Published On 5/20/2026
The cooling of the stratosphere resulting from rising carbon dioxide concentrations is not just a side effect of global warming, but rather represents an essential part of the mechanism that increases the strength of this gas’s influence on the Earth’s climate, according to a new study indicating that this cooling increases what is known as “radiative forcing” of carbon dioxide by about 50%, meaning that it increases the amount of energy that the Earth’s climate system reserves.
The study, published on May 11 in the journal Nature Geoscience, provides a new explanation for a phenomenon that scientists have known for decades. When carbon dioxide concentrations rise, the lower layers of the atmosphere near the Earth’s surface heat up, while the stratosphere, which is the layer above it and extends approximately between an altitude of 10 and 50 kilometers, cools. This cooling has long been considered one of the clearest signatures of human influence on climate, but its physical details were not fully understood.
Why does the stratosphere cool as carbon dioxide increases?
The conventional explanation is that carbon dioxide acts as a greenhouse gas, meaning it traps part of the heat emanating from the Earth’s surface, says study lead author Sean Kuhn, a postdoctoral researcher at the Lamont-Doherty Earth Observatory at Columbia University. But the new study shows that it is not only related to the increased thickness of the atmosphere in the face of thermal radiation, but it is also related to the precise spectral properties of carbon dioxide, that is, the way this gas absorbs and releases heat at certain wavelengths of infrared radiation.
Using advanced models that simulate the transfer of thermal radiation within the atmosphere, along with precise spectral calculations, the researchers found that increased carbon dioxide makes the stratosphere more capable of losing heat to outer space. This occurs in specific ranges of infrared radiation, where the gas becomes able to release heat very efficiently.
Kuhn simplifies the idea and says in statements to Al Jazeera Net: “It can be imagined that there is a certain part of the thermal spectrum that acts as a “suitable window” for heat to escape from the stratosphere into space. This window is not so closed that it prevents heat from escaping, nor is it completely open so that the gas does not interact with it, but rather it is located in a middle region that allows carbon dioxide to release heat efficiently.” The researcher describes this area metaphorically as the “Goldilocks View”, that is, the range that is just right for heat loss.
As the concentration of carbon dioxide increases, this effective spectral region expands, causing the stratosphere to lose more heat and then cool. The study shows that this cooling does not occur with the same force in all parts of the stratosphere, but rather increases as we rise to the top of this layer. Every doubling in the concentration of carbon dioxide may lead to a cooling of up to about 8 degrees Kelvin near the “stratopoise,” which is the upper region of the stratosphere at an altitude of approximately 50 kilometers, while cooling is very limited near the “tropopause,” that is, the border between the stratosphere and the lower layer of the atmosphere.
How does this cooling increase the power of warming?
The lead author believes that the study’s greatest importance lies not only in explaining why the stratosphere cools, but also in showing that this cooling itself increases the strength of carbon dioxide’s influence on the climate. Radiative forcing, simply put, is the amount of imbalance that occurs in the Earth’s energy balance when greenhouse gases increase. The greater this coercion, the more energy is trapped within the climate system, and the greater the potential for warming.
When carbon dioxide levels rise, the atmosphere prevents a larger portion of the heat rising from the Earth’s surface from escaping directly into space. But when the stratosphere cools, this layer becomes less able to radiate heat back out. Thus, not only does carbon dioxide block more heat, but the upper layer that could have released part of this heat becomes colder, releasing less energy. The result is that more energy is trapped within the climate system.
The study’s calculations indicate that this “stratospheric modification” increases the radiative forcing of carbon dioxide by about 40 to 60% compared to the instantaneous value resulting from increasing the gas concentration alone. The instantaneous radiative forcing of carbon dioxide is about 2.2 watts per square meter, but it rises to about 3.4 watts per square meter after stratospheric cooling is taken into account.
The researchers also found that this effect remains almost constant even with differences in Earth’s surface temperatures, which means that stratospheric cooling is not a secondary or temporary detail, but rather an essential and relatively stable element in the climate’s response to rising carbon dioxide. The study also indicates that what happens with carbon dioxide is not necessarily a general rule that applies to all greenhouse gases.
Despite the importance of the results, the researchers explain that the study relied on relatively simplified models to isolate the radiative effect of carbon dioxide. The study also used single-column models, which are useful for understanding basic physics, but they do not represent all the complexities of the real atmosphere, such as global wind movement, clouds, seasonal changes, and interactions between different layers. The study also did not address in detail some of the chemical and dynamic processes that may affect the stratosphere, such as the effect of temperature change on the chemistry of ozone, or the change in air circulation in this layer.
In terms of funding, the research received support from the US National Science Foundation through several research grants in atmospheric sciences. The researchers also pointed to scientific contributions from colleagues who provided observations and reviews during the preparation of the study.
