The Maunder Minimum and the Variable Sun-Earth Connection
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The Maunder Minimum and the Variable Sun-Earth Connection (Front illustration: the Sun without spots, July 27, 1954) By Willie Wei-Hock Soon and Steven H. Yaskell To Soon Gim-Chuan, Chua Chiew-See, Pham Than (Lien+Van’s mother) and Ulla and Anna In Memory of Miriam Fuchs (baba Gil’s mother)---W.H.S. In Memory of Andrew Hoff---S.H.Y. To interrupt His Yellow Plan The Sun does not allow Caprices of the Atmosphere – And even when the Snow Heaves Balls of Specks, like Vicious Boy Directly in His Eye – Does not so much as turn His Head Busy with Majesty – ‘Tis His to stimulate the Earth And magnetize the Sea - And bind Astronomy, in place, Yet Any passing by Would deem Ourselves – the busier As the Minutest Bee That rides – emits a Thunder – A Bomb – to justify Emily Dickinson (poem 224. c. 1862) Since people are by nature poorly equipped to register any but short-term changes, it is not surprising that we fail to notice slower changes in either climate or the sun. John A. Eddy, The New Solar Physics (1977-78) Foreword By E. N. Parker In this time of global warming we are impelled by both the anticipated dire consequences and by scientific curiosity to investigate the factors that drive the climate. Climate has fluctuated strongly and abruptly in the past, with ice ages and interglacial warming as the long term extremes. Historical research in the last decades has shown short term climatic transients to be a frequent occurrence, often imposing disastrous hardship on the afflicted human populations. The 17th century in North America, Europe and China provides an outstanding example of the onset of cold. The principal impact is on agriculture i.e., the food supply, particularly near the northern limits. Famine begets social and political turmoil, as well as pestilence and death. It is as important to appreciate the social impact of the transient cold as it is to understand the cause of the cold. The onset of warm periods has a comparable destructive impact, but in other ways in other parts of the globe, e.g., the prolonged drought in what is now Southwestern United States during the unusually warm 12th century. Recent studies of ice cores from drilling through the Greenland ice cap show occasional strong transients, with the mean temperature dropping a couple of degrees or more over a decade, followed closely by a substantial reduction of atmospheric carbon dioxide. Is such a cold snap initiated by a temporary disruption of the Gulf Stream, for instance? And if so, then what disrupted the Gulf Stream? Then did a worldwide reduction in surface sea water temperatures consume the missing atmospheric carbon dioxide? We may expect that there is no single cause driving a downturn in temperature, or driving the present upturn. The measured rapid increase of carbon dioxide in the atmosphere through the second half of the 20th century is largely a consequence of profligate burning of fossil fuels. We can only conclude that the greenhouse effect of the accumulating carbon dioxide (and other anthropogenic emissions) has a warming effect, while anthropogenic aerosols may push a little in the opposite direction. However, that leaves us wondering about the comparable warming through the first half of the century, when the accumulation of carbon dioxide was slow and slight. There we turn to the inconstant Sun. The history of the scientific detective work that has led to the present partial understanding of the brightening Sun (since about 1880) is fascinating. The work really got underway with the invention of the telescope around 1610 and extends through the ongoing contemporary studies of atmospheric physics and of solar and stellar variability. It is fair to say that the scientific inquiry thus far has established the enormous complexity of the 20th century warming problem. The two major drivers appear to be the varying brightness of the Sun and, of course, the accumulating greenhouse gases. These are imposed on the diverse dynamical modes of circulation of the terrestrial atmosphere and oceans. Indeed, it has been proposed by some that the decadal – and even century long – swings in climate might be nothing more than the natural consequence of nonstable modes of atmospheric circulation. That is to say, the climate cannot settle down because there is no truly stable mode into which to settle. This view is perhaps too simple, but it makes the important point that the wandering and never- stable climate is hypersensitive to both external and internal stimuli. The slight deflection by a small tweak may divert the atmosphere into a diverging dynamical path. We would not go so far as to apply the popular saw from chaos theory that the fluttering of a butterfly in the rain forest of 1 the Amazon basin may ultimately strongly influence the rainfall in Tennessee. We reject the applicability of this vivid overstatement for the simple reason that the atmosphere is buffeted so much more strongly by other effects. For instance, the eruption of Mt. Pinatubo represented a “butterfly” of much greater vigor than any Amazonian lepidopteron. However, we cannot escape the fact that seemingly small effects may, by their special nature, ultimately lead to large consequences. Thus, in our search to understand the climatic changes, past and present, we should not immediately reject an exotic idea as absurd until we can be sure that we fully understand the sensitive atmosphere. And that full understanding of the dynamical atmosphere, with its 3D hydrodynamics, cloud formation, coupling to the dynamic oceans, and coupling to the mountainous topography, lies many years in the future. Thus we must give consideration to a variety of unsubstantiated, and even dubious, ideas. We must keep in mind that absence of understanding of an effect is not the same thing as understanding that the effect cannot be. Many current ideas will ultimately prove to be false or inaccurate, just as many old ideas have already fallen by the way. One of the most frustrating aspects of the origins of climate variation is the intermittent nature of some of the effects. An example is the sometime solar correlation of the formation of troughs at the 100 mbar level over the north Pacific Ocean. The effect appears to come and go with the varying surface sea water temperatures through El Niño and La Niña. Or are we just kidding ourselves and there really is no connection with solar activity? Then what can we say about the once well established, but now long vanished, correlation of the level of Lake Rudolph (now Lake Turkana) with the solar sunspot cycle? Drought in the high prairie in the western United States in association with the deep sunspot minimum that occurs every 22 years seems now to be a statistically robust effect, but the physical connection remains mysterious. So what are we to think? H. Svensmark has recently pointed out the remarkably close correlation between cloud cover and the cosmic ray intensity, closer than with any other index of solar activity. The connection here would presumably be through the nucleation of aerosols, water drops, and ice crystals by the atmospheric ions created by the passage of cosmic ray particles. If the effect is real, it represents a highly leveraged control on climate. Unfortunately we do not know enough physics and chemistry of cloud formation to pass judgement at the present time. Then to what extent does the temperature of the upper stratosphere influence the dynamics of the jet stream and the troposphere? The temperature of the upper stratosphere varies widely between solar maximum and minimum. Some atmospheric models have shown a substantial coupling to the dynamical behavior of the lower atmosphere, while others find little or no effect. Progress in understanding cloud formation, the global dynamics of the atmosphere and oceans, the quantitative ocean-atmosphere carbon cycle, nitrogen cycle, etc, will eventually clear away the rubbish and leave the gems. However there are a lot of laboratory work and observations in the field before that will be possible. The worst mistake a scientist can make is to assert prematurely that some exotic new effect “cannot be” because our present limited knowledge does not cover the effect. Certainly some ideas are without a known physical basis at the present time. They should be catalogued under some such heading as “Curious idea, presently dubious, to be kept clearly in mind as the science progresses”. The history of ideas on terrestrial climate and weather change and the history of ideas on the magnetic activity of the Sun can be traced back to ancient times. Some of the historical interpretations of the observations bring smiles to our faces today. But it must be remembered 2 that interpretation is the first essential step in setting up the possibility of negation, the crucial step in any scientific investigation. The effort to establish a coherent body of knowledge of climate variation and solar activity variation has been fascinating and protracted. A connection between the two has been speculated off and on for at least a couple of centuries, but only with the concept of quantitative statistical correlations has it been possible to make serious progress, and only with the advance of physics and technology has it been possible to pursue the actual mechanisms. There is no single point in time when the science of the connection got underway, but the modern phase, connecting global climate with the activity of the Sun, was initiated by E. Walter Maunder just a little more than a century ago. Maunder’s principal contribution was to emphasize the varying level of solar activity over the centuries since the advent of the telescope, with particular attention to the scarcity of sunspots from about 1645 to 1715, beginning only 35 years after the start of telescopic observations.