This isn’t going to help anyone caught in the Melbourne heatwave, but the sun is getting cooler.

Not by much, only by around 0.1 C averaged across the planet according to NASA’s Goddard Institute but enough to make a cooler sun the hottest emerging topic in the debate about global warming.

The Goddard Institute says it “expects a new global temperature record will be set in the next 1-2 years, despite the moderate negative effect of the reduced solar irradiance.”

But then again, its forecasts about when the next solar cycle would begin, supposedly in the second half of 2007, are now wrong by two years. And the doors to the doubters, ranging from the barking mad to the scrupulously forensic — when it comes to the industrial greenhouse gases contribution to climate change — have been kicked open.

Something interesting is happening on the sun. There have been very few sunspots, which are a proxy indicator of solar irradiance, for the last year. The transition from one solar cycle of around 11 years to the next is marked by the appearance of new sunspot. With a different magnetic polarity, yet new and old cycle sunspots have been increasingly rare, or non-existent, for much of the last 12 months or more.

This means a really big field test, one as big as the earth, is being applied to mutually exclusive viewpoints, that there is no proven nexus between small scale solar variability and climate, or that there is.

It will challenge the orthodoxy that anthropogenic inputs are largely or completely to blame for a warming world, or the unfashionable minority view, that they count for something between zero and “not much.”

So far, just about every supporter of anthropogenic global warming or AGW, has run away from discussing the inconvenience or otherwise of a “quiet” sun.

But there are some interesting things to keep in mind. The last well observed slippage from an 11 year solar cycle to a 13 year cycle preceded the Dalton Minimum, a set of three and a bit solar cycles between 1790 and the mid to late 1820s when the sun was very, very quiet, and the world coincidentally or otherwise, rather cool, with widespread crop failures exacerbated by the early social upheavals of industrialization.

The last long and directly observed period of a largely spotless sun was the Maunder Minimum, of 1450-1540, which coincided with the middle of the Little Ice Age, which by varying criteria, is dated as starting as early at the mid 1300s and ending by the mid 1800s, including the Dalton Minimum, even though some argue that it really ended in the mid 1700s, when the UK stopped imitating Iceland.

How could a drop in 0.1 C in incoming solar irradiance possibly cause so much calamity? Many of the suggested mechanisms involve changes to cloud cover, arguing that the voluminous low level billowing clouds captured by the landscape artists of those times were not just a fad, but real, and capable of reflecting much more solar energy back into space and thus significantly cooling the surface.

Others argue that thermally induced changes to ocean currents, particularly the inhibition of the warming Gulf stream that keeps Europe abnormally temperate, were responsible for allowing Siberian weather patterns to invade middle Europe.

After the marked retreat of north polar sea ice last summer, the seasonal freeze began early. At this stage, subject to sudden warming, the Arctic sea ice outlook for 2009 is “lots”.

One thing is certain. The current solar cycle that was supposed to last 11 years has lasted nearly 13 years. That won’t change.

The question now becomes, what will change?

Peter Fray

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