• solar irradiance;
  • solar variability;
  • climate variability;
  • global climate models

[1] Radiation from the Sun is the dominant source of energy input to the Earth's climate system; even small variations in solar irradiance can produce noticeable climate changes on global and regional scales. Determining how much of the observed global change can be attributed to variations in the Sun's output and how much can be attributed to human or other influences requires an accurate record of solar irradiance. Measurements of solar irradiance made by the Total Irradiance Monitor (TIM) on NASA's Solar Radiation and Climate Experiment (SORCE) satellite give a value of total solar irradiance that is significantly lower than previously accepted values. Kopp and Lean show that this new, lower value is more accurate than measurements made using older instruments. They used laboratory studies and satellite calibrations to diagnose and quantify error sources on TIM and other space-based solar radiometers and found that earlier radiometers measured higher values of solar irradiance because they included scattered instrument light in their signals, while the different optical design of the TIM radiometer reduces this spurious signal and acquires more accurate measurements. They also show that TIM's high stability gives improved agreement with models estimating solar variability, concluding that this new instrument provides the most accurate value of solar irradiance and helps improve estimates of the Sun's influence on climate. (Geophysical Research Letters, doi:10.1029/2010GL045777, 2011)