Sunspots [image credit: NASA]

Wikipedia’s Solar activity and climate web page says:
Solar activity has been on a declining trend since the 1960s, as indicated by solar cycles 19-24, in which the maximum number of sunspots were 201, 111, 165, 159, 121 and 82, respectively.

We’re probably not surprised that they prefer a metric which appears to support their often-expressed view in various climate-related pages that modern global warming can’t be natural.

But is the sunspot maximum the most relevant metric to judge the level of solar activity by? Another Wikipedia page is its List of Solar Cycles.

It has various stats on the known cycles, one of which is ‘Average spots per day’. There’s no data shown before SC 10, but that’s good enough as it started in 1855, roughly when modern warming is thought to have originated.

Based on the Gnevyshev-Ohl rule, which Wikipedia says ‘is an empirical rule according to which the sum of Wolf’s sunspot numbers over an odd cycle exceeds that of the preceding even cycle’, we’ll obtain the ‘average spots per day’ figures of solar cycles 10+11, 12+13, 14+15 etc. and check the results, giving a ranking ().

10+11 = 181/2 (4)
12+13 = 122/2 (7)
14+15 = 127/2 (6)
16+17 = 164/2 (5)
18+19 = 238/2 (1)
20+21 = 197/2 (2)
22+23 = 188/2 (3)
[24+25 = 49 + ?(unknown as cycle 25 only recently started)]

According to this list, the three most active sunspot cycles since 1855 were between 1944 and 2008 (solar cycles 18-23). So is it true to say ‘solar activity has been on a declining trend since the 1960s’, or is it perhaps an attempt to downplay the role of the sun in climate?

It’s not a coincidence that recent cycles have mostly been of shorter duration than the ~11 year average. The data point to greater sunspot intensity in such cycles, as a rule of thumb.
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Re the Gnevyshev-Ohl rule, Wikipedia points out: ‘The rule breaks down under certain conditions.’ The only example in our list is for cycles 22 and 23, the previous breach being for cycles 8 and 9 (see List of Solar Cycles).

via Tallbloke’s Talkshop

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December 5, 2020 at 03:54AM