Landscheidt 5 (Review of Eddy’s “The Case of the Missing Sunspots”)
Posted by The Diatribe Guy on June 13, 2008
The last post I made on this topic was a summary overview of the Eddy paper, “The Maunder Minimum.” For a review of all the posts on this topic, click here.
The reason I am summarizing the Eddy papers is because Landscheidt refers to them in the paper I’m reviewing. What better way to discuss and explain Landscheidt’s paper than to understand the sources he is drawing from? And so, I move to the second Eddy paper, which appeared in Scientific American in 1977, volume 236, issue 5, pages 80-92. Thanks to the local University library and its microfilm collection, I was able to track it down. My summary follows:
Comparison to the 1976 paper
This paper is in large part a repackaging of the 1976 paper in many ways. In my opinion, each has their merits, but as a general overview this one seemed to be a little better presented. I won’t re-hash the points made from the first paper that were already summarized. Basically, he starts again with a historical look at E. Walter Maunder’s and Gustav Spoerer’s look into the Maunder Minimum. He then discusses the ability of the astronomers in those days to view and record sunspots. He more or less gives the same story on the evidence already discussed: the record of naked-eye sunspots, the record of aurorae observations, the descriptions from full solar eclipses, sunspot counts recorded, and the like.
However, in this paper, Eddy does provide a few additional insights into investigation into solar activity and the Maunder Minimum, as well as connection to climate. I will only cover those points that are new in relation to his other paper.
Some Additional Points About the Known Evidence
In my last summary, I noted that the jump in the recorded sightings of auroras coming out of the Maunder Minimum indicated the absence during the Maunder, especially given the recorded presence in the 70 years prior to the Maunder Minimum. Eddy still holds this to be a solid conclusion, but he does point out that, in part, the jump has a social element to it, as well. As people became more aware of their presence, they were more widely noticed and written about. This doesn’t change the conclusion, but I wanted to point out that caveat.
Another clue that Eddy discusses that was not found in “The Maunder Minimum” is his work (with Dorothy Trotter and Peter Gilman) on reconstructing the sun’s rotation patterns in the 17th century. Currently, the sun rotates once every 27 days at the equator (as viewed from earth – the actual rotation is around 25 days – the difference is due to the earth’s revolution around the sun in order to see something in the same relative spot), and increases as you move closer to the poles. This “differential rotation” lends itself to the theory of a dynamo effect that gives rise to sunspot activity through the interaction of deep-seated magnetic fields in the sun and its surface. A change in the rotation of the sun would change this interaction.
By use of two old books: Rosa Ursina by Christoph Scheiner in 1630 and Selenographia by Johannes Hevelius in 1647, solar rotation could be estimated. Each book presented daily drawings of the sun nearly continuously for two years. Scheiner’s drawings were in 1625 and 1626. This book demonstrated a rotation similar to today. Hevelius’ drawings from 1642-1644 show a significant change. The equatorial rotation sped up by a full day. The poles sped up slightly, but not in proportion to the equatorial change. Eddy questions whether or not a change in the sun that provides a faster rotation is the perpetrator of the Maunder Minimum.
Eddy discussed Carbon-14 levels in the other paper, but there are a few additional observations made here. The carbon 14 found in the air that is created by galactic cosmic rays finds its way into tree rings on a 40 year lag or so. Analysis can be done on the ratio of Carbon 14 to the common isotope. But Eddy extends this analysis in this paper by looking into the analysis of the rings of the bristlecone pine, the oldest living thing on earth.
Extended Analysis of Carbon 14 Levels
The record now extends back to 5000 B.C. The modulation previously discussed due to the 10,000 year period of earth’s magnetism can be seen more clearly. The evidence allowed a calibration of the carbon 14 record to solar changes.
At least 12 incidents in one direction or another have occurred that are at least as prominent as the Maunder Minimum, in the last 5000 years. Each lasts from 50 to several hundred years. The first predecessor to the Maunder Minimum is the Spoerer Minimum, from about 1400 to 1510. The Medieval Maximum occurred between 1100 and 1300, linked with anomalously high solar activity.
What About Now?
Eddy suggests that there has been continuous increases in solar activity since the Maunder Minimum, and even anomalously so. He bases this not only on the low anomaly of C-14 in modern times, but in the other observations of aurora, sunspot counts, the well-defined corona. But he does have a large caveat with the Carbon-14 measure that I only briefly alluded to in the other summary. The “Suess Effect” which says that to the extent that fossil fuel production introduces isotopes other than Carbon 14 into the atmosphere, it dilutes the C-14 concentration. So, Eddy cautions about using the C-14 as a measure for solar activity, but based on the observations, it does appear that some portion of the current negative anomaly is due to solar activity, and we are in a period of anomalously high activity.
The Climate Connection
Possibly the most relevant point to come out of the new paper is Eddy’s ability to connect historical long-term climate conditions to the solar activity, or lack thereof. We have records of advancing glaciers and colder climate during the Maunder Minimum, but that could have been coincidental. But now with the radiocarbon dating extending back thousands of years, and multiple periods of C-14 anomalies, more investigation could be done. There are historical records where climate conditions of different periods are recorded, as well as the ability to determine and date the extent of glaciation in those different time periods. Comparing these records produced an undeniable pattern, that Eddy describes as “a key in a lock.” Every extended decrease in solar activity matches a period of glacial advance, while every extended increase in activity matches a period of glacial retreat. As records allow, the long-term temperatures match perfectly as well, as does winter severity indexes.
Eddy draws one interesting conclusion, however: the link seems to be for periods of 50 years or more of anomalous activity. This study reveals little about short-term affects on weather during an 11-year sunspot cycle. This is an important consideration when discussing the impact of the sun, as I have heard suggestions that the sun must not drive temperature, since it was at minimum in 2007 and it was hot in 2007. Eddy here is looking at the longer-term envelope of peaks and valleys in the cycles.
I wanted to end with a comment in Eddy’s paper that I believe is entirely appropriate in today’s scientific arena.
It would seem that Maunder and Spoerer were right and that most of the rest of us have been wrong. As is often the case in the onrush of modern science, we had too quickly forgotten the past, forgotten the less-than-perfect pedigree of the sunspot cycle and the fact that it too once came as a surprise. We had adopted a kind of solar uniformitarianism, contending that the modern behavior of the sun represented the normal behavior of the sun over a much longer span of time.
It would seem quite possible that, in our current onrush to show a link between Carbon Dioxide and climate change, that we are, as well, too easily forgetting the past.