Climate sceptics' claims that UN climate science panel's AR5 report show the sun is causing global warming don't stack up
Alec Rawls, an occasional guest poster on the climate contrarian blog WattsUpWithThat who signed up to review the upcoming Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (as anyone can), has "leaked" a draft version of the report and declared that it "contains game-changing admission of enhanced solar forcing." This assertion was then repeated by James Delingpole at The Telegraph (with some added colorful language), and probably on many other climate contrarian blogs.
If the IPCC were to report that the sun is a significant player in the current rapid global warming, that would indeed be major news, because the body of peer-reviewed scientific literature and data clearly show that the sun has made little if any contribution to the observed global warming over the past 50+ years....
...The supposedly "game-changing admission" from the IPCC report is this:
"Many empirical relationships have been reported between GCR [galactic cosmic rays] or cosmogenic isotope archives and some aspects of the climate system...The forcing from changes in total solar irradiance alone does not seem to account for these observations, implying the existence of an amplifying mechanism such as the hypothesized GCR-cloud link."
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This statement refers to a hypothesis of Henrik Svensmark from the Danish National Space Institute, who has proposed that galactic cosmic rays (GCRs) could exert significant influence over global temperatures. The GCR hypothesis suggests that when they reach Earth, GCRs (high-energy charged particles originating from somewhere in our galaxy) are capable of "seeding" clouds; thus at times when a lot of GCRs are reaching the Earth's surface, more clouds will form. Clouds generally have a cooling effect on the Earth's temperature, because they reflect sunlight.
So the hypothesis goes like this: high solar activity means a strong solar magnetic field, which deflects more GCRs away from Earth, which means less cloud formation, which means less sunlight is reflected away from Earth, which means more warming. This GCR-caused warming would amplify the warming already being caused by increased solar activity. Conversely, cooling from decreased solar activity would hypothetically be amplified by more GCRs on Earth, more clouds, more reflected sunlight, and thus more cooling.
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