NASA data on upper atmosphere cooling resurfaces

NASA’s resurfaced upper-atmosphere graphic points to an old finding, not a new discovery. A 2021 NASA article said combined observations from three agency satellites showed the mesosphere — about 30 to 50 miles above Earth’s surface — has been cooling and contracting as greenhouse gas concentrations rise. The post drew fresh attention on X over the past two days, but the underlying claim comes from archival NASA material and long-running satellite records. NASA said at the time that scientists had “long predicted” the effect in the upper atmosphere, but needed decades of observations to separate it from solar-cycle and other variability. (nasa.gov) ### Which part of the atmosphere is NASA talking about? NASA’s 2021 write-up focused on the mesosphere, not the air near the ground where people experience surface warming. The agency described that layer as roughly 30 to 50 miles above Earth and said the long-term record was assembled from three satellites. NASA’s SABER instrument team has also described related behavior higher up. (nasa.gov) A December 2021 NASA article on the TIMED satellite said carbon dioxide “leads to cooling in the upper atmosphere and a decrease in density at altitudes up to 1,000 km,” affecting the mesosphere and lower thermosphere. ### How can greenhouse gases warm the lower atmosphere but cool the upper one? (nasa.gov) James Russell, a Hampton University atmospheric scientist and co-author cited by NASA, said the lower atmosphere behaves more like a thick insulating layer because molecules are packed closely together. In that denser air, heat is more easily trapped and transferred. (nasa.gov) NASA said the upper atmosphere is much thinner, so carbon dioxide behaves differently there. Because molecules are farther apart, the agency said heat captured by carbon dioxide is more readily emitted to space before it is reabsorbed, producing cooling rather than the surface-level warming associated with greenhouse gases in the troposphere. (nasa.gov) ### What numbers did NASA actually report? Scott Bailey of Virginia Tech, the lead of the 2021 study cited by NASA, said researchers had to combine “three satellites’ worth of data” to build a record long enough to measure the trend. NASA said those observations covered about 30 years. NASA reported that the summer mesosphere over Earth’s poles was cooling by 4 to 5 degrees Fahrenheit and contracting by 500 to 650 feet per decade. (nasa.gov) The agency added that, without changes in human carbon dioxide emissions, the rates were expected to continue. ### Does newer research still support the mechanism? A 2025 paper in the Journal of Geophysical Research: Atmospheres examined thermospheric infrared power measured by the SABER instrument from 2002 through 2023. (nasa.gov) The authors, including researchers from NASA Langley Research Center, wrote that the thermosphere had cooled for more than two decades because of increasing carbon dioxide while still radiating a roughly constant amount of energy after accounting for natural variability. That paper addressed the thermosphere rather than the exact mesospheric trend highlighted in the 2021 NASA article. But the authors said their results “validate the mechanism of thermospheric greenhouse cooling,” reinforcing the broader agency explanation now recirculating online. ### Why does NASA say the contraction matters? NASA’s December 2021 SABER overview said lower density in the upper atmosphere matters for satellites and debris in low Earth orbit because atmospheric drag falls as the air thins. (agupubs.onlinelibrary.wiley.com) The agency said that has implications for collision risk assessments as satellite numbers rise. NASA’s continuing public record on the topic remains tied to SABER on the TIMED spacecraft, which the agency said in 2021 was still collecting data two decades after launch. The most current peer-reviewed update surfaced in the 2025 thermosphere paper using SABER measurements through 2023. (nasa.gov)