As noted by Dr. Roy Spencer,
"The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling."Changes in cloud cover may occur due to solar amplification mechanisms such as via solar control of cosmic ray cloud nucleation and solar modulation of ocean and atmospheric oscillations, or may occur as a negative feedback to surface warming and increased evaporation.
| 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. |
The cause of solar dimming and brightening at the Earth's surface during the last half century: evidence from measurements of sunshine duration.
Gerald Stanhill et al
Analysis 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 change 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.
Related:
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How climate models dismiss the role of the Sun in climate change [Part 4]
Found another paper with the same conclusions.
ReplyDeleteINTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. (2008) DOI: 10.1002/joc.1735
Global dimming and global brightening – an analysis of surface radiation and cloud cover data in northern Europe Camilla W. Stjern,a* Jon Egill Kristj ´ ansson ´ a and Aksel Walløe Hansenb a Department of Geosciences, University of Oslo, Blindern, N-0315 Oslo, Norway b Department of Geophysics, Niels Bohr Institute, University of Copenhagen, Denmark
ABSTRACT: In the present study, surface solar radiation data from 11 stations in northwestern Europe and the European Arctic are presented in the context of the ongoing discussion on global dimming and global brightening. The surface solar radiation records are compared to records of cloud cover, and to qualitative information on aerosol concentrations and atmospheric circulation patterns, in order to explain the temporal variations. Through simple statistical analyses, we examine annual trends as well as trends for individual months, and compare the results between the stations. Comparisons are also made between different time periods within the records.
We find that surface solar radiation changes in the region considered, even at the remote arctic stations, correspond well with trends found in global studies, with a significant decrease from the 1950s to the 1980s, followed by a slight increase in recent years. At stations that stand out from the general pattern, the deviations can be explained by variations in cloud cover in most cases.
There has been a general tendency to attribute the majority of the observed surface solar radiation trends to aerosol changes caused by changes in anthropogenic emissions. This study stresses the importance of the contribution of clouds and the atmospheric circulation to global dimming and global brightening.
2008 Royal Meteorological Society Received 21 December 2006; Revised 18 January 2008; Accepted 20 May 2008
Thanks for this!
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