The Solar Control of Climate: A Review
by David Archibald
28 August 2024
This review was prepared for a Zoom interview on the Sun’s role in climate. Some say carbon dioxide is the controlling variable in climate. That notion is discredited, most recently by a study on variation in the Earth’s albedo. As the following figure from that study shows, all of the atmosphere’s temperature rise this century mirrors the reduction in albedo with no room for a contribution from carbon dioxide:
This is consistent with the logarithmic heating effect of carbon dioxide. Half of the warming from atmospheric carbon dioxide comes from the first 20 ppm and then rapidly drops away from there. Carbon dioxide is tuckered out as a greenhouse gas:
From the current 423 ppm, each 100 ppm increase results in a temperature rise of only 0.1°C. The atmosphere will only get to about 600 ppm before we run out of rocks we can dig up and burn. So the warming effect from carbon dioxide is only good for another 0.2°C. There is no human on our planet sensitive enough to feel a 0.2°C difference in temperature. And this story doesn’t have a happy ending. There is 50 times as much carbon dioxide in the oceans than in the atmosphere, so the 800-year turnover of the oceans will take 98% of the carbon dioxide humans have added to the atmosphere down to the Davy Deep and we won’t see it again. A couple of hundred years from now our descendants will be lamenting the annual decline in crop yields due to falling carbon dioxide levels.
There is plenty of evidence that solar activity controls climate. The first observation of the correlation of solar activity and climate was in 432 BC by the Greek philosopher Meton, who noted the correlation between sunspots and rainfall amount. Books have been written about it for the last four hundred years. One of the better ones is Hoyt and Schatten’s The Role of the Sun in Climate Change, from late last century. That book starts with this figure of the correlation between the frequency of Indian cyclones and sunspot cycles in the mid-19th century:
And describes the correlation between solar cycles and the number of hares in the Canadian wilderness:
A 1993 study by Sinclair and his associates at the University of British Columbia has new approach to estimating mammal populations. The lynx population depends on the rabbit population. Rabbits feed on the shoots of tree saplings. As rabbit populations expand, they eat more and more shoots and eventually consume their entire food supply. Most rabbits now starve, and numerous predators eat the rest. The rabbit and its dependent lynx populations both collapse, allowing the tree shoots to resume growing, starting the cycle anew. Sinclair and his associates use this model to trace rabbit populations in the Arctic during the last two centuries. They find that as rabbits nibble off the ends of the tree shoots, they leave scars that are preserved in the tree rings.
By counting the density of these scars, scientists can deduce the population of shoot-eating snowshoe hares. Since 1750 the hare population closely parallels the sunspot cycle, especially when the sunspot cycle is strong. For the weaker sunspot cycles, the snowshoe hare cycle becomes closer to 10 years and diverges from the sunspot cycle. When high activity returns, the two cycles mesh together again. The linkage may derive from an alteration in weather. High solar activity may produce somewhat warmer and wetter weather, which is conductive to tree growth. Perhaps, on these occasions, this extra stimulation is sufficient to control the hare population through tree growth, locking solar activity, hare populations, and lynx populations in phase. Of course, more study is required.
Another good correlation of solar activity and climate is shown by the Dye 3 ice core Be10 record:
The cold periods of the last 600 years were caused by episodes of weak solar activity, with a weak solar magnetic flux, allowing more galactic cosmic rays to impinge on the earth’s atmosphere. These in turn provided nucleation sites in the lower atmosphere for clouds to form, increasing the Earth’s albedo and in turn reflecting more sunlight back into space. The pleasant warming of the 20th century was due to stronger solar activity. In fact, solar activity was stronger in the second half of the 20th century than it had been for the previous eleven thousand years:
That’s enough of stating the obvious — that the Sun controls climate. With respect to using solar activity to predict climate, Butler and Johnson in their 1996 paper found a good correlation between solar cycle length and temperature over the following solar in data from the Armagh weather station in Northern Ireland:
Using the relationship demonstrated by that figure, Solar Cycle 24 should have been 2.4°C colder than Solar Cycle 23. It wasn’t. But sometimes solar-climate relationships break down and come back again. A good example of that is from Lake Victoria in Africa. A century ago it was realised that there is a correlation between the solar cycle and the lake level. That ended in 1928 and resumed forty years later in 1968:
A similar thing is seen in the correlation between sea level rise and solar cycles:
Sea level rise was chaotic up to the end of the Little Ice Age then had 40 good years of correlation from 1948 to 1987.
The proximate cause of the 40 year hiatus in the Lake Victoria lake level – solar cycle relationship may have been the start of the Modern Warm Period. The aa Index, a geomagnetic index that indicates solar activity, goes back to 1868 and shows three periods of activity:
These are the Little Ice Age, the Modern Warm Period and the New Cold Period. We can be certain of the boundaries of the Modern Warm Period because when we plot up the data from that graph as a cumulative graph, they are marked by major changes in trend:
The aa Index data, properly interpreted, indicates cooling from here. That interpretation is supported by the Ap Index which broke down through its activity floor of the Modern Warm Period in 2008:
That is long term cooling. The near term prediction out to mid-century is a Goldilocks result – not too hot and not too cold. How we know is that in 2009 I was approached by Ed Fix, a former B-52 pilot living in Ohio. The solar cycle record reminded Ed of the ideal spring relationship in engineering. So he downloaded the planetary ephemeris data from a NASA website and made up a model. Ed had approached other people before me but I was the first to take him seriously — because the hindcast match was so good. His first paper on this was published in 2011 in the book Evidence-Based Climate Science, edited by Don Easterbrook. We collaborated on a second paper in a second edition in 2016. From the second paper, this figure shows what is going to happen from here:
Solar Cycle 25 is now stronger than Solar Cycle 24 was. The model output indicates that Solar Cycle 26 will be stronger again, perhaps an amplitude similar to Solar Cycle 20. So solar activity won’t be flatlining and extreme cold is unlikely. That said, Solar Cycle 20 includes the 1970s Cooling Period. And short periods of extreme cold can come out of the blue. For example, in the winter of 1740, Ireland had seven weeks of very cold weather which caused the death of 20% of its population. The Irish potato famine occurred 105 years later.
Ed’s work shows that while Jupiter and Saturn have little individual effect on the Sun, their combined effect is synergistic. Neptune and Uranus either add to that effect or detract from it. A further refinement of Ed’s model is possible. The following figure shows that the Northern and Southern hemispheres of the Sun have different solar cycles with energy conserved separately in each hemisphere. In Solar Cycle 24, the peak of the cycle in the southern hemisphere was three years later than in the northern hemisphere:
The fact that the peaks of three solar cycles line up for each hemisphere means that there is some consistent, mechanistic effect that operates for decades at a time. The most likely explanation for this phenomenon is that the gas planets orbit the Sun at an angle to the plane of the Solar System. Ed’s model is currently a 2D model; a 3D version might have more predictive power.
By the way, climate will look after itself and nobody is going to die from it being too hot or too cold. There are far more important things to worry about. That said, it would be best to keep an open mind and follow up on things that suggest the potential for excursions from the Goldilocks climate outlook. A case in point is the Finnish tree ring study published in 2008 on the Scots pine timberline in Finland, from 1500 to 2008. One of the tentative forecasts from that study is of a cold period starting from 2025 which will be as long as deep as any in the last 500 years:
David Archibald is the author of American Gripen: The Solution to the F-35 Nightmare and The Anticancer Garden in Australia.