Climate Sensitivity from 21st-Century Trends in Earth's Energy Imbalance

Vincent T Cooper 

Earth's energy imbalance has increased rapidly since continuous satellite observations began in 2001, raising concern that equilibrium climate sensitivity may be higher than in recent assessments. Here we use energy-budget trends over 2006–2024 to estimate climate sensitivity in a Bayesian framework, accounting for uncertainty in observations, forcing, variability, and pattern effects. Climate sensitivity inference depends strongly on the likelihood method, and we propose a simple, revised method that is physically consistent with the global energy-balance model. Its maximum likelihood is at 5.2K, whereas the existing method maximizes at 3.0K. Using the revised likelihood and a standard uniform-feedback prior, the posterior median is 3.6K; posterior medians range from 3.3–4.8K depending on the prior. Posterior 66% ranges largely overlap existing assessments of 2–5K and strongly disfavor climate sensitivity below 2K, but upper bounds are prior-dependent. Thus 21st-century trends do not require unusually high climate sensitivity compared to other lines of evidence.