Empirical assessment of the role of the Sun in climate change using balanced multi-proxy solar records
https://www.sciencedirect.com/science/article/pii/S1674987123001172• Factors other than direct TSI forcing account for around 80% of the solar influence on the climate.
• Important solar-climate mechanisms to be investigated before developing reliable GCMs.
...empirical studies often found that the solar contribution to climate changes throughout the Holocene has been significant, whereas GCM-based studies, which only adopt radiative forcings, suggest that the Sun plays a relatively modest role.
The CMIP6 GCMs appear to greatly underestimate the Sun’s role in climate change because of two major limitations: erroneous solar forcings have likely been integrated into the models; and TSI alone appears to likely be not the most important solar forcing. Additional solar-magnetism related forcings and associated mechanisms are not included in the GCMs because they are currently poorly understood, despite the fact that there are several empirical indications that they might sufficiently modulate the cloud cover system (by 5% or less) to explain a significant component of the observed climatic changes.
At least about 80% of the solar influence on the climate could be generated by processes other than direct TSI forcing. If this result is correct, several solar-climate mechanisms must be thoroughly investigated and fully understood before reliable GCMs can be developed.