On the Surface Temperature Sensitivity of the Reflected Shortwave, Outgoing Longwave, and Net Incident Radiation

Abstract

he global-mean top-of-atmosphere incident solar radiation (ISR) minus the outgoing longwave radiation (OLR) and the reflected shortwave radiation (RSW) is the net incident radiation (NET). This study analyzes the global-mean NET sensitivity to a change in the global-mean surface temperature by applying the interannual anomaly correlation technique to 9 yr of Atmospheric Infrared Sounder (AIRS) global measurements of RSW and OLR under cloudy and clear conditions. The study finds the observed sensitivity of NET that includes the effects of clouds to be ?1.5 ± 0.25 (1σ) W m?2 K?1 and the clear NET sensitivity to be ?2.0 ± 0.2 (1σ) W m?2 K?1, consistent with previous work using Earth Radiation Budget Experiment and Clouds and the Earth?s Radiant Energy System data. The cloud effect, +0.5 ± 0.2 (1σ) W m?2 K?1, is a positive component of the NET sensitivity. The similarity of the NET sensitivities derived from forced and unforced models invites a comparison between the observed sensitivities and the effective sensitivities calculated for the Fourth Assessment Report models, although this requires some caution: The effective model sensitivities with clouds range from ?0.88 to ?1.64 W m?2 K?1, the clear NET sensitivity in the models ranges from ?2.32 to ?1.73 W m?2 K?1, and the cloud forcing sensitivities range from +0.14 to +1.18 W m?2 K?1. The effective NET and clear NET sensitivities derived from the models are statistically consistent with those derived from the AIRS data, considering the observational and model derivation uncertainties.