New paper finds global dimming & brightening were due to natural changes in cloud cover, not man-made aerosols
A new paper published in the Journal of Geophysical Research Atmospheres find that “changes in cloud cover rather than anthropogenic aerosols emissions played the major role in determining solar dimming and brightening during the last half century and that there are reasons to suppose that these findings may have wider relevance.” The wider relevance is that the well-known global dimming of the 1970’s ice age scare, followed by the global brightening to the end of the 20th century were largely if not entirely due to natural changes in cloud cover, potentially mediated by the solar/cosmic ray/cloud amplification mechanism of climate change. Further, since this study and another recent study on volcanic aerosols greatly diminish the assumed aerosol forcing on climate [cooling], this means that the role of man-made CO2 forcing on climate must also be reduced by the same amount to maintain so-called “radiative balance.” Thus, the climate sensitivity to CO2 must be much less than previously believed. The rate of warming increased by a factor of 3.8 from 1992 to 2002 corresponding to the period of “global brightening,” and was followed by global cooling and a “pause” or possible “dimming” of solar surface radiation. Related: Three new studies demonstrate climate sensitivity to CO2 is very low The cause of solar dimming and brightening at the Earth’s surface during the last half century: Evidence from measurements of sunshine durationGerald Stanhill*, Ori Achiman, Rafael Rosa and Shabtai CohenAnalysis of the Angstrom-Prescott relationship between normalized values of global radiation and sunshine duration measured during the last 50 years made at five sites with a wide range of climate and aerosol emissions showed few significant differences in atmospheric transmissivity under clear or cloud-covered skies between years when global dimming occurred and years when global brightening was measured, nor in most cases were there any significant changes in the parameters or in their relationships to annual rates of fossil fuel combustion in the surrounding 1° cells. It is concluded that at the sites studied changes in cloud cover rather than anthropogenic aerosols emissions played the major role in determining solar dimming and brightening during the last half century and that there are reasons to suppose that these findings may have wider relevance.
— gReader Pro