Stratosphere cooling caused by CO2 causes subsequent increases in CO2 to have a larger heat-trapping effect.
The effect of increasing the concentration of atmospheric carbon dioxide (CO2) on global average surface air temperature might be expected to be constant, but this is not the case. A study published in the journal Science shows that carbon dioxide becomes a more potent greenhouse gas as more is released into the atmosphere.
The researchers used climate models and other tools to analyze the effect increasing CO2 has on a region of the upper atmosphere — the stratosphere — that scientists have long known cools with increasing CO2 concentrations. They found that this stratosphere cooling causes subsequent increases in CO2 to have a larger heat-trapping effect than previous increases, causing carbon dioxide to become more potent as a greenhouse gas.
The amount of heat trapped in the atmosphere from a proportionate increase in CO2, which scientists refer to as radiative forcing, has long been thought of as a constant that does not change over time. In fact, doubling the atmospheric CO2 concentration increases the impact of any given increase in CO2 by about 25%
“Future increases in CO2 will provide a more potent warming effect on climate than an equivalent increase in the past,” said the study’s lead author Haozhe He, who completed the work as part of his Ph.D. studies at the University of Miami. “This new understanding has significant implications for interpreting both past and future climate changes and implies that high CO2 climates may be intrinsically more sensitive than low CO2 climates.”
See: State dependence of CO2 forcing and its implications for climate sensitivity, Science, Nov. 30 2023