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David Whitehouse: Will Inactive Sun Cause Global Cooling?

David Whitehouse, Public Service Europe

The weakness of Cycle 24 indicates that we might be entering a period of low solar activity that may counteract man-made greenhouse temperature increases. Cold not warmth might be our future. We do not know. We must keep watching the sun.

Something is happening to our sun. It has to do with sunspots or rather the activity cycle their coming and going signifies. Sunspots – dark magnetic blotches on the sun’s surface – come and go in an 11-year cycle of activity first noticed in 1843. It is a process related to the motion of superhot, electrically charged gas inside the sun; a kind of internal conveyor belt where vast sub-surface rivers of gas take 40 years to circulate from the equator to the poles and back.

Somehow, in a way not very well understood, this circulation produces the sunspot cycle in which every 11 years there is a sunspot maximum followed by a minimum. In the last century, the sun’s activity may have been the highest for more than 8,000 years with lots of strong solar cycles. But then things turned. The recent cycle – so called ‘Cycle 24′ – is puny. If history is anything to go by, then the sun’s change of mood could affect us all by cooling the earth and throwing our climate change calculations into disarray.

Not all sunspot cycles are the same. They can be long or short, weak or strong and sometimes they can go away altogether. Following the discovery of the cycle, astronomers looked back through previous observations and were able to clearly see it until they reached the 17th century when it seemed to disappear. It turned out to be a real absence, not one caused by a lack of observations. Astronomers called it the Maunder Minimum.

It was an astonishing discovery, our sun can change. There was something different about the sun back then. Between 1645 and 1715, sunspots were rare. About 50 were observed. There should have been 50,000. Ever since the sunspot cycle was discovered, researchers have looked for its rhythm superimposed on the earth’s climate. In some cases, it is there but usually at low levels. But there was something strange about the time when the sunspots disappeared that left scientists to ponder if the sun’s unusual behaviour could have something to do with the fact that the 17th century was also a time when the earth’s northern hemisphere chilled with devastating consequences.

Scientists call that event the Little Ice Age and it affected Europe at just the wrong time. In response to the more benign climate of the earlier medieval warm period, Europe’s population may have doubled. But in the mid-17th century, demographic growth stopped and in some areas fell – in part due to the reduced crop yields caused by climate change. Bread prices doubled and then quintupled and hunger weakened the population.

The English preacher John King wrote: “Our years are turned upside down, our summers are no summers; our harvests, no harvests.” Ralph Josselin, an English vicar, wrote: “I find nothing but confusions.” But while Josselin looked for God’s inscrutable purpose, others looked elsewhere. The Italian historian Majolino Bisaccioni suggested that the wave of bad weather and 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. For he too had noticed they were unusually absent.

The key point is that looking back through the sunspot record reveals many periods when the sun’s activity was high and low – and in general they are related to warm and cool climatic periods. For example, as well as the Little Ice Age there was the weak sun and the cold Iron Age, the active sun and the warm Bronze Age. Scientists cannot readily explain how the sun’s activity affects the earth but it is an observational correlation that the sun’s moods have a climatic effect on the planet.

The big question is what will happen in the future. Cycle 24 is weak with few sunspots. Could it be that our sun is behaving like it did in the 17th century? Could we be on the verge of a new Little Ice Age? The last decade has been warmer than previous ones. It is the result of a rapid increase in global temperature between 1978 and 1998. Since then, average temperatures have held at a high although steady level. Many computer climate projections suggest that the global temperatures will start to rise again in a few years’ time. But crucially those projections do not take into account the recent change in the sun’s behaviour.

The weakness of Cycle 24 indicates that we might be entering a period of low solar activity that may counteract man-made greenhouse temperature increases. Some members of the Russian Academy of Sciences say we may be at the start of a period like that seen between 1790 and 1820, a minor decline in solar activity called the Dalton Minimum. It is something we must take seriously because what happened to the sun in the 17th century is bound to happen again sometime. It might even be the case that the earth’s response to low solar activity will overturn many of our assumptions about man’s influence on climate change. Cold not warmth might be our future. We do not know. We must keep watching the sun.

Dr David Whitehouse is an astronomer and author of The Sun: A Biography

Public Sercice Europe, 24 July 2013