10 Aug 2023
 | 10 Aug 2023

Direct Observational Evidence from Space of the Effect of CO2 Increase on Longwave Spectral Radiances: The Unique Role of High Spectral Resolution Measurements

Joao Teixeira, Robert C. Wilson, and Heidar T. Thrastarson

Abstract. We present a direct measurement of the impact of increased atmospheric CO2 on the spectra of Earth's longwave radiation obtained from space. The goal of this study is to experimentally confirm that the direct effects of CO2 increase on the Earth’s outgoing longwave spectra follow theoretical estimates, by developing a methodology that allows for a direct and more precise comparison between theory and observations. In this methodology, a search is performed to find selected ensembles of observed atmospheric vertical profiles of temperature and water vapor that are as close as possible to each other in terms of their values. By analysing the spectral radiances measured from space by the Atmospheric Infrared Sounder (AIRS), corresponding to the selected ensembles of profiles, the effects of increased CO2 on the spectra can be isolated from the temperature and water vapor effects. The results illustrate the impact of the increase of CO2 on the longwave spectra and compare well with theoretical estimates. As far as the authors are aware, this is the first time that the spectral signature of the increase of CO2 (isolated from temperature and water vapor changes) has been directly observed from space.

Joao Teixeira et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-924', Anonymous Referee #1, 12 Sep 2023
  • RC2: 'Comment on egusphere-2023-924', Anonymous Referee #2, 04 Oct 2023

Joao Teixeira et al.

Data sets

AIRS/Aqua L1B Infrared (IR) geolocated and calibrated radiances V005 AIRS Project

AIRS/Aqua L2 Standard Physical Retrieval (AIRS+AMSU) V006 AIRS Science Team

Model code and software

kCARTA L. Strow, S. DeSouza-Machado, H. Motteler and S. Hannon

Joao Teixeira et al.


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Short summary
This paper presents direct evidence from space (solely based on observations) that CO2 increase leads to the theoretically expected effect on longwave spectral radiances. This is achieved by using a methodology that allows to isolate the CO2 effects from the temperature and water vapor effects. By searching for ensembles of temperature and water vapor profiles that are similar to each other, but have different values of CO2, it is possible to estimate the direct effects of CO2 on the spectra.