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Quantifying the Drivers of the Clear Sky Greenhouse Effect, 2000–2016
Author(s) -
Raghuraman Shiv Priyam,
Paynter David,
Ramaswamy V.
Publication year - 2019
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2019jd031017
Subject(s) - troposphere , environmental science , sky , atmospheric sciences , water vapor , longwave , atmosphere (unit) , earth's energy budget , climatology , energy balance , relative humidity , greenhouse effect , mean radiant temperature , radiative transfer , climate change , meteorology , global warming , radiation , physics , geology , oceanography , quantum mechanics , thermodynamics
The clear sky greenhouse effect ( G ) is defined as the trapping of infrared radiation by the atmosphere in the absence of clouds. The magnitude and variability of G is an important element in the understanding of Earth's energy balance; yet the quantification of the governing factors of G is poor. The global mean G averaged over 2000 to 2016 is 130–133 W m −2 across data sets. We use satellite observations from Clouds and the Earth's Radiant Energy System Energy Balance and Filled (CERES EBAF) to calculate the monthly anomalies in the clear sky greenhouse effect (Δ G ). We quantify the contributions to Δ G due to changes in surface temperature, atmospheric temperature, and water vapor by performing partial radiation perturbation experiments using ERA‐Interim and Geophysical Fluid Dynamics Laboratory's Atmospheric Model 4.0 climatological data. Water vapor in the middle troposphere and upper troposphere is found to contribute equally to the global mean and tropical mean Δ G . Holding relative humidity (RH) fixed in the radiative transfer calculations captures the temporal variability of global mean Δ G while variations in RH control the regional Δ G signal. The variations in RH are found to help generate the clear sky super greenhouse effect (SGE). Thirty‐six percent of Earth's area exhibits SGE, and this disproportionately contributes to 70% of the globally averaged magnitude of Δ G . In the global mean, G's sensitivity to surface temperature is 3.1–4.0 W m −2 K −1 , and the clear sky longwave feedback parameter is 1.5–2.0 W m −2 K −1 . Observations from CERES EBAF lie at the more sensitive ends of these ranges and the spread arises from its cloud removal treatment, suggesting that it is difficult to constrain clear sky feedbacks.