I am reposting David Archibald’s post, but I recommend that readers look at the comments. As expected Leif Lsvalgaard does not agree, but he provides some useful information. I found most of thoughtful comments to be interesting.
Guest essay by David Archibald
Two useful things we would like to know are the length of Solar Cycle 24 and the amplitude of Solar Cycle 25. Figure 1 below shows the NOAA version of Solar Cycle 24 progression with the 23/24 transition copied onto the end of their projection. This crude method (we don’t have another) suggests that the 24/25 transition will be at the end of 2021 which would make Solar Cycle 24 twelve years long. Solar physicists have generally given up forecasting Solar Cycle 25 amplitude. The only extant forecast is Livingstone and Penn’s forecast of an amplitude of seven. In the bigger picture, almost a decade after Schatten and Tobiska forecast a return to a Maunder Minimum-like level of activity, another solar physicist, Mark Giampapa of the National Solar Observatory in Tuscon, Arizona, is of the opinion that “we are heading into a Maunder Minimum” that…
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The Next Grand Minimum 