Spectroscopic measurements at top-of-atmosphere are uniquely capable of
attributing changes in Earth’s outgoing infrared radiation field to
specific greenhouse gasses. The Atmospheric Infrared Sounder (AIRS)
placed in orbit in 2002 has spectroscopically resolved a portion of
Earth’s outgoing longwave radiation for 17 years. Concurrently,
atmospheric CO₂ rose from 373 to 410 ppm, or 28% of the total increase
over pre-industrial levels. The IPCC Fifth Assessment Report predicted
0.508±0.102 Wm⁻² additional radiative forcing from this CO₂ increase.
Here it is shown that global measurements under nighttime, cloud-clear
conditions reveal 0.358±0.067 Wm⁻² of CO₂-induced radiative forcing, or
70% of IPCC model predictions.