Anthropogenic and natural warming inferred from changes in Earth’s energy balance

Abstract

The Earth’s energy balance is key to understanding climate and climate variations that are caused by natural and anthropogenic changes in the atmospheric composition. Despite abundant observational evidence for changes in the energy balance over the past decades1,2,3, the formal detection of climate warming and its attribution to human influence has so far relied mostly on the difference between spatio-temporal warming patterns of natural and anthropogenic origin4,5,6. Here we present an alternative attribution method that relies on the principle of conservation of energy, without assumptions about spatial warming patterns. Based on a massive ensemble of simulations with an intermediate-complexity climate model we demonstrate that known changes in the global energy balance and in radiative forcing tightly constrain the magnitude of anthropogenic warming. We find that since the mid-twentieth century, greenhouse gases contributed 0.85 °C of warming (5–95% uncertainty: 0.6–1.1 °C), about half of which was offset by the cooling effects of aerosols, with a total observed change in global temperature of about 0.56 °C. The observed trends are extremely unlikely (<5%) to be caused by internal variability, even if current models were found to strongly underestimate it. Our method is complementary to optimal fingerprinting attribution and produces fully consistent results, thus suggesting an even higher confidence that human-induced causes dominate the observed warming.

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Figure 1: Radiative forcings and observed and simulated warming using observationally constrained model parameters.
Figure 2: Probabilistic estimates of the historical and future cumulative radiative forcing and the Earth’s energy budget.
Figure 3: Contributions of different forcing agents to the total observed temperature change.
Figure 4: Comparison of observed changes in global mean temperature and energy content with model estimates of internal variability.

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Acknowledgements

We thank Urs Beyerle for the technical support of the climate model. Support for the International Detection and Attribution Working Group (IDAG) by the US Department of Energy’s Office of Science, Office of Biological and Environmental Research grant DE-SC0004956 and the National Oceanic and Atmospheric Administration’s Climate Program Office is acknowledged.

Author information

M.H. performed the climate model computations and statistical analysis. Both authors designed the study and wrote the paper.

Correspondence to Reto Knutti.

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The authors declare no competing financial interests.

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Huber, M., Knutti, R. Anthropogenic and natural warming inferred from changes in Earth’s energy balance. Nature Geosci 5, 31–36 (2012). https://doi.org/10.1038/ngeo1327

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