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.