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A New Study Explains How Carbon Dioxide Cools the Upper Atmosphere--and Warms Earth Below
by Columbia Climate School
May 12, 2026
Highlights
Even as temperatures rise on Earth’s surface and in the lower atmosphere, the planet’s upper atmosphere has cooled dramatically. This paradoxical pattern is a well-known sign of humanity’s climate impacts—but until now, the underlying physics has remained a mystery.
In a new study, researchers from Columbia University describe the phenomenon’s mechanics, illuminating how it is largely determined by the way carbon dioxide (CO₂) interacts with different wavelengths of light.
“It explains a phenomenon that’s a fingerprint of climate change, has been known to occur for decades, and has not been understood,” says Robert Pincus, a research professor of ocean and climate physics at Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School, and co-author of the study published in Nature Geoscience.
In the lower atmosphere, CO₂ molecules trap heat that would otherwise escape into space. Higher in the atmosphere, though, the dynamics change. In the stratosphere—the atmospheric layer that extends from about 11km to 50 km above Earth’s surface—CO₂ molecules function almost like a radiator, absorbing infrared energy from below and emitting some of that energy into space. When more CO₂ is added, the stratosphere radiates heat away more efficiently and it cools.
…
Cohen, S., Pincus, R. & Polvani, L.M. Stratospheric cooling and amplification of radiative forcing with rising carbon dioxide. Nat. Geosci. 19, 507–512 (2026). https://doi.org/10.1038/s41561-026-01965-8May 12, 2026
Highlights
- Researchers explain why rising carbon dioxide cools the stratosphere even as it warms Earth’s surface and lower atmosphere.
- The study shows this cooling is largely controlled by how CO₂ interacts with different wavelengths of infrared light.
- As CO₂ levels rise, the range of infrared wavelengths involved in stratospheric cooling expands.
- The findings help explain how stratospheric cooling strengthens CO₂’s heat-trapping effect.
Even as temperatures rise on Earth’s surface and in the lower atmosphere, the planet’s upper atmosphere has cooled dramatically. This paradoxical pattern is a well-known sign of humanity’s climate impacts—but until now, the underlying physics has remained a mystery.
In a new study, researchers from Columbia University describe the phenomenon’s mechanics, illuminating how it is largely determined by the way carbon dioxide (CO₂) interacts with different wavelengths of light.
“It explains a phenomenon that’s a fingerprint of climate change, has been known to occur for decades, and has not been understood,” says Robert Pincus, a research professor of ocean and climate physics at Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School, and co-author of the study published in Nature Geoscience.
In the lower atmosphere, CO₂ molecules trap heat that would otherwise escape into space. Higher in the atmosphere, though, the dynamics change. In the stratosphere—the atmospheric layer that extends from about 11km to 50 km above Earth’s surface—CO₂ molecules function almost like a radiator, absorbing infrared energy from below and emitting some of that energy into space. When more CO₂ is added, the stratosphere radiates heat away more efficiently and it cools.
…