Sun-like stars shed light on solar climate forcing

This compares with the +2.2 1.1 W m(-2) IPCC estimate for anthropogenic forcing. Three critical assumptions are made.

In decreasing order of importance they are: (a) most of the brightness variations occur within the average time series length of 17 yr; (b) the Sun seen from the ecliptic behaves as an ensemble of middle-aged solar-like stars; and (c) narrowband photometry in the Stromgren b and y bands are linearly proportional to the total solar irradiance. Assumption (a) can best be relaxed and tested by obtaining more photometric data of Sun-like stars, especially those already observed.