Cloud feedback refers to the response of clouds to surface temperature change. A positive cloud feedback would amplify greenhouse gas-induced warming and have a stronger cooling effect from aerosol‐cloud interactions. Uncertainties in predicting cloud feedbacks are the largest cause of spread in model predictions of future global warming.
In a recent analysis on CMIP6 climate models reported in Geophysical Research Letters, authors Chenggong Wang, Brian Soden, Wenchang Yang, and Gabriel Vecchi from Princeton University and the University of Miami found that the high-sensitivity climate models tend to predict much greater global warming and produce less plausible projections of Earth’s future climate than the past CMIP model generation. This phenomenon in the latest models is mainly caused by more positive cloud feedback in the high sensitivity models, which exaggerates the global cooling effect from aerosol‐cloud interactions and offsets the warming from greenhouse gases increase during the historical period. Both high-sensitivity models and low-sensitivity models with neutral cloud feedback are able to reproduce a good match with observed historical global mean temperature. Since anthropogenic aerosols primarily concentrate in the Northern Hemisphere, strong aerosol‐cloud interaction models generate unrealistic inter-hemispheric warming asymmetry in the late 20th century, in comparison to the low sensitivity models. Consequently, the high sensitivity climate models project a much warmer climate in future emissions scenarios where aerosols are projected to decrease due to emission reduction policies as greenhouse gases continue to increase.
The results of this study bring a timely reflection on interpreting climate simulations. These findings are also noteworthy when it comes to climate-change policy. "A higher climate sensitivity would obviously necessitate much more aggressive carbon mitigation," the co-author Gabriel Vecchi from Princeton University said, “reducing the uncertainty in climate sensitivity helps us make a more reliable and accurate strategy to deal with climate change."
This research story has also been published by ScienceDaily on March 3, 2021.
Read the full paper here.
Funding for this project was provided in part by the NOAA Climate Program Office, MAPP program.
The Modeling, Analysis, Predictions, and Projections (MAPP) Program is a competitive research program in NOAA Research's Climate Program Office. MAPP's mission is to enhance the Nation's and NOAA's capability to understand, predict, and project variability and long-term changes in Earth's system and mitigate human and economic impacts. To achieve its mission, MAPP supports foundational research, a transition of research to applications, and engagement across other parts of NOAA, among partner agencies, and with the external research community. MAPP plays a crucial role in enabling national preparedness for extreme events like drought and longer-term climate changes. For more information, please visit www.cpo.noaa.gov/MAPP.