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Anthropogenic carbon release rate unprecedented during the past 66 million years

Abstract

Carbon release rates from anthropogenic sources reached a record high of 10 Pg C yr−1 in 2014. Geologic analogues from past transient climate changes could provide invaluable constraints on the response of the climate system to such perturbations, but only if the associated carbon release rates can be reliably reconstructed. The Palaeocene–Eocene Thermal Maximum (PETM) is known at present to have the highest carbon release rates of the past 66 million years, but robust estimates of the initial rate and onset duration are hindered by uncertainties in age models. Here we introduce a new method to extract rates of change from a sedimentary record based on the relative timing of climate and carbon cycle changes, without the need for an age model. We apply this method to stable carbon and oxygen isotope records from the New Jersey shelf using time-series analysis and carbon cycle–climate modelling. We calculate that the initial carbon release during the onset of the PETM occurred over at least 4,000 years. This constrains the maximum sustained PETM carbon release rate to less than 1.1 Pg C yr−1. We conclude that, given currently available records, the present anthropogenic carbon release rate is unprecedented during the past 66 million years. We suggest that such a ‘no-analogue’ state represents a fundamental challenge in constraining future climate projections. Also, future ecosystem disruptions are likely to exceed the relatively limited extinctions observed at the PETM.

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Figure 1: Selected stable isotope records from New Jersey margin sections across the PETM onset16,20,21,23.
Figure 2: Millville PETM records and time-series analysis.
Figure 3: Examples of model time lags (τmod) as a function of model release time (tin).
Figure 4: Determining the minimum release time.

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Acknowledgements

We thank E. Thomas for sharing data and G. Bowen for discussions. We gratefully acknowledge the NO.COM.ET project. This research was supported by NSF grant OCE12-20602 to J.C.Z. and R.E.Z. and EU grant ERC-2013-CoG-617313 to A.R.

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R.E.Z. led the effort. All authors wrote the paper.

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Correspondence to Richard E. Zeebe.

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Zeebe, R., Ridgwell, A. & Zachos, J. Anthropogenic carbon release rate unprecedented during the past 66 million years. Nature Geosci 9, 325–329 (2016). https://doi.org/10.1038/ngeo2681

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