An Analytic Model for the Clear-Sky Longwave Feedback

Abstract Climate models and observations robustly agree that Earth’s clear-sky longwave feedback has a value of about −2 W m K −1 , suggesting this can be estimated from first principles. In study, we derive an analytic model for feedback. Our approach uses novel spectral decomposition splits the into four components: surface Planck three atmospheric feedbacks CO 2 H O, O continuum. We obtain expressions each these terms, also framed in terms Simpson’s law deviations therefrom. validate by comparing it against line-by-line radiative transfer calculations across wide range climates. Additionally, qualitatively matches spatial maps comprehensive climate model. For present-day Earth, our analysis shows is dominated global mean dry subtropics; meanwhile, become important inner tropics. Together, results show view elucidates not only its global-mean magnitude, but pattern state dependence past future Significance Statement The determines how much planet warms due to changes forcing. more than 50 years scientists have been predicting using complex numerical models. Except cloud effects largely agree, lending confidence warming predictions, nobody yet derived simpler considerations. pen paper. confirm get right number reasons, allow us explain regional variations These are difficult understand solely crucial