Radiometry from the Solar Maximum Mission and Nimbus 7 satellites has demonstrated that the solar constant varies at a peak‐to‐peak level of up to 0.2% on time scales of weeks. The rotation and evolution of dark spots and bright faculae across the sun's disc accounts for most of that variation. Reasonable explanations have been put forward to explain how the spot‐blocked heat flow might be stored and to explain the source of the intense radiation that gives rise to the increased irradiance produced by the bright magnetic faculae. Time‐dependent models of the response of the solar convection zone to small perturbations also indicate that slower variations in total solar irradiance of comparable magnitude are likely. More precise observations of the total solar irradiance and radius over long time scales are required to demonstrate the existence of such climatologically relevant changes and to test models that would enable us to interpret and, possibly, to predict these