Current and Future Changes in Earth's Outgoing Infrared Spectrum

Abstract Hyperspectral infrared satellite observations provide an information‐rich, global record of climate mean state and change without the structural uncertainties often present satellite retrievals and reanalyses. Current and planned hyperspectral satellite missions will continuously observe changes in Earth's outgoing infrared spectrum into the 2040s. Here, we study current and future changes in the infrared spectrum using 22 years of observations from the NASA AIRS instrument and 40 years of AIRS‐like observations simulated in an Earth System Model. Currently detectable changes are dominated by forcing and surface warming. Conversely, trends in spectral channels where and water vapor forcing respectively oppose forced stratospheric and tropospheric temperature responses are indistinguishable from observed internal variability. By the early 2040s, however, mid‐latitude stratospheric cooling and tropospheric warming outcompete greenhouse gas forcing to produce significant trends of opposing signs. Detecting these trends requires that the total uncertainty of a multi‐instrument, intercalibrated record is below 0.02 K/yr.