Guest Post by Willis Eschenbach

I started out as a true believer that sunspots (or something that changes in sync with sunspots, like heliomagnetism, cosmic rays, solar wind, etc.) had a strong effect on the weather. When I was a kid I read that the great British astronomer William Hershel had said that British wheat prices were affected by the sunspot cycle. Made sense to me …

So when I started looking into the question, I figured it would be a piece of cake to find evidence supporting the connection … but nothing in climate science is simple. I started by looking into Hershel’s claim, and I was going to write it up … but then I found a scientific paper entitled “On the insignificance of Herschel’s sunspot correlation“. I hadn’t put much time into my research, and it was much better than my poor attempt. It clearly showed that Herschel was … well … not to put too fine a point on it, completely wrong.

Undaunted, I continued to look for correlations, and I’ve done so from time to time ever since. At this point I’ve looked in more than 20 places, and found no correlation. I append these studies at the end of this post.

Yesterday, a chance comment about sea surface temperature (SST) gave me a new thought about how to look for the signal. In general, I’ve looked at various time-series records of some parameter—river levels, lake levels, cloud amounts, volcanoes, and the like. I’ve analyzed them either with Fourier Analysis or CEEMD analysis.

Anyhow, the idea I had was to divide monthly gridded temperature datasets into months where the sunspots were higher than the median sunspot number for the period, and months where sunspots were lower than that media. Then, I’d subtract the gridcell-by-gridcell average of the low-sunspot months from that of the high-sunspot months. If the theory that low sunspot cycles were associated with low temperatures were true, I’d expect to find a positive difference between the two.

Since the original idea was about sea surface temperature (SST), I thought I’d start with that. The best gridded SST dataset I know of is the Reynolds OI dataset. It starts in 1981, and uses a mixture of satellite and surface data. From the NOAA site:

The NOAA 1/4° daily Optimum Interpolation Sea Surface Temperature (or daily OISST) is an analysis constructed by combining observations from different platforms (satellites, ships, buoys) on a regular global grid. A spatially complete SST map is produced by interpolating to fill in gaps.

It’s available here as a NetCDF document. Figure 1 shows the result of the analysis.

Figure 1. Average of high-sunspot-number months minus the average of low-sunspot-number months, Reynolds Optimally Interpolated Sea Surface Temperature. “High-sunspot” months averaged 135 sunspots; “low-sunspot” months averaged 26 sunspots.

As you can see, not only is the difference very tiny, it has the wrong sign. If low sunspot numbers actually lead to low temperatures, then high minus low should give a positive result. But in this case, it’s a negative result, and it’s only four-hundredths of one degree. In other words … no sign of sunspots affecting the SST.

Next, I thought I’d take a look at a global dataset. I used the Berkeley Earth gridded land and ocean data. I picked an arbitrary cutoff date of 1950, because observations before that start getting sparse. The data is available here as a NetCDF document. I did the same thing, dividing it into high-sunspot and low-sunspot months, and subtracted the low from the high. Figure 2 shows the results.

Figure 2. As in Figure 1, but with the Berkeley Earth global temperature data. Over this period, “High-sunspot” months averaged 155 sunspots; “low-sunspot” months averaged 33 sunspots.

Once again … same result. Wrong sign, tiny difference, no apparent effect of sunspots on the global temperature.

This finding is supported by a CEEMD analysis of the datasets. Here are the results for the Reynolds data:

You can see the sunspot peak (red line, Empirical Mode 6) at about 11.5 years. There’s nothing to match it in the Reynolds OI SST data. And here’s the corresponding chart for the Berkeley Earth data:

In this longer dataset, the sunspot period is 11 years, closer to the long-term average. And as with the Reynolds data, there is no 11-year cycle in the temperature records.

Conclusion? Once again, I’ve looked for a solar signal and found none.

Does this mean that the sunspot cycle doesn’t affect surface weather?

Nope. It just means that I haven’t been able to find one. Might be out there, but I’m up to 25 places or so that I’ve looked without finding it.

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12:32 AM here, my eyelids are drooping. Hang on, let me go outside … ah, great lungfuls of crisp air on a starry moonless night have me back in shape. Can’t hear the ocean, the wind is wrong. It’s 38°F, or 6°C, the forest is quiet, life is good. I’ll leave this here and come back to trim it up for publication in the morning.

11:30 AM, next morning. Sun is out, the tiny bit of the ocean I can see from our house is shining in the sunshine …

Ah, dear friends, what a world this is!

Best to all,

w.

PS: When you comment please quote the exact words you’re discussing, so we can all understand your subject.

FURTHER READING: Here are my previous posts on the subject.

Congenital Cyclomania Redux 2013-07-23

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Cycles Without The Mania 2013-07-29

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Splicing Clouds 2014-11-01

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My Thanks Apologies And Reply To Dr Nir Shaviv 2015-08-17

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