Ice-Age 2: Weak Sun Will Not Cause Ice Age

Published: 11:39 PM GMT on July 26, 2015

Ice-Age 2: Weak Sun Will Not Cause Ice Age (from Mike Liemohn)

Links to earlier in series
Ice-Age 1: There’s a Mini-Ice Age Coming? Good Timing!

The Daily Mail held out some bait on global-warming obfuscation, reporting that scientists warning of a mini-Ice Age. I want to explore this article in a number of ways, and I want to see if we can think about how to manage the influence of the article. Thanks for the excellent comments on the previous blog.

Here is the blog from Professor Mike Liemohn.

Dr. Rood asked me, a space physicist in the same department at the University of Michigan as him, to comment on the recent media report like the one here of an impending Little Ice Age. While we are in solar maximum, when Sun's magnetic activity is high and sunspots are seen across its surface, this particular solar maximum has been quite small. There are some solar physicists predicting that the next few solar maxima will also be small, with the Sun entering an extended interval of very low magnetic activity, called a Maunder State. We have only seen this once before, in the 1600s shortly after Galileo invented the telescope and people began keeping routine and reliable sunspot records. For nearly 70 years in the 1600s, the sunspot cycle was very small, often going months without any spots at all.

Sunspots are regions of strong magnetic bundles poking through the Sun's surface. To maintain pressure balance, the local gas is both less dense and cooler, resulting in a dark patch on the solar surface. Therefore, a sunspot reduces the output of sunlight, known as total solar irradiance or TSI (Excellent NASA resource on Solar energy). At first thought, it seems that a reduction in sunspot activity should, therefore, increase the Sun's TSI. This isn't correct, though, because sunspots are accompanied by another feature of the solar surface, faculae. Faculae are bright spots on the Sun, where the solar magnetic field pries open the surface just a bit to reveal the hotter gas just inside the Sun. One sunspot will be accompanied by dozens, perhaps hundreds, of these smaller faculae. So, there is a competition between faculae and sunspots for dominance of the TSI during the solar cycle.

All of these changes to TSI, however, are small. Tiny, in fact. A single sunspot might lower TSI by 0.1 – 0.3%, perhaps up to 1% for a big sunspot cluster. This influence on TSI will only happen, though, when the sunspot is right near the solar disk center. The influence is directional and the effect of a sunspot on TSI only lasts a day, maybe a few days at most. Faculae, however, have the most influence on TSI when seen from an angle, and therefore influence TSI for their entire traversal across the Earth-facing solar disk, which is roughly two weeks. Added up over the whole disk from all faculae, and the TSI contribution is a continuous increase of, yep, a few tenths of a percent. The net result is actually an increase of about 0.2% in TSI during high sunspot intervals, with occasional very brief excursions down to about equal negative values when a big sunspot cluster passes by.

TSI, therefore, doesn't change very much over the solar cycle. This plot shows TSI (irradiance), Sunspots, Solar Flare Index, and 10.7 Radio Flux (from Wikipedia Solar Variation).



The running average values seen in this plot show an increase at solar maximum of about 0.1% in TSI (irradiance) relative to solar minimum values. This small change is why the solar photon flux at Earth is often referred to as the Solar Constant. Climate scientists have examined the influence of this solar cycle variation in TSI on Earth's temperature, concluding that the impact is most likely in the 0.1 – 0.2 ˚C range. That is, during solar maximum years, the Earth is a little bit warmer than it is during solar minimum years. Not enough that you would notice, though, and not nearly as big as the influence of increased "greenhouse gases" like carbon dioxide.

Therefore, even if the Sun enters into a Maunder State and has several solar cycles with very low sunspot numbers, it will mean that TSI will hover at the lower end of its usual TSI oscillation. It will still be very close to its historical values and we can still call it the Solar Constant. So, I agree with reports like this that predict a global warming speed-up, not an impending Ice Age.

Mike Liemohn

Thank you Professor Liemohn.

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In the spirit of scholarship and the next entries in this series. The Daily Mail story relies largely on the research of Professor Valentina Zharkova. Here is the abstract of the Professor’s Zharkova’s talk at the Royal Astronomical Society’s National Astronomy Meeting 2015. Here is a link to Professor Zharkova’s web page at University of Northumbria in New Castle, U.K.. Professor Zharkova is a Fellow of the Royal Astronomical Society (FRAS). I reproduce the abstract at the end of the blog.

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Abstract of the Professor’s Zharkova’s talk

Heartbeat of the sun derived with principal component analyses and prediction of solar activity on millennium scale


In this talk we present new results of principal component analysis of the solar background magnetic field and sunspot magnetic field measured in the cycles 21-24 by Wilcox Solar Observatory and SOHO/MDI. We report a pair of principal components (PCs) of magnetic field waves covering more than 30% of the data variance and attribute these components to dynamo waves generated in two layer dynamo model. We derive mathematical laws describing these dynamo waves and describe their link to the solar activity index of sunspot numbers. Using the derived laws we predict the solar activity backward and forward for two millenniums and reveal close fit to all the observed activity features and the presence of a long-term activity cycle of 320-400 years in addition to the regular 22 year cycle. Preliminary interpretation of the PCA results with the modified Parker's two layer dynamo model accounting for both cycles (22 and 350 years) is also discussed.

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About The Author
I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.

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