Sun's activity not to blame for climate change

All quiet on the solar front, research shows

People are a contrary bunch. Nothing demonstrates this more clearly than the recent fashion for dismissing global warming as a load of hot air. Indeed, it has become de rigueur to attribute recent increases in global temperatures to something other than human industrial activity and the consequent emission of various greenhouse gases, CO₂ among them.

One suggestion much loved by the sceptics is that solar activity can explain away the warming planet. Indeed, there is plenty of evidence to suggest that long-term variations (over a century or so) in solar output can influence climate. The tabloid inference is that it is then quite alright to continue hunting baby pandas from turbo-charged Humvees.

Now, Rutherford Appleton Laboratory's Professor Mike Lockwood, and the University of Southampton's Claus Fröhlich have analysed the activity of the sun since 1985, to see if any of this "solar climate forcing" is detectable in recent data. They found that although we have witnessed a long period of intense activity, in the last 22 years solar activity has been on the decline, and cannot be used to explain the rapid rise of global temperatures.

Their findings will not surprise many in the scientific community, they say, but should be of interest to the producers of The Great Global Warming Swindle, a television program that aired in the UK this March. The makers questioned the existence of a scientific consensus on the causes of climate change, and put forward solar activity as an alternative explanation for our warming planet.

"That program was so bad it was almost fraudulent," Lockwood says. "[The subjects raised] made for a decent scientific debate 15 years ago, but the questions have since been settled."

He says that there are strong indicators that the activity of the Sun can influence climate. The pre-industrial climate does appear to have been influenced by the Sun: for instance data from ocean sediments and ice sheet samples show that over the last 5,000 years, the monsoon belt has shifted over periods that correlate with changes in cosmic ray flux, which in turn is related to solar activity.

"There are very stong indictors that there was solar control of the pre-industrial climate," he says, refering to changes in global temperatures over the last five to six thousand years. "There is even some, contentious, statistical suggestion that solar heating persisted into the 1940s or maybe even 1950s. But there is almost no evidence that it persisted beyond then."

"All the things we know of that could have influenced climate are going in the wrong direction."

What angers Lockwood more than almost anything is the idea that an interesting area of science was being misused, and that it could be discredited. He stresses that he is not saying that the Sun has no impact on the climate: quite the reverse.

"By falsely applying pre-industrial science to the modern day, the Great Global Warming Swindle risks discrediting a very interesting area of science," he said.

He adds that there are no grounds for suggesting that there is a lag between solar activity lessenning, and a corresponding drop in temperatures, noting that although the solar activity is declining, global heating is accelerating.

"1985 was the highest peak of solar activity in maybe 6,000 years. But the peak is over now, and still temperatures are climbing," he says.

Lockwood and Fröhlich's conclusion is that the global warming we see today cannot be ascribed to solar variability, whichever of the mechanism is invoked and no matter how much the solar variation is amplified. Whichever way you slice it, the overwhelming scientific consensus is that human activity is causing an overall warming of the planet. Yes, there is debate over the finer details of exactly how and how much, but the broad theme is clear.

"The Great Global Warming Swindle raised old debates that are going to be latched on to and used to suggest that we don't need to do anything about climate change. In that sense, it was a very destructive program," said Lockwood.

The paper Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature is published in today's (Wednesday July 11th) edition of the Proceedings of the Royal Society. ®

Bootnote: Ofcom is in the initial stages of investigating a complaint into the scientific foundations of The Great Global Warming Swindle. It says complex investigations are normally completed within two months, so watch this space.