The current cycle of the sun is taking a long time to start, triggering different explanations, writes Mark Lawson.
Despite being dismissed by a number of scientists as of little consequence to the present discussion of climate change, the issue of the sun’s activity – or apparent lack of it – has been the subject of considerable debate in recent months. Scientists who concern themselves with the fledgling subject of space weather (changes in the sun’s emissions) have been wondering where all the sunspots have gone, when they might come back and what effect this will have on climate.
The sun has a well-recognised, 11-year cycle marked by spots, or cool dark regions with strong magnetic fields, that appear on its surface. At the peak of the cycle, when the sun may be giving off lots of flares and solar storms that affect satellites, there are lots of spots. At the low part of the cycle there are few to no spots and the sun is calm.
The last solar cycle peaked in 2001 and was pronounced complete by NASAin March 2006. At the same time a team from the National Centre for Atmospheric Research in the US forecast that the next sunspot cycle will be 20 to 50 per cent stronger than the previous one.
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Since then some spots from the new cycle have appeared, as well as – confusingly – some spots from the old cycle which appeared in March of this year. (Scientists can tell which cycle the spots belong to by their magnetic polarity.)
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The next cycle is taking a long time to start, and this lack of activity has prompted observers to invoke the possibility of another Maunder Minimum – a period from 1645 to 1715 with very few sunspots, which is associated with a sequence of bitter winters known as the little ice age.
Scientists have offered two different interpretations for this absence of sunspots, both based on statistical research.
In early July NASA solar physicist David Hathaway pointed out that the solar minimum is still well within historic norms for the solar cycle.
He notes that the average solar cycle lasts 131 months, plus or minus 14 months. By July, cycle 23 (the one just winding up) had lasted 142 months, but it can last much longer, despite NASA’s declaration.
In the early 20th century, the sun was quiet for periods twice as long as the present spell, Hathaway says.
The current cycle has lasted 143 months, with another group saying that although there may be only a few spots, this lack of activity will continue until 2014 when the spots will disappear altogether.
William Livingston and Matthew Penn, both at the National Solar Observatory in Tucson, Arizona, base their forecast on measurements of both the magnetic strength and the temperatures of spots.
Livingston tells The Australian Financial Review that in a trend independent of the solar cycle, the magnetic strength of the sunspots had been declining and their temperature increasing.
They graphed the magnetic field decline and extrapolated it to reach an end point in 2014.
They have forecast that although there may be more sunspots, the present lack of activity will continue until 2014 when there will be no sunspots at all.
As this forecast is based just on what they read from the graphs, rather than on a physical theory, they cannot say what will happen after that, Livingston says.
The pair submitted a paper to Nature three years ago but it was rejected, Livingston says, because it made a strong statement based solely on statistical trends. Recently, however, the paper has been circulated unofficially as part of the climate debate and also because the sun has been quiet. Livingston says he will wait for the right time before resubmitting it.
The role of sun activity in climate is very hotly debated, with the ruling theories emphasising the role of industrial gases, and assigning only a comparatively minor role to the sun in the short term.
But there are dissenters.
Willie Soon, a researcher at the Harvard Smithsonian Centre for Astrophysics in Cambridge, Massachusetts, says he has identified a clear link between the sun’s activity – as indicated by its magnetic activity – and temperature variations in the Arctic and Greenland over 130 years.
Soon tells The Australian Financial Review he chose this area for study as it has good temperature records and is an area sensitive to climate change, so that the signal from any one climatic influence should be easier to spot.
He also says he can point to a physical mechanism in the circulation of the ocean linking the sun’s influence on temperature in the region.
Soon was due to present his results at the 33rd International Geological Conference in Oslo this week. He was co-chairing a sun-climate connection session with Bob Carter, a professor at the Marine Geophysical Laboratory at James Cook University and a noted Australian climate sceptic.
Another scientist who says he has identified a link between the sun’s activity and climate – in particular between rainfall in Australia and sunspots – is Robert Baker, an associate professor at the University of New England’s School of Human and Environmental Studies.
Baker tells the AFR he has identified a strong correlation between sunspots, the sun’s magnetic activity and the Southern Oscillation Index (SOI).
He says variations in the earth’s magnetic field account for about half of the variation in the SOI, and that changes in sunspot activity as an indicator of magnetic activity can be correlated with rainfall patterns in south-east Australia.
The Bureau of Meteorology has rejected Baker’s reasoning and a paper by him was not accepted by the Australian Meterological Magazine. But Baker says his analysis has been accepted by the peer-reviewed journal Solar Terrestrial Physics for publication in December.