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Observations of thermospheric infrared radiative cooling by carbon dioxide (CO2) and nitric oxide (NO) from 2002 to 2018 are presented. The time span covers more than 6,000 days including most of solar cycle (SC) 23 and the entirety of SC 24 to date. Maxima of infrared cooling rate profiles (nW/m(3)) are smaller during SC 24 than SC 23, indicating a cooler thermosphere. Rates of global infrared power (W) from CO2 are now at levels observed during the deep solar minimum of 2009. Rates of NO power are still larger than those observed during 2009 and are being maintained at an elevated level by geomagnetic activity. During SC 24 to date, the thermosphere has radiated 70% of the energy of the mean of the past five cycles and would require an additional 1,690 days at current infrared radiation rates to reach that amount.

Plain Language Summary Sixteen years of observations of infrared radiation emitted by nitric oxide and carbon dioxide molecules in Earth's atmosphere above 100 km are presented. The infrared emission intensity changes with time due to variability in the amount of ultraviolet radiation from the Sun and also to variations in the solar wind. The infrared emissions regulate the temperature and density of the atmosphere above 100 km. The observations presented here provide the first comparison of the effects of two different 11-year solar cycles over which time the solar ultraviolet and solar wind output have varied dramatically. The infrared radiation is a measure of the pulse of the Sun in the atmosphere of the Earth. Current infrared radiation levels above 100 km are nearly at the levels observed 9 years ago during the last solar minimum. These data offer the first-ever comparison of the effects of two very different solar cycles on a fundamental property of the atmosphere.