The Effects of CO2 Forcing on Climate Sensitivity

Scientists discovered that when more carbon dioxide is released into the atmosphere, it becomes a more potent greenhouse gas.

The new study, headed by scientists at the University of Miami Rosenstiel School of Marine, was published in Science this week as world leaders gather in Dubai, United Arab Emirates, for the United Nations Climate Change Conference COP28.

Our finding means that as the climate responds to increases in carbon dioxide, carbon dioxide itself becomes a more potent greenhouse gas. It is yet further confirmation that carbon emissions must be curbed sooner rather than later to avoid the most severe impacts of climate change.

Brian Soden, Study Senior Author and Professor, Atmospheric Sciences, Rosenstiel School of Marine, Atmospheric Science, University of Miami

In this study, the impact of rising CO₂ on the stratosphere, an area of the upper atmosphere that is known to cool with rising CO₂ concentrations, was examined using cutting-edge climate models and additional instruments. It was discovered that the cooling of the stratosphere results in a greater heat-trapping effect from subsequent increases in CO₂, making it a stronger greenhouse gas.

For a long time, scientists believed that radiative forcing—the amount of heat trapped in the atmosphere as a result of a proportionate rise in CO₂—was a constant that did not vary over time.

This new finding shows that the radiative forcing is not constant but changes as the climate responds to increases in carbon dioxide.

Ryan Kramer, Physical Scientist, Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration

By retaining heat energy inside the climate system, carbon dioxide causes global warming.

Future increases in CO₂ will provide a more potent warming effect on climate than an equivalent increase in the past. 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.

Haozhe He, Study Lead Author and PhD Student, University of Miami

The Coupled Model Intercomparison Projects (CMIP), which offer a series of coordinated experiments carried out by dozens of the most comprehensive climate models in the world in support of the IPCC assessments, supplied a suite of climate model simulations for the work. The research team also conducted several “offline” radiative flux estimates using extremely accurate radiative transfer models and analytical models to make their findings conclusive outside of the simulated world of climate models.

The study was released in the Science journal on December 1^st, 2023. The study’s coauthor is Nadir Jeevanjee of NOAA’s Geophysical Fluid Dynamics Laboratory.

NOAA grants NA18OAR4310269 and NA21OAR4310351) and the National Aeronautics and Space Administration (Science of Terra, Aqua, and Suomi-NPP NASA grant 80NSSC21K1968) sponsored the study.

Journal Reference:

He, H, et. al. (2023) State dependence of CO₂ forcing and its implications for climate sensitivity. Science. doi:10.1126/science.abq6872