Maunder Minimum

Willie Wei-Hock Soon, Steven H. Yaskell, MultCo 523.7 S711m 2003

A strange book. The claim is that temperature variations are the result of solar output variations, and that the Maunder sunspot minimum was responsible for the "Little Ice Age" in the 1600s, and at other times.

What the authors do not explain is how a massive object like the sun can cool so rapidly. The observed solar cycle is 1366 ± 0.5 watts, mostly associated with changes in UV emission. That is significant, and measurable, and its main effect on climate is changes in ozone and changes in the location of the jet stream. As I write this in January 2016, my 4th cousin in Sweden reports there has not been any snow, and spring flowers are budding in New York. Last year at this time, both places were fiendishly cold. And Oregon, where I live, did the opposite. Where the cold polar air went in the 1600s is probably as variable as it is today, while the Sun just keeps ticking along like the giant thermal mass that it is.

There are many jarring statements. On page 123, a claim that the sun's magnetic field is "inverse-square, in contradiction to Kelvin", with a citation to the 1989 "The polar heliospheric magnetic field", Jokipii and Kota, GRL 1989. That indeed shows an inverse square relationship at the poles. The sun's axial tilt to the ecliptic is 7.5 degrees, we are near the sun's equator, and the usual magnetic dipole inverse-cube relationship ought to apply.

The claim that solar wind and magnetic fields influence climate are hard to comprehend. The magnetopause is about 5 radii out, where the earth's dipole field is 125 times weaker (the earth's field IS inverse cube, and we've measured that directly with satellites). At the earth's orbit, the solar wind pressure ranges from 1 to 6 nanopascal, and the fast solar wind moves at 750 km/s. The power flux is the pressure times the velocity, so the power entrained in the solar wind is a maximum of 6e-9 * 7.5e5 or 4.5 mW/m² - since black body temperature is the 4th root of power, the temperature effect would be approximately (1/4) * 300K * 4.5e-3 W/m² / 1366 W/m², or about 250μK; since the earth's temperature lapse rate is 6.4 K/km, this is the temperature change corresponding to a 4 centimeter altitude change.

Soon ignores a measurement problem - we were not accurately measuring solar output, or temperatures outside of Europe, during the so-called "Little Ice Age", so we really don't know how widespread it was. There is evidence of changes in some places - but was it global? Unlike most critics of this book, I think there was a global effect, but it was partly anthropogenic as well.

William Ruddiman explains the lower temperatures of the 1600s as a drop in CO₂ caused by the end of slash-and-burn agriculture by American Indians, after they were ended by smallpox. Others point at a lot of volcanic activity at that time. Invoking large Solar variations with no direct photometric evidence, or an explanation of this contradiction of known stellar physics and decades of astronomical observation of thousands of G2 stars, makes this book's hypothesis very unlikely. We do not have to guess about past solar variation when we can look at contemporary stellar variation.

Soon is alleged to take money from oil companies - well, I give money to oil companies every time I fill up at the gas station (about 10 times a year, I don't drive much). My revealed economic preference is to support Soon, even though I disagree with his claims. Color me hypocritical. Soon calls himself an astrophysicist, though he trained as an aerospace engineer, with a PhD from USC in 1991. Presumably he learned something about astrophysics in the subsequent 25 years, but his academic publications are (like mine) rare.

I have not read the whole book - I read some, and skimmed the rest paragraph by paragraph, looking for scientific statements. Perhaps someone else has analyzed it in detail, but for now it goes next to Plimer on the "please don't let this happen to me" bookshelf.