Climate–carbon cycle uncertainties and the Paris Agreement

Abstract

The Paris Agreement1 aims to address the gap between existing climate policies and policies consistent with “holding the increase in global average temperature to well below 2 C”. The feasibility of meeting the target has been questioned both in terms of the possible requirement for negative emissions2 and ongoing debate on the sensitivity of the climate–carbon-cycle system3. Using a sequence of ensembles of a fully dynamic three-dimensional climate–carbon-cycle model, forced by emissions from an integrated assessment model of regional-level climate policy, economy, and technological transformation, we show that a reasonable interpretation of the Paris Agreement is still technically achievable. Specifically, limiting peak (decadal) warming to less than 1.7 °C, or end-of-century warming to less than 1.54 °C, occurs in 50% of our simulations in a policy scenario without net negative emissions or excessive stringency in any policy domain. We evaluate two mitigation scenarios, with 200 gigatonnes of carbon and 307 gigatonnes of carbon post-2017 emissions respectively, quantifying the spatio-temporal variability of warming, precipitation, ocean acidification and marine productivity. Under rapid decarbonization decadal variability dominates the mean response in critical regions, with significant implications for decision-making, demanding impact methodologies that address non-linear spatio-temporal responses. Ignoring carbon-cycle feedback uncertainties (which can explain 47% of peak warming uncertainty) becomes unreasonable under strong mitigation conditions.

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Fig. 1: Summary time series of the 69-member CP, 2P0C and 1P5C E3ME-FTT-GENIE emissions-forced PLASIM-GENIE ensembles.
Fig. 2: DJF surface air temperature scaling patterns and uncertainty.
Fig. 3: JJA precipitation scaling patterns and uncertainty.
Fig. 4: Ocean stressor scaling patterns and uncertainty.

Change history

  • 04 July 2018

    In the version of this Article originally published, H. Pollit’s name was incorrectly listed as H. E. Pollit (H.E.P.) throughout the paper, this has been corrected to H. Pollitt (H.P.) in the online versions of this Article.

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Acknowledgements

We acknowledge C-EERNG and Cambridge Econometrics for support, and funding from EPSRC (to J.-F.M., fellowship number EP/ K007254/1); the Newton Fund (to J.-F.M., P.S. and J.E.V., EPSRC grant number EP/N002504/1 and ESRC grant number ES/N013174/1), NERC (to N.R.E., P.H. and H.P., grant number NE/P015093/1), CONICYT (to P.S.), the Philomathia Foundation (to J.E.V.) and Horizon 2020 (to H.P. and J.-F.M., the Sim4Nexus project).

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P.B.H., N.R.E. and R.D.W. designed and coordinated the Earth system modelling. H.P., J.-F.M. and N.R.E. designed and coordinated the energy-economy modelling. P.B.H., N.R.E., R.D.W. and H.P. wrote the article with contributions from all. P.B.H. performed the PLASIM-GENIE simulations. U.C. performed the E3ME-FTT simulations. All authors developed model components and/or provided scientific support: P.B.H. (ESM coupling), K.F. and F.L. (atmosphere), N.R.E. (ocean), A.R. (biogeochemistry), H.P. and J.F.M. (energy-economic), P.S. and J.-F.M. (power sector), A.L. and J.-F.M. (transport sector), F.K. and J.-F.M. (household heating), J.E.V. (geopolitics) and R.D.W. (statistics).

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Correspondence to P. B. Holden.

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Holden, P.B., Edwards, N.R., Ridgwell, A. et al. Climate–carbon cycle uncertainties and the Paris Agreement. Nature Clim Change 8, 609–613 (2018). https://doi.org/10.1038/s41558-018-0197-7

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