in FL as well . Pretty sad the skies look like crap . Sure were pretty heavy contrail s ? I meant to use the Shakespeare quote
