Early Measurements of the Role of Clouds in the Radiation Balance

Early estimates of the effect of clouds on Earth’s energy balance were made using data from NOAA satellite observations designed to detect the presence of clouds, but not their energetic effects.  Regression procedures were used to estimate broadband irradiance from narrowband radiances.  These early works revealed the complexity of cloud radiative effects and their dependence on cloud type.  The strong leverage of marine boundary layer clouds on Earth’s energy balance and the near neutrality of tropical convective clouds were noted early on.  Later, broadband instruments with better calibration were developed.  Cavity radiometers connected to telescopes allowed the radiation balance to be measured at high spatial resolution, from which the irradiance from clear scenes could be estimated.  The difference between the average and clear-sky energy balance became the measurement of what was first called cloud forcing, but later defined to be the cloud radiative effect on Earth’s energy balance.  These measurements formed a strong constraint on climate change theory and on the validation of climate models.