THE NEXT SOLAR CYCLE And why it matters for climate David Whitehouse The Global Warming Policy Foundation Note 22 Contents Summary 1 About the author 1 Introduction 3 Solar variability 3 The Little Ice Age 4 Blaming sunspots 4 A sunspot cycle 5 The Maunder Minimum 6 A magnetic cycle 7 Cycle 24 8 Cycle 25 9 Coda 11 Notes 11 About the Global Warming Policy Foundation 12 The Next Solar Cycle and Why it Matters for Climate David Whitehouse Note 22, The Global Warming Policy Foundation © Copyright 2020, The Global Warming Policy Foundation ‘Any coincidence is always worth notic- ing. You can throw it away later if it is only a coincidence.’ Agatha Christie, Nemesis. Summary Predictions for the next solar cycle – Cycle 25 – range from very low activity to stronger than Cycle 24. The National Oceanic and Atmos- pheric Administration’s Solar Cycle Prediction Panel says there is no evidence for another period of very low activity, as in the Maunder Minimum of the late-17th and early-18th cen- tury, which could have an important effect on factors that govern the Earth’s climate. Never- theless, there is no consensus and it remains a possibility. About the author The science editor of the GWPF, Dr David- Whitehouse is a writer, journalist, broadcast- er and the author of six critically acclaimed books. He holds a PhD in astrophysics from the Jodrell Bank Radio Observatory. He was the BBC’s Science Correspondent and Science Editor of BBC News Online. Among his many awards are the European Internet Journalist of the Year, the first Arthur C Clarke Award and an unprecedented five Netmedia awards. As- teroid 4036 Whitehouse is named after him. 1 2 Introduction 2019 was mostly without sunspots. For a long period, the Sun was spot-free for 90% of the time, making the period of minimum activity at the end of Solar Cycle 24* and the beginning of Cycle 25 one of the deepest solar minima ever observed. Understanding the 11-year solar cycle is important, not just for the science of the Sun, but also for appreciating and predicting its influence on Earth and its climate. The Sun is changing its behaviour, and is not acting the same way as it did 50 years ago, when solar cycles were stronger than they are today. How significant is this change? Could the solar cycle behaviour be about to influence the Earth’s climate, as some think may have happened 350 years ago? Are we able to make predictions of future solar cycles and be forewarned of their climatic influence? This note discusses some of these issues. Solar variability It can be very easy to dismiss the Sun as having far too little variability to have an effect on the Earth’s climate. The fluc- tuations of total solar radiation averaged over the electro- magnetic spectrum amount to just 0.1%. However, a much larger variability occurs in the flux of energetic particles and short-wavelength radiation over the 11-year solar cy- cle, and these changes have effects in the upper regions of the atmosphere. Changes of up to 10% occur in the amount of ultraviolet light leaving the Sun over a solar cycle. It has been suggested that, averaged over the globe, the Earth’s surface warms by as much as 0.1°C over the 11-year cycle from solar minimum to solar maximum, and some regions may experience considerably more warming than the aver- age. Cyclical warming of 0.1° C is important, given the scale of global temperature increase observed this century. Also, any prolonged reduction in solar activity could have dec- ades-long effects on the Earth’s temperature. It is important to understand the solar cycle and the predictions of its be- haviour in the future. Some have suggested that the significant variations in climate can only be explained if the influence of the Sun has been underestimated by a factor of about five.1 Svensmark obtains a similar result derived from temperatures since the Medieval Warm Period, as estimated from boreholes.2 This implies there would be a decrease of at least 1°C if a new deep solar minimum occurred. * For convenience, solar cycles are numbered starting in 1755 with Cycle 1. Since 1 July 2015, the original sunspot number data have been replaced by a new entirely revised data series. 3 The Little Ice Age There are many ways to estimate the Earth’s climate over the past 1000 years or so. Scientists have been ingenious in find- ing what they term ‘proxies’ – measurements that in some way reflect the climate. These are an impressive array of phe- nomena: tree-rings, stalagmites, boreholes, pollen counts, sea sediments, corals, ice cores and mountain glacier de- posits. The remarkable thing is that (aside from the past 30 years or so) they generally agree that in the past millennium or so there have been two global climate anomalies: the so- called Little Ice Age (LIA), which stretches from 1300–1900 AD, and the Medieval Warm Period (MWP), from 800–1200 AD. Evidence is found all over the world: in sediments as- sociated with the Indo-China Warm Pool (the largest body of warm water on Earth), in lake sediments in South America, and from radioisotope analysis of shells on the shores of Greenland. These two climatic events are not just European, as was once thought, but more global in nature. For centuries, many French villages have recorded the date at which the local grapes have ripened. This data shows that, starting in the mid-17th century, harvests began one or two weeks later than before. Cereal production also slumped in the mid-17th century. The LIA affected Europe at just the wrong time. In re- sponse to the more benign climate of the MWP, Europe’s population may have doubled. More people married, and most did so earlier, giving birth to six or seven children de- spite – or perhaps because – infant mortality was high. But in the mid-17th century, demographic growth stopped, and in some areas fell, in part due to the reduced crop yields. Bread prices doubled and then quintupled. Buying bread now absorbed almost all of a family’s income. This in turn caused a collapse in demand for manufactured goods and thus to high unemployment. High prices and reduced incomes forced many couples in Europe to marry later; the average age of brides rose: they were typically teenagers in the later 16th century, but were putting off getting married until age twenty-seven or twen- ty-eight in the mid-seventeenth, thus reducing the birth rate. Hunger weakened the population. To paraphrase the English philosopher Thomas Hobbes, writing about political philosophy in 1651, ‘the life of man [is] solitary, poor, nasty, brutish, and short’. Blaming sunspots During the English Civil War (1642–1651), a preacher told the House of Commons in London, ‘these are days of shaking… and this shaking is universal: The Palatinate, Bohemia, Ger- many, Catalonia, Portugal, Ireland, England.’ Later the Tsar of 4 Muscovy was told, ‘The whole world is shaking, and the peo- ple are troubled.’ There were upheavals in the Ottoman Em- pire, Portugal, Sicily, Spain, Sweden, and the Ukraine, as well as Brazil, India, and China in the world beyond. Ralph Jos- selin, an English vicar, wrote, ‘I find nothing but confusions.’ Josselin looked towards God’s inscrutable purpose, but oth- ers looked elsewhere. The Italian historian, Majolino Bisac- cioni, suggested that the wave of revolutions might be due to the influence of the stars, but Jesuit astronomer Giovanni Battista Riccioli speculated that fluctuations in the number of sunspots might be to blame. Something was happening to the Sun, and astrono- mers and philosophers of the time knew it. The early users of telescopes had seen numerous sunspots but, from the 1640s to the early 18th century, they noted with alarm their almost total absence. When Giovanni Cassini, the director of the Paris observatory, saw one in 1671 the Philosophical Transactions of the Royal Society of London at once reported it, adding a description of what sunspots were, because the last one had faded away a decade before and readers might have forgotten. In May 1684, John Flamsteed, the first Astronomer Roy- al, wrote ‘tis near seven and a half years since I saw one be- fore they have been of late so scarce, however frequent in the days of Galileo and Scheiner’. After an absence of almost a century, sunspots and the northern lights came back suddenly in the second decade of the 18th century. The sun had been in a long period of low activity, but it had now awoken and the particles it was fling- ing into space struck the Earth’s upper atmosphere, causing the rarefied air to light up the night skies of northern Europe and America. The 1780s in particular were a good decade for the northern lights. No one had seen such fine displays in living memory. In addition, two great volcanoes erupted – Laki in Iceland and Asama in Japan – and piled the strato- sphere with enough dust to shield the sun and lower global temperatures. For months, the dust meant glorious sunrises and sunsets. It all made a deep impression on the youth of the time. Wordsworth called them ‘northern gleams’, while Coleridge said they were the ‘streamy banners of the north’ and ‘floating robes of rosy light‘. A sunspot cycle A few decades later came an important discovery. In 1826, the German amateur astronomer Samuel Heinrich Schwabe (1789–1875), set himself the task of discovering planets in- side Mercury’s orbit, whose existence had been conjectured for centuries.