Science Source

Attribution of the present‐day total greenhouse effect

States that the relative contributions of atmospheric long‐wave absorbers to the present‐day global greenhouse effect are among the most misquoted statistics in public discussions of climate change
States that much of the interest in these values is however due to an implicit assumption that these contributions are directly relevant for the question of climate sensitivity
Reviews the existing literature and uses the Goddard Institute for Space Studies ModelE radiation module to provide an overview of the role of each absorber at the present‐day and under doubled CO2
Finds that water vapor is the dominant contributor (∼50% of the effect), followed by clouds (∼25%) and then CO2 with ∼20%
Finds that all other absorbers play only minor roles
Finds that in a doubled CO2 scenario, this allocation is essentially unchanged, even though the magnitude of the total greenhouse effect is significantly larger than the initial radiative forcing, underscoring the importance of feedbacks from water vapor and clouds to climate sensitivity