It was the Sun wot done it. Or was it?

A sharp drop in solar activity could soon tell us how much mankind and the Sun are responsible for warming the planet
Stuart Clark

Like it or not, it will soon be time to start placing bets for a white Christmas. If most climatologists are to be believed you are almost certainly throwing your money away.
The onward march of global warming is consigning such traditional Christmas card scenes to history. No more deep and crisp and even winters for Britain, replaced instead by damp and slush and stormy.
But, if a small group of maverick scientists are right, the chances of Yuletide snow may rise dramatically over the coming decades.
The difference of opinion hinges on what role — if any — the Sun plays in climate change. The vast majority of climate scientists maintain that the solar influence is limited or even negligible, and it is the unsustainable growth of industrialised nations that is driving the climate into chaos. The mavericks contend that the Sun’s activity dwarfs the human contribution, and that there is nothing we can do except wait for the Sun to change.
The public seems to agree with the mavericks. In a recent poll for The Times, only 41 per cent of UK voters thought the case for man-made global warning had been proved. Now, by a quirk of nature, the Sun has presented us with a golden opportunity to resolve this debate once and for all.
Satellite measurements for the past 30 years show that the Sun’s energy output has remained remarkably constant. What is changing is the level of solar activity. Solar activity governs the appearance of sunspots — dark blemishes on the solar surface. Sunspots form where magnetism reaches out from the Sun into space. In times of high solar activity, sunspots pockmark the solar surface for years and the Sun’s magnetic field balloons outwards to shield the Earth from deep space particles called cosmic rays.
According to the mavericks, cosmic rays induce clouds to form when they strike our atmosphere and low-level clouds are thought to reflect sunlight, cooling the Earth. So, when solar activity is high, the Earth is protected from cosmic rays and fewer clouds are formed. Thus, more sunlight reaches Earth’s surface and the planet heats up.
But how to prove this? During the 20th century, solar activity rose steadily, as did the amount of industrial gases being pumped into the atmosphere. With both quantities rising, it has been impossible to distinguish between them. Now, that has all changed.
In the past 12 months solar activity has fallen to levels unseen since the 1920s. Sunspots have become rare sights and for three quarters of this year the Sun has been spot-free. According to one study if the trend continues at its current rate, the Sun will lose its ability to produce sunspots by 2015. That would take it back to its condition in the latter 17th century, when hardly any sunspots appeared for 70 years — and Northern Europe underwent the worst years of the so-called Little Ice Age.
Winter scenes from this period were romanticised by artists such as Brueghel painting frost fairs and hunting scenes. But was the 17th century sunspot crash responsible for the Little Ice Age or a coincidence? Could we now find ourselves plunged into a similar freeze if the sunspots do not return?
The answer to the latter is, presumably, yes if the Sun is solely responsible for climate change; no if the mainstream is correct and solar influence is negligible. With this in mind, tonight in Bruges, I am chairing a public debate for the sixth annual European Space Weather Week between world authorities on solar variability who represent all sides of this discussion and have differing opinions about the Sun’s influence on climate. Topping the agenda is the sunspot crash and the opportunity that it presents. The plunging solar activity level will effectively remove the solar influence on climate change. If we are vigilant and honest about any slowdown in warming, its amount will tell us exactly how much the Sun was contributing.
The smart money is on the level of solar contribution being somewhere between the two extremes. In other words, both solar activity and industrial gases play a role. There is credible scientific work that ascribes up to a third of current warming to solar influence. Studies show that the Earth’s temperature mirrored solar activity until the 1980s. Then the number of sunspots stabilised but the temperature continued to rise. In other words, something overtook the Sun as the primary driver of the Earth’s temperature. That is generally thought to be industrial gases.
Now the test can be made. It is time for all sides to put away the rivalry and begin to work together. Observations must be made, experiments performed and all data must be published, not cherry-picked. This golden opportunity to reach consensus must not be squandered.
Above all, we must not let any downturn in temperatures be used as an excuse by reluctant nations to wriggle out of pollution controls. Just as certainly as the solar activity has gone away, so it will return. If we have done nothing in the interim to curb man-made global warming, we will be in worse trouble than ever.
Dr Stuart Clark is the author of The Sun Kings: The Unexpected Tragedy of Richard Carrington and the Tale of How Modern Astronomy Began (Princeton)