A forthcoming study in Geophysical Research Letters (subs. req’d) finds what countless other studies in the past decade have found — changes in the sun are not responsible for the global warming in recent decades.

In particular, the study debunks the notion that changes in cloud cover driven by cosmic rays are a major factor in climate change:

Changes in cosmic rays during a solar cycle are two orders of magnitude too small to account for the observed changes in cloud properties; consequently, we conclude that the hypothesized effect is too small to play a significant role in current climate change.

Of course, this finding merely adds to a vast body of scientific literature on this subject that makes clear the sun’s contribution to the accelerated warming of the last few decades is minimal.

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For instance, the Naval Research Laboratory and NASA reported in September that, “if anything,” the sun contributed “a very slight overall cooling in the past 25 years.” The study, “How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006,” found:

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According to this analysis, solar forcing contributed negligible long-term warming in the past 25 years and 10% of the warming in the past 100 years.

A major 2007 study concluded:

Here we show that over the past 20 years, all the trends in the Sun that could have had an influence on the Earth’s climate have been in the opposite direction to that required to explain the observed rise in global mean temperatures.

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Since the science doesn’t support their position, the most extreme science deniers, like Marc Morano, often just assert that studies which disprove their case actually prove their case.  Morano famously did just that back in December when he ran the screaming headline

Study: Half of warming due to Sun!

In fact, far from providing evidence for deniers, the study, also in Geophysical Research Letters (subs. req’d) actually provided yet more strong evidence on behalf of human-caused global warming (see Scientist: “Our conclusions were misinterpreted” by Inhofe, CO2 — but not the sun — “is significantly correlated” with temperature since 1850).  It concluded that

during the industrial period (1850-2000) solar forcing became less important and only the CO2 concentrations show a significant correlation with the temperature record.

Responding to an email I wrote asking for a response to Morano, the author, Anja Eichler, Senior Scientist at the Switzerland’s Paul Scherrer Institute, wrote:

You are totally right that our conclusions were misinterpreted

Eichler added that “uncertainties of our data” do not allow it to be used to give an exact percentage for how much solar activity was responsible for the warming in the past century.  But the studies cited above (and the ones listed below) make clear the contribution of solar activity to warming in recent decades is minimal.

The conclusions of the Eichler study are actually quite intriguing in that they underscore the key point that the deniers refuse to accept: The Earth’s temperature does not change randomly — it changes when it is driven to do so by an external forcing.

Yes, deniers — some of whom comment on this website — the Earth has had brief warming and cooling periods since 1250. But those temperature changes were not random. They were largely responses to changes in the solar radiation hitting the earth (which is itself affected by volcanoes).

Now human-caused emissions are driving climate change to dangerous levels with forcings that dwarf previous natural forcings both in speed and scale (see “Humans boosting CO2 14,000 times faster than nature, overwhelming slow negative feedbacks“).

And that’s why the time to act is now.

Related studies can be found on the excellent debunking website, Skeptical Science:

  • Ammann 2007: “Although solar and volcanic effects appear to dominate most of the slow climate variations within the past thousand years, the impacts of greenhouse gases have dominated since the second half of the last century.”
  • Foukal 2006 concludes “The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years.”
  • Usoskin 2005 conclude “during these last 30 years the solar total irradiance, solar UV irradiance and cosmic ray flux has not shown any significant secular trend, so that at least this most recent warming episode must have another source.”
  • Stott 2003 increased climate model sensitivity to solar forcing and still found “most warming over the last 50 yr is likely to have been caused by increases in greenhouse gases.”
  • Solanki 2003 concludes “the Sun has contributed less than 30% of the global warming since 1970.”
  • Lean 1999 concludes “it is unlikely that Sun-climate relationships can account for much of the warming since 1970″.
  • Waple 1999 finds “little evidence to suggest that changes in irradiance are having a large impact on the current warming trend.”
  • Frolich 1998 concludes “solar radiative output trends contributed little of the 0.2°C increase in the global mean surface temperature in the past decade.”