Reconstruction of solar spectral irradiance since the Maunder 1 minimum

Solar irradiance is the main external driver of the Earth’s climate. Whereas the 3 total solar irradiance is the main source of energy input into the climate system, solar UV ir4 radiance exerts control over chemical and physical processes in the Earth’s upper atmosphere. 5 The time series of accurate irradiance measurements are, however, relatively short and limit 6 the assessment of the solar contribution to the climate change. Here we reconstruct solar to7 tal and spectral irradiance in the range 115–160 000 nm since 1610. The evolution of the so8 lar photospheric magnetic flux, which is a central input to the model, is appraised from the 9 historical record of the sunspot number using a simple, but consistent physical model. The model 10 predicts an increase of 1.25 W/m, or about 0.09%, in the 11-yr averaged solar total irradi11 ance since the Maunder minimum. Also, irradiance in individual spectral intervals has gener12 ally increased during the last 4 centuries, the magnitude of the trend being higher towards shorter 13 wavelengths. In particular, the 11-yr averaged Ly-α irradiance has increased by almost 50%. 14 An exception is the spectral interval between about 1500 and 2500 nm, where irradiance has 15 slightly decreased (by about 0.02%). 16