Posted on 19 December 2012 by John Cook

Republished from The Conversation. For a more detailed analysis of the science, check out Dana Nuccitelli's IPCC Draft Report Leaked, Shows Global Warming is NOT Due to the Sun.

The sun’s influence on climate may be smaller than you’ve heard (onlinewoman/Flickr).

Last week, blogger Alec Rawls leaked a working draft of the 5th Assessment Report by the Intergovernmental Panel on Climate Change (IPCC). One section of the IPCC report examines the role of the sun on climate change and concludes that since 1980, solar activity has decreased and had a slight cooling influence on our climate. Over the last few decades of global warming, sun and climate have been moving in opposite directions.

This is hardly a new revelation. In recent years, a number of peer-reviewed studies have investigated the role of the sun on climate change. In 2004, solar researcher Sami Solanki examined solar activity and climate over the last 11,400 years. Upon observing a recent divergence between sun and global temperature, Solanki concluded “solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades”. More recently, UK scientist Mike Lockwood concluded that “…solar forcing has declined over the past 20 years while surface air temperatures have continued to rise…”.

This steady flow of peer-reviewed research finding a negligible solar influence is inconvenient for climate sceptics, who are desperate to blame global warming on the sun (in fact, they’re happy to blame it on anything other than human activity but the sun is the most popular option). How has the sun myth persisted in the face of such a persistent stream of empirical evidence? The most common method is cherry picking.

A striking example of solar cherry picking comes from the Channel 4 documentary The Great Global Warming Swindle, whose main message was promotion of the sun myth. The documentary’s key piece of evidence was a graph of solar activity and global temperature, which infamously ended in 1980 when sun and climate diverge. By cherry picking the data, the producers of The Great Global Warming Swindle attempted to hide the recent decline in solar activity.

The most misleading cherry picks are those where the cherry picked interpretation is the opposite of the conclusion suggested by the full body of evidence. This is the case with Alec Rawls’ interpretation of the leaked IPCC draft. While Rawls’ breaking of a disclosure agreement is unethical, his distortion of the science is more destructive.

Rawls quotes a line from the IPCC draft speculating about a possible mechanism that may amplify the solar influence on climate. From this single sentence, he concludes that the sun must have a greater impact on recent global warming.

One possible mechanism that amplifies the sun’s influence on climate is galactic cosmic rays. The hypothesis, proposed by Danish scientist Henrik Svensmark, is that cosmic rays originating from outside our solar system may seed clouds on Earth. Clouds generally reflect incoming sunlight, which cools our climate. Protecting us from cosmic rays is the sun’s magnetic field, which grows stronger as the sun brightens. When solar activity weakens, more cosmic rays hit the Earth. If cosmic rays do happen to affect clouds, then a weaker sun leads to more cosmic rays causing more clouds, which will have a cooling effect.

The jury is still out on whether cosmic rays amplify the sun’s effect on climate. A number of studies have examined any possible link between cosmic rays and climate and found no link. Reviewing this body of evidence, the current draft of the IPCC report concludes that the cosmic ray mechanism is too weak to have any significant influence on climate.

Regardless of whether cosmic rays or any other mechanism amplifies the sun’s influence, the key fact here is that the solar effect on climate in recent decades has been that of cooling. Any mechanism that amplifies the solar effect would increase the cooling. This is the opposite conclusion to that of Alec Rawls who used a single, isolated sentence in a draft document to support his argument.

Those who reject the scientific consensus on climate change ignore years of research by solar scientists who have repeatedly concluded in study after study that the sun has had a negligible contribution to recent global warming. This is just one part of the accumulating body of evidence that has led the IPCC to release ever strengthening statements on the human role in global warming.

Consequently, the current draft of the IPCC’s 5th Assessment report concludes that it is virtually certain that humans are causing climate change.