Dependence of Earth's Thermal Radiation on Five Most Abundant Greenhouse Gases

W. A. van Wijngaarden; W. Happer

paper

Dependence of Earth's Thermal Radiation on Five Most Abundant Greenhouse Gases

arXiv:2006.03098

Abstract

The atmospheric temperatures and concentrations of Earth's five most important, greenhouse gases, H $_{2}$ O, CO $_{2}$ , O $_{3}$ , N $_{2}$ O and CH $_{4}$ control the cloud-free, thermal radiative flux from the Earth to outer space. Over 1/3 million lines having strengths as low as $1 0^{- 27}$ cm of the HITRAN database were used to evaluate the dependence of the forcing on the gas concentrations. For a hypothetical, optically thin atmosphere, where there is negligible saturation of the absorption bands, or interference of one type of greenhouse gas with others, the per-molecule forcings are of order $1 0^{- 22}$ W for H $_{2}$ O, CO $_{2}$ , O $_{3}$ , N $_{2}$ O and CH $_{4}$ . For current atmospheric concentrations, the per-molecule forcings of the abundant greenhouse gases H $_{2}$ O and CO $_{2}$ are suppressed by four orders of magnitude. The forcings of the less abundant greenhouse gases, O $_{3}$ , N $_{2}$ O and CH $_{4}$ , are also suppressed, but much less so. For current concentrations, the per-molecule forcings are two to three orders of magnitude greater for O $_{3}$ , N $_{2}$ O and CH $_{4}$ , than those of H $_{2}$ O or CO $_{2}$ . Doubling the current concentrations of CO $_{2}$ , N $_{2}$ O or CH $_{4}$ increases the forcings by a few per cent. These forcing results are close to previously published values even though the calculations did not utilize either a CO $_{2}$ or H $_{2}$ O continuum. The change in surface temperature due to CO $_{2}$ doubling is estimated taking into account radiative-convective equilibrium of the atmosphere as well as water feedback for the cases of fixed absolute and relative humidities as well as the effect of using a pseudoadiabatic lapse rate to model the troposphere temperature. Satellite spectral measurements at various latitudes are in excellent quantitative agreement with modelled intensities.

This manuscript has 38 pages containing 15 figures

Dependence of Earth's Thermal Radiation on Five Most Abundant Greenhouse Gases

Abstract

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