spacecraft have measured the total solar irradiance since the late 1970s. There is an 11-year cycle in total solar irradiance of peak-to-peak amplitude ~1 W m−2 (0.1 percent) in the past three cycles. Allowing for reflection of 30 percent of this incident energy (Earth’s albedo) and averaging over the globe, the corresponding climate forcing is of order 0.2 W m−2.
Multiple TSI datasets have been combined into a composite time series of daily total solar irradiance from 1979 to the present. This requires the cross-calibration of measurements made by overlapping datasets to adjust