Earth is experiencing a sunspot drought which, if it persists, may deliver a make-or-break test of the theory of anthropogenic global warming (AGW).
Along with a dearth of sunspots, NASA reports other signs of a current lull in the sun’s activity, including a 50-year low in solar wind pressure and a 12-year low in the sun’s brightness.
Some scientists believe that these signs point to more than just a low point in the 11-year solar cycle. The sun may be entering a “deep solar minimum”.
Previous solar minimums – the Maunder Minimum of 1645-1715, the Sörer Minimum of 1460-1550 and the Dalton Minimum of 1790-1830 – coincided with periods when Earth’s climate was colder than average.
While the link between solar minimums and a dip in global temperature isn’t fully established, some believe a solar minimum over the next couple of decades may be a litmus test of whether greenhouse gas emissions are the primary cause of Earth’s sudden warming.
Among them is University of New England researcher, Dr Robert Baker, who has for several years worked on a theory that the sun is a key driver of Australian rainfall.
The Dalton minimum occurred at about the turn of the 18th Century, and another minimum was recorded at about the turn of the 19th Century.
If this roughly 100-year pattern repeated, Dr Baker believed we may be in for another multi-decade minimum with correspondingly lower global temperatures.
“If we have a solar minimum and global temperatures continue to climb over the next decade, it will have established carbon dioxide as a potent force on the Earth’s climate,” Dr Baker said.
“It’s going to be a very good scientific test of carbon’s real effect.”
Dr Baker said the sun’s influence on global climate was underestimated.
He has for several years been tracking 11-year solar cycles against the Southern Oscillation Index (SOI), with remarkable accuracy – until this year, when the relationship suddenly fell apart.
Dr Baker believed this may be because the solar minimum had overridden the smaller cycles he’d been tracking.
He was now working on a paper outlining a theory that the sun’s cycles influenced rain-bearing cloud over the Pacific Ocean.
How much cosmic radiation entered the Earth’s atmosphere, and how far it penetrated, in Dr Baker’s view largely depended on the polarity of the sun and Earth’s magnetic fields.
His idea was when the Earth’s magnetic field had been neutralised by negatively-charged particles from the sun, certain forms of cosmic radiation entered the atmosphere and encouraged plankton development in the oceans.
Plankton give off dimethyl sulphide, which is regarded as a potent agent of cloud nucleation – that is, water molecules cluster around the compound to the point that rain droplets are formed.
Other forms of radiation in other cycles killed off plankton, Dr Baker believed, inhibiting cloud formation.
Dr Baker said he had found a relationship between these processes and the El Nino-La Nina cycles.