Satellite observations since 1978 have shown the sun’s total irradiance changed by no more than 0.1% over solar cycles 21-23. However, observations of sunspot numbers, the concentrations of cosmogenic isotopes and sunlike stars suggest that the sun’s irradiance may have increased by 0.3% from the 17th to the 20th century. A simple climate model used to determine the climate sensitivity, δT 2x-the change in global near-surface temperature resulting from doubling the pre-industrial CO2 concentration-by replicating the observed changes of hemisphericmean temperatures since 1856 has shown that δT2X is nearly halved if the sun’s irradiance changed before 1978 as constructed from “surrogate” data. Thus, in terms of future anthropogenic climate change impacts and policy it is important to determine whether the sun changed climate. To do so, fingerprint detection studies have been performed with coupled atmosphere/ocean general circulation models (A/O GCMs) to detect the geographical pattern of solar-induced temperature change. Successive studies performed at the Max-Planck Institute for Meteorology and the Hadley Centre for Climate Research and Prediction have increasingly concluded that the sun did change climate during the first half of the twentieth century. However, these detection studies did not use spectrally dependent changes in solar irradiation. Other GCM studies using the change in solar ultraviolet observed during solar cycle 22 and constructed from 1610 to the present have shown significant changes in near-surface temperature resulting from changes in stratospheric ozone, temperature and wind. Thus it is now time to perform fingerprint detection studies with A/0 GCMs that include spectrally dependent solar irradiance variations and comprehensive interactive photochemistry.