Researchers have supposedly solved a long-standing atmospheric puzzle: How rising carbon dioxide cools the stratosphere even as it warms Earth’s surface and lower atmosphere.
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.
This was predicted in the 1960s by climatologist Syukuro Manabe’s Nobel Prize-winning models of Earth’s climate and CO2-induced global warming. The stratosphere has cooled by roughly 2 degrees Celsius since the mid-1980s. That’s estimated to be more than 10 times the amount of cooling that would have occurred in the absence of human-caused CO2 emissions.
However, though the basic principles of stratospheric cooling are understood, the specifics have remained cloudy. “The existing theory was incredibly insightful, but at the moment we lack a quantitative theory for CO2-induced stratospheric cooling,” says Sean Cohen, a postdoctoral research scientist at Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School, and the study’s lead author.
Cohen, Pincus, and Lorenzo Polvani, a geophysicist in Columbia Engineering’s Department of Applied Physics and Applied Mathematics, developed their theory through an iterative method of identifying the key processes involved in stratospheric cooling, assigning mathematical values to them, comparing the results of their pen-and-paper models to comprehensive simulations and real-world data, tweaking their equations and repeating. Over several months they deduced the equations that best fit.
The researchers arrived at a central factor: how CO2 molecules interact with light, and in particular infrared—also known as longwave—light. Not every infrared wavelength passes through them in the same way. Some wavelengths contribute to cooling more than others, and the team determined that wavelengths in a certain “Goldilocks zone” are especially efficient. As CO2 accumulates in the atmosphere, that zone expands.
“It’s those changes in efficiency that are going to ultimately be what’s driving stratospheric cooling,” says Cohen.
The researchers also quantified the roles played by ozone and water vapor. These are implicated in similar processes as CO2—they too can trap heat in the lower atmosphere but contribute to cooling in the stratosphere by radiating heat—but turn out to have little influence compared with CO2.
The researchers’ equations fit with three well-described phenomena: How stratospheric cooling varies by altitude, with the least cooling occurring at its lowest level and the most at its highest level; how each doubling of CO2 translates to a cooling of 8 degrees Celsius at the stratopause, or the stratosphere’s upper reaches; and how a cooler stratosphere lets less infrared energy escape to space, increasing CO2’s heat-trapping effect. In other words: CO2 makes the stratosphere better at radiating, which cools it—but because it becomes colder, the Earth system ends up losing less heat to space overall, strengthening warming below.
“Here’s this process that we’ve known about for 50-plus years, and we had a pretty decent qualitative understanding of how it worked. However, we didn’t understand the details of what actually drove that process mechanistically,” says Cohen.
Cohen and Pincus say the implications of the work are less about adding one more piece of evidence to support global warming—that reality is already clear—than developing a better understanding of the mechanisms involved in stratospheric cooling. “This is really telling us what is essential,” says Pincus, and it can inform future research on the process. The findings may also help scientists studying conditions outside of Earth.
“Maybe we can better understand what’s going on in the stratospheres of other planets in our solar system or exoplanets,” says Cohen.
Political correct word salad, meaningless and only 100% wrong!!
A cold atmosphere can not heat its own heat source (the surface warm the atmosphere via convection after being heated by the sun), i.e “Back Radiation” – the foundation of the AGW-theory is therefor impossible.
An outdated trope.
Does your duvet heat you whilst in bed?
It to is not a heat source as it is colder than your body.
EM can be and is being attenuated to the same effect as an insulating body to convection.
In the case of the GHE, by the attenuation of LWIR exiting Earth to space, via the absorption and re-emittance (including molecular collisions) of same in all directions – the net flow coming from below.
The attenuation being because the re-emittance becomes progressively weaker with height.
Why was there not a researcher in the room screaming about causality paradigms.
$$$
Whatever CO2 can do, H2O can do better! I don’t think that CO2 behaves differently depending on its distance from the center of the planet. Certain aspects of it may be more detectable in different environments, i.e. there are fewer competing phenomena to mask over the characteristic. Kirchhoff’s Law says that ε = α for any given λ. CO2 like any substance radiates from hot to cold. At higher altitudes it would radiate to space, cooling what is nearby. At lower altitudes it would still radiate to colder bodies, and gain heat from warmer bodies. In the end, the heat will find its way to the coldest place, deep space. They are Columbia University, so they must be right, right? I think their original premise is guiding their conclusion. Start with the idea that CO2 is a minor player in Earth’s temperature. After all, when there was 10x as much CO2 in the atmosphere, the temperature wasn’t that much different and life thrived in that CO2 rich environment.
One of the difficulties comes from the 1800s.
They used the expressions “sensible heat” and “heat radiation.”
Eunice Foote in 1850 or so discovered that thermal energy and EM energy are different.
That discovery is rarely mention, but it was her top discovery.
CO2 as a solid (aka dry ice) does radiate as you state.
CO2 as a gas does not radiate hot to cold.
Thermal energy flows from hot to cold via kinetics, not IR.
Heat (i.e., thermal) radiation does not follow 1/r^2. It follows 1/r^3. Why? It has to fill the volume of the sphere, given a single point source, it has to pass kinetic energy to all of the atoms, molecules, and miscellaneous particles within the spherical volume.
Heat does not go into space as there is nothing for kinetic interactions.
IR doe radiate into space and again, IR is not thermal energy and is not heat.
A lot of this was invented physics trying to prove CO2 is the single control knob.
Talking about “invented physics”:
— CO2 as a gas does not radiate hot to cold
— Thermal energy flows from hot to cold via kinetics, not IR
— radiation does not follow 1/r^2. It follows 1/r^3
— heat does not go into space as there is nothing for kinetic interactions