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

State-of-the-art climate models simulate a wide range of future warming for the 21^st century, even when run with identical anthropogenic and natural forcings. Constraining this uncertainty in future warming is a key challenge in climate science: it is the foundation for the calculation of carbon budgets and resulting climate policy, and it is indispensable for the design of appropriate climate adaptation measures on global, regional and local levels. 

The Transient Climate Response (TCR) is an idealized metric commonly used to quantify future warming in climate models. Climate models simulate a wide range of 1-3K for TCR (Forster et al. 2021). Existing emergent constraints on TCR based on historical temperature trends had led to a consistent downward revision of this range at the time when CMIP6 simulations were first published, consistently excluding models with very high TCR values. However, recent evidence based on Earth's energy imbalance (EEI) shows the opposite, i.e., that models with higher TCR values reproduce observed EEI trends better (Myhre et al. 2025). In this work, we address and reconcile this apparent discrepancy. We first improve existing temperature-based constraints by statistically removing internal variability in global temperature and EEI from spatial surface temperature anomalies (Gyuleva et al. 2025). We show that earlier temperature-based TCR constraints were biased low due to cooling variability contributions in recent decades. We then show that recent trends in both variability-adjusted temperature and energy imbalance point to higher TCR values, yet constraints based on shorter and more recent trends are much more uncertain. Our results highlight that constraints based on Earth’s energy imbalance are a valuable source of observational evidence to constrain future warming in addition to temperature-based constraints. Our results further suggest that previous constraints on TCR have to be revised upward due to the combined effects of variability and the inclusion of evidence from Earth’s energy imbalance.

 

 

References

Forster, P., T. Storelvmo, K. Armour, W. Collins, J.-L. Dufresne, D. Frame, D. Lunt, T. Mauritsen, M. Palmer, M. Watanabe, M. Wild, and H. Zhang (2021). “The Earth’s Energy Budget, Climate Feedbacks, and Climate Sensitivity”. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Ed. by V. Masson-Delmotte, P. Zhai, A. Pirani, S. L. Connors, C. P´ean, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelek¸ci, R. Yu, and B. Zhou. Cambridge, United Kingdom; New York, NY, USA: Cambridge University Press, pp. 923–1054. url: https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-7/.

Gyuleva, G., R. Knutti, and S. Sippel (2025). “Combination of Internal Variability and Forced Response Reconciles Observed 2023–2024 Warming”. en. In:Geophysical Research Letters 52.14. eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2025Ge2025GL115270. Issn: 1944-8007. url: https://onlinelibrary.wiley.com/doi/abs/10.1029/2025GL115270 (visited on 08/18/2025).

Myhre, G., Ø. Hodnebrog, N. Loeb, and P. M. Forster (June 2025). “Observed trend in Earth energy imbalance may provide a constraint for low climate sensitivity models”. In: Science 388.6752. Publisher: American Association for the Advancement of Science, pp. 1210–1213. url: https://www.science.org/doi/10.1126/science.adt0647 (visited on 07/04/2025).