Caltech-Google study finds low clouds accelerate warming

Researchers at the California Institute of Technology and Google Alphabet Inc. ↗ 1.53% have published findings showing that low-level clouds over the tropical Pacific are thinning in response to rising carbon dioxide concentrations and warming sea surface temperatures, creating a feedback loop that amplifies global warming beyond what many climate models currently project.

A Massive Simulation Effort

The study, published Thursday in Science Advances, drew on 7,083 high-resolution large-eddy simulations of tropical Pacific low clouds to separate the effects of sea surface warming from the direct radiative impact of CO2 on cloud behavior. The researchers found a "strong, nonlinear cloud response when surface warming is combined with high concentrations of CO2," meaning the thinning effect accelerates as emissions climb rather than increasing at a steady rate.science+1

The work was led by Zhaoyi Shen, a postdoctoral scholar in Caltech's Climate Dynamics Group who studies boundary layer clouds and their feedbacks under climate change. The large dataset was developed in collaboration with Google, leveraging high-performance computing resources to run simulations at a resolution fine enough to capture turbulence and convection within cloud layers.szy21+2

Implications for Climate Sensitivity

"Our results show potentially large rapid adjustments of low clouds to high CO2 concentrations, which suggests the earth's climate might be more" sensitive than standard projections indicate, the Caltech news release stated. The findings add to a growing body of evidence that cloud feedbacks push equilibrium climate sensitivity — the warming expected from a doubling of atmospheric CO2 — toward the higher end of estimated ranges.gps.caltech

Previous work by Caltech's Tapio Schneider, who leads the Climate Dynamics Group, demonstrated in 2019 that CO2 concentrations above 1,200 parts per million could destabilize marine stratocumulus clouds entirely, triggering abrupt warming of about 8 degrees Celsius. The new study suggests that even at lower CO2 levels, the nonlinear response of clouds is already contributing to warming amplification.caltech

A Persistent Scientific Puzzle

Low clouds have long been recognized as the largest source of uncertainty in climate models' estimates of future warming. A separate study published in Science in late 2024 identified record-low planetary albedo — driven largely by reduced low-cloud cover in the northern mid-latitudes and tropics — as a primary factor behind the temperature surge of 2023. The Caltech-Google research offers a mechanistic explanation for why these clouds are disappearing faster than many models predict, pointing to the direct effect of CO2 on cloud dynamics as a previously underappreciated driver.science