The 21st Century slow-down of climate warming appears related to the Maunder Minimum (low sunspot activity).

Solar scientists have identified that a slow-down in global warming came on with the start of the 21st Century. At that time, the sun entered a period of low sunspot activity. In 2007-8, scientists began to study this low sunspot activity in the context of a prior record of low sunspot activity, dubbed the “Maunder Minimum,’ which occurred synonymously with a “mini-ice-age” during the Medieval period in history.

The current slow-down of warming at the beginning of the 21st Century has been attributed to the climate-cooling effect of a Maunder Minimum which commenced at that time.

The new light shed on the climate change debate, by study of the Maunder Minimum, has been discussed by authors Beckman and Mahoney, who summarized the scope of their research as follows:

Abstract: We discuss how, in the 1970’s, Eddy took clues from the historical researches of Spörer and Maunder in the 19th century to draw attention to the virtual absence of sunspot activity between 1645 and 1715. This “Maunder Minimum” is not only of interest to solar physicists in the context of the theory of solar magnetic activity, and to stellar astrophysicists working on the properties of cool stars, but may also be a vital clue to the influence of the variability of the Sun’s power output on terrestrial climate. Without the availability of the historical documentary records the long-term variability of the Sun implied by the Maunder Minimum would not have come to light, and the consequent advances in stellar physics and in palaeoclimatology would not have been possible.

1. Introduction: the Solar Cycle and its Variation

We are all familiar with the 11-year sunspot cycle. One familiar factor is the effect of solar activity on short-wave radio communications. During sunspot maximum high-energy protons and alpha particles from the Sun affect the ionosphere, reducing its effectivity as a mirror from which short radio waves are reflected round the world, disrupting transmissions for days at a time.

The association with the presence of large numbers of dark spots on the solar disc is widely known, and well understood, and it is also clear that such maxima repeat every 10 or 11 years, with minima between them.

More specialized is the knowledge that this cycle was discovered only some 150 years ago by Schwabe (1843), and put on a firm observational basis during the last century by Wolf (1856, and subsequent papers, summarized in Waldmeier 1961).

Even more specialized, at least until the need to understand climate change pushed it to the fore in the 1980’s, was the belief that the present solar cycle might not be a permanent feature of solar behaviour. The key impulse here was the work of Eddy in the late 1970’s, focused especially on the historical period between 1645 and 1715, for which there is evidence that sunspot activity was strongly suppressed or virtually absent.

If this is accepted as true, it has strong implications for our ideas of how magnetic fields in stars are produced.

Of more impact, it might go some of the way, even all of the way, to explaining the observed pattern of global warming of the Earth in the last decades of the 20th century. This makes the “discovery” of more than academic interest.

The authors of this paper discuss the validity of research of preceding scientists in times when scientists were few, and also identify the scope and newness of adding the solar causation to the global warming debate:

One should be wary of jumping to conclusions about the role of greenhouse gases in our atmosphere in procuring a generalized warming of the Earth, given the great complexity of physical processes inherent in the reaction of the atmosphere-ocean system to a change in atmospheric transparency, knowing that such a change is in fact occurring as a result of the emission of gases in industry and transport.

To this area of doubt the advocates of solar global warming have been able to add their element of confusion.

Maybe we are experiencing a steady rise in the solar constant, accompanying a similar rise in solar magnetic variability, and maybe the greenhouse effect is not the main agent, or even a cause, of global warming.

The complete paper may be found here.

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