Guest Post by Willis Eschenbach [See Update At End]
In a recent post, Anthony published Leif Svalgaard’s new paper showing 9,000 years of reconstructed solar activity.
In the discussion, someone pointed out that the “Maunder Minimum”, a time of very low solar activity, corresponds with the coldest decade in a long-term reconstruction of summer temperatures in Scotland. Their temperature reconstruction is based on a group of pine tree-ring records spanning 800 years. Their graph is shown below:
As you can see, the period around 1690 is extremely cold. This was put forward as support for the idea that sunspot cycles affect the temperature. The idea is that when sunspots are low, temperatures are low as well. And the year 1690 is during the Maunder Minimum, a time of low sunspots.
However, as you may know if you follow my work, I like to take the largest look at the longest data that I can find. So rather than build a theory based on one decade of cold temperatures lining up with one sunspot minimum, I decided to compare the two graphs shown above. I first “standardized” both datasets, meaning that I set each of their averages to zero and each of their standard deviations to one. That allows us to compare them directly. Here is that result:
Now, the commenter was indeed correct that the low temperature in 1690 was during the Maunder Minimum.
However, the other minima do not line up with much of anything. The Wolf Minimum occurred during not just a warm period, but during the warmest period in the record. Similarly, the Sporer Minimum occurred during the warm period just before the drop to the “Little Ice Age” of the 1600s.
Then we have the Maunder Minimum. Temperatures started dropping about 150 years before the start of the Maunder Minimum, and during the first hundred years of dropping temperatures the sunspots were increasing. So obviously, the sun was not the cause of the drop in temperature.
Next, although the Dalton minimum occurred during a cold period. temperatures started dropping some seventy years or so before the start of the Dalton minimum … and temperatures warmed from the start to the end of the Dalton Minimum.
Finally, in recent times, you can see that sunspots started decreasing about 1980, while temperatures have risen during that time.
I leave the reader to draw the obvious conclusions regarding sunspots and Scottish temperatures …
[UPDATE] Some folks in the comments have said that the Scottish pine series is just as bad as many of the other tree ring series, such as those abysmal creations of Michael Mann et ilk …
However, this doesn’t appear to be the case, viz:
So while it is true in general that trees are not thermometers … when handled properly, they do appear to do a reasonable job of recording thermal variations.
PS—When you comment, please quote the exact words that you are referring to, so that we can all understand what you are discussing.