Recent Temperature and Energy Imbalance Trends Point to Higher Estimates of Future Warming

Abstract

Climate models simulate a wide range of 21st century warming for a given forcing scenario. Constraining this uncertainty is a central challenge in climate science because of its implications for climate policy and adaptation. The transient climate response (TCR) is a key idealized metric used to quantify future warming in response to an exponentially increasing CO ₂ concentration. Climate models span a range of 1.3–3 K for TCR. In attempts to constrain this range, emergent constraints on TCR based on historical temperature trends consistently pointed toward TCR values at the lower end of the range of models. However, recent evidence from trends in the short‐wave and long‐wave components of Earth's energy imbalance (EEI) at the top‐of‐atmosphere suggests that models with higher TCR lie closer to the observed EEI trends. Here, we reconcile this discrepancy and provide a revised range for TCR of 1.9–2.6 K. Using a statistical variability‐filtering approach, we show that previous temperature‐based constraints were biased low due to internal variability, according to our method. We then provide an EEI‐based constraint and demonstrate that short‐ and long‐wave EEI trends have a strong potential to constrain future warming, due to the much larger inter‐model spread in EEI compared to surface temperature. When considering the recent 2001–2025 period, our results show that both surface temperature and EEI trends support higher TCR values than previously estimated. This result implies that it is increasingly difficult to exclude high climate sensitivity models from the plausible range of future warming.