| 21 Jan 2026
Climate models with moderate climate sensitivity best simulate the magnitude of Earth's energy imbalance
Abstract. Recent studies have highlighted that state-of-the-art climate models are not able to simulate the large observed trend in Earth's energy imbalance. Here we evaluate climate models' ability to represent both the trend and the magnitude of the imbalance, while accounting for model energy leakage and remnant drift. As reference we use satellite observations and we find that every observed annual mean energy imbalance is within the range simulated by models, including the record year 2023, and when averaged over the 2001–2024 period, 15 out of 30 models simulate magnitudes of the imbalance that are statistically consistent with the observations. Models, however, generally underestimate the positive trend in the energy imbalance, albeit barely within the range of uncertainty. We suspected that a discontinuity in volcanic forcing between the historical and future scenario in 2014–2015 could have caused the underestimated trend, but only found evidence of such artifacts for a few models. Finally, we find a weak correlation between short-term decadal warming and energy imbalance, but a surprisingly close relationship between energy imbalance and equilibrium climate sensitivity. Based on observational constraints, the relationship suggests that models with moderate climate sensitivity are most realistic.
General comments
This study examines the recent positive trend and magnitude of the observed Earth’s Energy Imbalance (EEI) and evaluates their reproducibility in CMIP6 models. The authors demonstrate that while the magnitude of EEI is well captured by CMIP6 models, its positive trend is underestimated by most of them. They further identify a close relationship between EEI and equilibrium climate sensitivity (ECS) and attempt to constrain ECS using the observed EEI magnitude, suggesting that models with moderate ECS values are more consistent with observations.
Overall, the manuscript is well written, and the results are interesting and supported by robust analyses. I recommend publication after minor revisions.
Specific comments
I understood that a positive sign indicates energy input into the system, whereas a negative sign indicates energy loss. If this understanding is incorrect, please clarify. Based on Figure 2, the global mean temperature appears to increase when the energy imbalance is positive, which seems consistent with net energy input.
I found this discussion somewhat confusing. You state that the cooler global temperature associated with internal variability during the first period leads to a larger energy imbalance through the negative feedback term (λΔTs). However, my understanding is that this term represents the response to anthropogenic forcing, while the effect of internal variability is captured by ε. Please clarify this point and elaborate on the underlying argument in more detail.
I understand that models with larger ECS tend to have smaller (weaker) negative climate feedback parameters λ. However, the magnitude of λΔT also depends on the value of ΔT. My understanding is that larger-ECS models compensate for energy imbalance through a larger increase in ΔT compared to smaller-ECS models, suggesting that the behavior of λΔT may not be straightforward. Please clarify this interpretation.
Technical corrections
Shared Socioeconomic Pathway SSP2-4.5 → Shared Socioeconomic Pathway (SSP) 2-4.5
The gray lines are too thin to be easily distinguishable. It would be helpful to slightly thicken the lines or use different colors. In addition, please include information about these lines in the figure legend.
“Multi-model ensemble mean/range” would be more appropriate than “Model mean/range.”
The legends are too small. I suggest placing the legends outside the figures, increasing the font size, and arranging them in two columns.