Although the sun provides nearly all the energy needed to warm the planet, its contribution to climate change remains widely questioned. Many empirically based studies claim that it has a significant effect on climate, while others (often based on computer global climate simulations) claim that it has a small effect.
The Intergovernmental Panel on Climate Change (IPCC) supports the latter view and estimates that almost 100% of the observed warming of the Earth's surface from 1850–1900 to 2020 was caused by man-made emissions. This is known as the anthropogenic global warming (AGWT) theory.
It is important to notice that the AGWT is based solely on computer simulations of global climate models (GCMs) that use total solar irradiance (TSI) records with very low multidecadal and long-term variability.
The total sun's effect on the climate cannot be assessed using only the TSI forcing functions because, for example, alternative solar-related mechanisms have been claimed to directly modulate cloud cover.
This result suggests that about 80% of the solar influence on the climate may not be induced by TSI forcing alone, but rather by other sun-climate processes (e.g., by a solar magnetic modulation of cosmic ray and other particle fluxes, and/or others). These alternative mechanisms must be thoroughly investigated and physically understood before trustworthy GCMs can be created to correctly interpret climate change and produce reliable climate change projections for the future.
