AOSC Seminar by Clark Jay Weaver, 09/17/2026
AOSC Seminar
Clark Jay Weaver
UMD/ESSIC
Title
Accelerating Warming and the Shortwave Cloud Feedback: Evaluating CMIP6 using a 45-Year UV Cloud Record
Abstract
We review shortwave (SW) climate feedbacks and compare the recent acceleration in global mean temperatures with absorbed shortwave radiation trends from CERES. A primary driver of uncertainty in Equilibrium Climate Sensitivity (ECS) among CMIP6 models is the representation of these SW cloud feedbacks. To help narrow this uncertainty, we present a novel 45-year (1980-2025) record of top-of-atmosphere (TOA) shortwave cloud albedo, derived from 340 nm UV radiances across multiple NASA and NOAA satellite instruments.
Our analysis reveals a pronounced decrease in the albedo of marine low- and mid-level clouds beginning around 2010. We attribute this decline to shifts in the sea surface temperature (SST) "pattern effect," which coincides with the accelerated global warming observed in the NOAA v6 SST record. This observed cloud albedo trend is robust and closely mirrors independent observations from the CERES EBAF dataset.
When evaluating the shortwave cloud feedback parameter against historical and SSP2-4.5 CMIP6 simulations, our full 45-year record yields a neutral feedback. However, when isolated to the post-2000 period, the observational feedback estimate becomes strongly positive (approximately 1.0 to 1.5 W/m2/K), exceeding nearly all published CMIP6 projections. The fact that two independent satellite records reveal a recent, sharp reduction in cloud albedo--a feature largely absent in current climate models--suggests that near-term warming trajectories may be significantly underestimated. Finally, we will briefly discuss our ongoing efforts to communicate critical climate science findings to members and staffers of the U.S. Congress.
Bio
Clark Weaver is a Research Scientist who has worked for over 30 years with the Atmospheric Chemistry and Dynamics Branch at NASA’s Goddard Space Flight Center. His current research focuses on understanding shortwave radiative feedbacks from clouds, boundary layer thermodynamics, and land-atmosphere interactions.
Throughout his career at NASA, He has developed retrieval algorithms for aerosols, ozone, methane, and carbon dioxide from various passive and active satellite and airborne instruments. His early work assessed the impact of supersonic aircraft on the ozone layer by comparing chemistry and transport model simulations with satellite observations. Later, his research into the radiative forcing of dust successfully uncovered a bias in TOVS temperature retrievals during heavy aerosol loading conditions.
He earned his undergraduate degree from The Ohio State University in 1982. That same year, he served as a member of a Byrd Polar Research expedition to the Quelccaya Ice Cap in Peru, drilling and extracting ice cores that allowed scientists to study 1,500 years of tropical climate change. He subsequently earned his Ph.D. from Colorado State University in 1987, where his dissertation focused on the entrainment of marine stratocumulus clouds.
Beyond his scientific research, Dr. Weaver has been deeply engaged in climate science advocacy on Capitol Hill for the past 15 years. He has conducted numerous briefings with Congressional staff on science and policy, and participated in Brookings Institution meetings regarding carbon pricing at the local, national, and global levels. He also develops and maintains TemperatureTrends.org, a data visualization dashboard designed to help Members of Congress and their staff clearly see the impacts of changing temperature extremes on their constituents.
Contact
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AOSC Seminar
Pre-seminar refreshment: N/A
Seminar: 3:30-4:30pm, Room: ATL 2400(only when in-person)
Meet-the-Speaker: 4:30-5:00pm, Room: ATL 3400(only when in-person) [For AOSC Students only]
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