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Saturday, September 13, 2008

Non-homogeneity of sunspot numbers a problem, but the more important record of solar activity is in the geologic record

Anthony Watts notes that NOAA has just given a sunspot number to a sunspeck that never in the past would have been given a sunspot number. It is only detectable with a modern magnetogram or a chromosphere image, making today's sunspot numbers higher than earlier numbers for the same level of solar activity.

The most likely explanation for this unprofessional shift in counting standards is political. Global warming alarmist James Hansen has done the same thing at NASA, where as keeper of the GISS temperature records, he has systematically adjusted older temperature data downward to create a heightened appearance of warming. It hurts the alarmist cause to see our current global cooling paired in the popular press with the fact that the sun has gone blank, giving the alarmists a reason to count sunspecks as sunspots. This explanation is especially likely given that NASA's top solar scientist, David Hathaway, is another global warming alarmist (who bizarrely does not provide an opinion on the solar climate relation to the IPCC, but gets his position FROM the IPCC).

That said, the actual scientific importance of consistent sunspot counting should be pretty small. The effect of sunspot activity on global climate seems to come primarily through the large effect that sunspot activity has on the solar-magnetic flux. (It also effects a small increase in solar luminescence.) Not only is the solar flux directly measurable, but in contrast to the sunspot record, which only goes back to Galileo, the solar flux leaves an isotope signature in the geologic record going back many millennia.

When the solar wind is up, it sweeps away some of the galactic cosmic radiation (GCR) that would otherwise hit the earth. It is this GCR that leaves an isotope signature in the geologic record, creating a proxy for the level of solar activity. Fluctuations in the strength of the earth's magnetic field also has to be factored in. (A stronger magnetic field deflects more GCR.) So do fluctuations in the amount of GCR reaching the earth (either from one time events, like relatively close supernovae, or from transit through higher or lower GCR portions of our orbit around the Milky Way). Even without these adjustments factored in, the raw isotope signature is a pretty good proxy for solar activity, which is on average much more volatile than these other determinants of the GCR signal.

It is this GCR record that is most important for understanding the effect of solar-magnetic activity on global climate. Temperature also leaves an isotope signature in the geologic record, allowing direct comparison between temperature and GCR, decade by decade, over the millennia. The results are definitive. GCR "explains" statistically about 90% of the temperature variation on every time scale. (The evidence is amassed in Fred Singer's book Unstoppable Global Warming: Every 1500 Years.)

Since global temperature changes cannot be causing sunspots, it is clear that the sunspots are causing global temperature changes, and with solar activity at "grand maximum" levels from 1940-2000, solar activity easily explains the tiny bit of global warming experienced in the late 20th century.

The sunspot record is still important for solar science. It provides a day by day picture of the 11 year solar cycle going back several hundred years. But people who study the solar cycle can easily take into account a change from not counting sunspecks to counting sunspecks. Anthony Watt's associate Leif Svalgaard says that changing sunspot counting standards is a problem throughout the sunspot record, which exhibits an upward bias as technologies for detecting sunspot activity have become more powerful.

Svalgaard has a review of this history on his own website. The upshot, he says, is that 20th century solar activity maybe was not the highest on record, a conclusion which he says raises some hackles with what he calls "the all time high" crowd.

Does "all time high crowd" really resist correcting the sunspot record?

Having cited the "all time high" reports several times myself, I must say that I can't see any reason why correcting the sunspot record to make it consistent over time would raise anyone's hackles, even if a person WAS improperly "results oriented."

First, the evidence that 20th century warming was caused by relatively high levels of solar activity in no way depends on those levels having been the highest on record.

Second, the "all time high" appellations that I have seen do not come from looking at the sunspot record at all, but come from the GCR record. It was Sami Solanki who coined the "grand maximum" term to describe late 20th century solar activity, after studying GCR isotopes going back 11,000 years. Obviously the GCR record is not affected by any tinkering with the sunspot record.

Svalgaard does not provide any evidence for his claim that correcting the sunspot record:
is controversial and is being met with stiff resistance from the ‘all-time high’ crowd.
He might be right, but I have never myself encountered this kind of resistance to reason and evidence from the skeptic side of the global warming debate. Maybe Leif can provide us with a link.

How do you know that the raw isotope signature is a pretty good proxy for solar activity?
Other variables do need to be considered. Most obvious is the strength of the Earth's magnetic field. It's the combination of the Earth's magnetic field and the solar wind that deflects GCR.

Is it important to separate these two influences? Maybe not. Svensmark's theory is that it is the GCR that affects climate, and that the solar magnetic flux only affects climate indirectly, by blocking GCR. If he is correct then what matters is the combination of solar flux, the strength of the Earth's magnetic field, and the amount of GCR entering the solar system. We don't need to separate these influences from each other in order to test Svensmark's theory.

On the other hand, we would like to have an accurate measure of how much impact each of these variables has on climate, so we do ultimately want to parse out the separate records. Svensmark also thinks it is important to distinguish different energy levels for GCR. Both high and low energy GCR leave B10 isotope signatures, but Svensmark thinks that high energy GCR has the much stronger effect on climate.
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