Why is the response of the global average surface temperature to a doubling of carbon dioxide greater than what previous generations of models have predicted?
That is the central question in an Eos Research Spotlight by David Shultz.
The author writes, “Earth system models represent our best attempts at simulating the global climate. They are far from perfect, but they’re improving all the time, and they allow researchers to ask interesting what-if questions about Earth’s future. Pressing among these questions is, ‘How much hotter would it get if we instantaneously doubled atmospheric carbon dioxide?’”
For answers, Shultz turns to RGMA scientist Mark Zelinka of Lawrence Livermore National Laboratory and his collaborators who authored “Causes of Higher Climate Sensitivity in CMIP6 Models,” in a recent edition of Geophysical Research Letters.
The research finds that increased sensitivity can be linked to changes in how clouds respond to warming in the southern middle latitudes. “Specifically,” Shultz writes, “in the latest models, both cloud areal coverage and water content decrease at these latitudes. With fewer bright white clouds reflecting sunlight back into space, the planet absorbs more energy and gets hotter, and even fewer clouds form. This amplifying feedback, the researchers argue, is responsible for the bulk of the increased climate sensitivity seen in the current models.”