Hurricane Frequency And Sunspots

To be fair to the GCR theory there are two hypothesis.

Both start with high solar activity is correlated with low GCR activity which is then correlated with lower cloud response.

One hypothesis is that GCRs are more effective at seeding low level clouds which would cause cooling.

The other hypothesis is that GCRs are more effective at seeding high clouds which would cause warming.

Either way the evidence in general to support GCR modulation is weak since one hypothesis works pretty well prior to 1960 and breaks down after while the other works pretty well after 1960 but breaks down prior to that.

CERN also tested the general hypothesis of cloud seeding cosmic rays and could not demonstrate a significant effect either way.

Interestingly they were able to demonstrate a measurable cloud seeding effect from biogenic vapors. 

https://wattsupwiththat.com/2024/01/25/hurricane-frequency-and-sunspots/