Changes in solar output, not humanity’s carbon dioxide emissions, is likely the primary driver of climate change over at least the past few centuries.
Scientists have long observed a noticeable relationship between solar activity, as indicated by sunspot numbers, and so-called “global temperatures” for centuries. It was in 1613 when Galileo Galilei, the father of modern astronomy, used the newly invented telescope to begin recording darker areas, some far larger than the Earth, on the surface of the Sun. It caused a social and religious uproar because everything beyond the Moon was supposed to be pristine and unblemished despite the fact that there are records from Ancient Greece and China from centuries before Christ of observations of these dark areas.
Some people argued that the dark areas were moons or planets in front of our home star. But Galileo was right—they are actually a characteristic of the Sun itself, a phenomenon we now call sunspots.
Today, we know that sunspots are areas of the sun's atmosphere which are up to 3,000 degrees Kelvin cooler than the surrounding photosphere, making them appear much darker. They are caused when the Sun's magnetic field breaks through the surface.
The number of sunspots rises and falls in a regular 11-year cycle. This coincides with a change in the amount of radiation emitted by the Sun. Even though sunspots are much cooler than the rest of the photosphere, the Sun is more active when the number of sunspots is also at a maximum.
What scientists observed was that, when there were many sunspots, the Earth was warmer. When there were fewer spots, it was colder. Why this was the case, no one knew. After all, as I pointed out in my article from two weeks ago:
“The Total Solar Irradiance, the amount of solar energy reaching the top of Earth’s atmosphere, only varies by about 0.1% over the course of the familiar 11-year sunspot cycle. While the variations can be greater for longer cycles, for example, the 200-year solar cycle, they are still insufficient to account for the observed warming, at least via direct solar insolation changes.”
So, for changes in the Sun’s output to be a significant driver of the climate change we have seen over the past century and before, there would have to be a natural factor amplifying these changes.
Until the 1990s, no plausible explanation for this problem existed, so one could argue that the United Nations Intergovernmental Panel on Climate Change (IPCC) was probably justified to ignore sunspots in predicting future climate. But, in 1991, two researchers from the Danish Meteorological Institute, E. Friis-Christensen and K. Lassen, published a new theory in “Length of the Solar Cycle: An Indicator of Solar Activity Closely Associated with Climate.” It was not the answer to the amplification issue, but it was a step forward in recognizing that the Sun plays a more significant role than previously thought. By 1997 scientists started to home in on the answer when Friis-Christensen and Henrik Svensmark, also of the Danish Meteorological Institute, published the paper, “Variation of Cosmic Ray Flux and Global Cloud coverage – A Missing Link in Solar-Climate Relationships.”
As I described in last week’s article, galactic cosmic rays (GCRs) are high-energy (and high speed, nearly the speed of light) atomic nuclei or other particles traveling through space that originate in supernovas in deep space, eventually flooding into our solar system. When they enter the Earth’s atmosphere, they appear to affect climate (note: lower energy cosmic rays originate in the Sun and the variability of solar cosmic rays probably affects climate as well).
The IPCC was still perhaps right to not accept these untested new ideas. However, by 2000 the theory was evaluated through experiments and what is now known as the Svensmark or Cosmic Theory appears to provide the missing amplifier that accounts for the observed correlation between solar activity and Earth’s climate.
Here is how it works.
To reach us here on Earth, GCRs must pass through, and is diverted by, the Sun’s magnetic field, which varies in strength as solar activity changes as indicated by the changing sunspot numbers. When the field is strong during solar maximum, less GCRs penetrate into the solar system than when the field is weak (note: Cosmic Ray Flux (CRF) is also be affected by the Earth’s magnetic field and that too may be influenced by the strength of the magnetic field of the Sun, but that is beyond the scope of this article).
As GCRs enter the Earth’s atmosphere, they help form particles called aerosols in the lower atmosphere which may grow to cloud condensation nuclei. These are particles around which water can form to create droplets of water, a million of which are needed to make a moderate-sized raindrop. While the original droplets are microscopic in size, they are visible as clouds which act like a screen in a greenhouse controlling the amount of sunlight that can penetrate the atmosphere to heat the Earth’s surface.
So, when the Sun is in a strong phase, with a stronger magnetic field, less GCRs enter the Earth’s atmosphere and we have less clouds. This then amplifies the warming that is directly caused by a more active Sun.
Once again, the sequence of events is:
- a strong Sun causes slight warming on the Earth due to increased solar energy input to our planet.
- a strong Sun also causes a stronger solar magnetic field
- this field reduces the amount of GCRs that can enter the solar system and so Earth’s atmosphere
- so less clouds form, amplifying the initial warming by the Sun.
The reverse is also believed to be true:
- a weaker Sun produces less warming on Earth due to decreased solar energy input to our planet.
- a weaker Sun also causes a weaker solar magnetic field
- this weakened field allows more GCRs to enter the solar system and so Earth’s atmosphere • so more clouds form, further reducing the initial reduced warming of the Sun.
Now here is where the work of Professor Nir Shaviv of the Hebrew University of Jerusalem and Professor Jan Veizer, the Distinguished University Professor (emeritus) of Earth Sciences at the University of Ottawa, that I discussed in the two previous parts of this series, comes in.
There was initially, and to some extent still is, disagreement in the climate science community (see The Cloud Mystery documentary) as to whether cosmic ray flux (CRF) really did cause significant changes in climate as Svensmark hypothesized.
But when the work of Shaviv and Veizer came out, it gave independent support to the idea that CRF was indeed a significant driver of climate, at least on geologic timescales. It was independent since it is not solar activity changing the cosmic rays affecting the climate over decadal time scales, as Svensmark proposed. Instead, Shaviv and Veizer’s work was over hundred million-year timescales in which cosmic rays clearly drove climate due to the frequency and proximity of supernovae. This then lent significant support to Svensmark’s theory, important parts of which were bolstered in experiments that Svensmark carried out, and also in the CLOUD experiment at the European Organization for Nuclear Research (CERN), an intergovernmental organization that operates the largest particle physics laboratory in the world in Switzerland.
Science writer Nigel Calder reported that the experiments that could prove Svensmark’s theory were delayed for a strange reason:
“The Director General of CERN stirred controversy last month, by saying that the CLOUD team’s report should be politically correct about climate change. The implication was that they should on no account endorse the Danish heresy – Henrik Svensmark’s hypothesis that most of the global warming of the 20th Century can be explained by the reduction in cosmic rays due to livelier solar activity, resulting in less low cloud cover and warmer surface temperatures.”
In the years following the work by Svensmark, Shaviv and Veizer, there has been an intense campaign aimed at discrediting the variable Sun-GCR-cloud cover idea, with some researchers seeming to show that important elements of it may be wrong. After all, if the Svensmark theory is right, as increasingly seems to be the case, then much of the raison d’etre for the multi-trillion-dollar drive to reduce carbon dioxide emissions falls apart.
At the end of The Cloud Mystery documentary Eugene Parker, Professor Emeritus in Physics Astronomy and Astrophysics at the University of Chicago said:
“This has a new dimension now that global warming is a political issue. Things become politically incorrect and, in the United States at least, we have cases of good solid research on global warming being refused for publication because somebody has made up his mind that that isn’t the way it is, and you can’t publish. I think this is not only unfortunate for the author, it is unfortunate for the country and the world as a whole because this is a problem we had better get straight so we know what to do.”
The “cosmoclimatology” work of Svensmark, Veizer, Shaviv et al is real world science in action and I will update readers about this again in the near future, so stayed tuned! But, in the meantime, we have a reasonably complete theory that fits temperature variations on Earth on timescales from days to decades to millennia to millions to billions of years. And there is empirical evidence for it all. How exciting!
Tom Harris is Executive Director of the Ottawa, Canada-based International Climate Science Coalition.
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