Greenhouse Gas Forcing and Climate Feedback Signatures Identified in Hyperspectral Infrared Satellite Observations

Abstract

Global greenhouse gas forcing and feedbacks are the primary causes of climate change but have limited direct observations. Here we show that continuous, stable, global, hyperspectral infrared satellite measurements (2003–2021) display decreases in outgoing longwave radiation (OLR) in the CO2, CH4, and N2O absorption bands and increases in OLR in the window band and H2O absorption bands. By conducting global line-by-line radiative transfer simulations with 2003–2021 meteorological conditions, we show that increases in CO2, CH4, and N2O concentrations caused an instantaneous radiative forcing and stratospheric cooling adjustment that decreased OLR. The climate response, comprising surface and atmospheric feedbacks to radiative forcings and unforced variability, increased OLR. The spectral trends predicted by our climate change experiments using our general circulation model identify three bedrock principles of the physics of climate change in the satellite record: an increasing greenhouse effect, stratospheric cooling, and surface-tropospheric warming.Plain Language SummaryGreenhouse gas emissions from human activities trap heat (radiative forcing) and cause global warming and climate change. Observing the global radiative forcing caused by well-mixed greenhouse gases has been elusive because of irregular, uncalibrated, or limited areal measurements. However, the Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua Satellite has recently provided the requisite data (2003–2021). These unprecedented observations provide measurements of Earth’s emitted thermal heat at fine-scale wavelengths, that is, the infrared spectrum, allowing us to pinpoint the effect of greenhouse gas concentration increases on Earth’s climate. We find large increases in the heat trapped by CO2, CH4, and N2O. Directly monitoring the heat impact of these gases is therefore now possible. In response to this forcing, we found that the planet warmed and emitted extra heat to space via the water vapor absorption sections and transparent sections of the infrared spectrum. Our study therefore provides a strong validation of the physical basis for climate change.Key PointsDirect monitoring of the radiative impact of greenhouse gas changes is now possible through hyperspectral infrared satellite observationsObserved spectral trends include the signatures of an increasing greenhouse effect, stratospheric cooling, and surface-tropospheric warmingMagnitude of forcing over 2003–2021 found to be consistent with the latest Intergovernmental Panel on Climate Change estimate