The second in Don Kurtz’s excellent series of lectures focused on the plain, ordinary old sun. Now reaching middle-aged, 4.6 billion years old with about another 5 and a half to go, the sun is wondrously active and mysterious. Unlike the earth, which rotates at the same speed at the equator and the poles, because of the sun’s gaseous form it rotates faster at the equator (26 days) than at the poles (35 days). This leads to a highly complex magnetic structure, with the sunspots in essence being where the magnetic loops bulge out of the surface of the sun, forming an area of lower temperature.
Much of the lecture consisted of phenomonal pictures from SOHO, the Solar and Heliospheric Observatory, a satellite constantly aimed at the sun, and the source of much new recent knowledge about our nearest star. Pictures and videos are available online.
Sunspot activity goes in an approximately 11-year cycle. At the beginning of the cycle, sunspots form in bands around 30 degrees from the equator. As the cycle progresses, new sunspots form closer and closer to the poles. The cycle is actually 22 years, as the sun’s polarity flips every 22 years, but this seems to have little effect as far as the earth is concerned.
In his lecture, Don Kurtz summarised the connection between the sunspot cycle and global warming by saying that although the sun does have an impact on global temperature (he mentioned a figure of 0.2 degrees), there’s a far stronger correlation between the level of greenhouse gases (0.6 degrees).
Being a short lecture of 1 hour only, he couldn’t go into it in much more detail, but there’s quite a lot of complexity, and it’s often this complexity that those trying to reach a particular conclusion latch onto when claiming that humans have little or no impact on global warming, or, more ridiculously, that global warming isn’t happening. There’re the Milankovitch cycles, variations of the earth’s orbit, there’s volcanic activity (and, more recently, pollution), which has a cooling effect by reflecting heat away from the earth. There are longer, and as yet relatively speculative, solar cycles.
Much of the complexity comes from looking at what we know, and trying to model what we imperfectly know, or would like to test, and seeing how everything fits. We have fairly accurate temperatature records going back historically. We have fairly accurate carbon dioxide records. But when it comes to the sun, the records are much less accurate.
Sunspot records go back to the 17th century, and the 11-year cycle is clear over this entire period, but there’s information missing in the older records. Sunspots are cooler areas (due to the magnetic effect), but there’s a converse effect – solar faculae, which are the bright spots. These are hotter than normal, but have only been recorded more recently. There’s a correlation between the two cycles, but it’s not perfect, so the records can’t accurately be extrapolated back to the 17th century.
Early scientists were particularly cautious about reaching any conclusions, given how imperfect much of their knowledge was. Some actively tried to show that the sun was predominantly responsible for global warming, such as Sami Solanki, but, after 15 years of research, he was forced to conclude that the sun was not to blame. Now however, there’s little doubt that greenhouse gases have a causal effect on global warming.
After briefly tackling global warming, the highly enjoyable lecture raced onto the Van Allen belts, the bands of highly-charged particles kept from hitting the earth by the earth’s magentic field, and some stunning pictures of the Aurora Borealis, the polar lights. This lead of course to solar storms, with huge amounts of matter blasted from the sun. These happen regularly, but when they’re aimed at the earth, the equivalent of trillions of watts of power arrive in the earth’s atmosphere. The Aurora Borealis go berserk. And, if the storm is strong enough, satellite, radio transmissions, and power transmissions will be affected.
A far, far bigger one happened in 1859 and, if such a storm is repeated, let’s just say you want be reading this online for a while.