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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 11 | Copyright
Atmos. Chem. Phys., 17, 7213-7228, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 16 Jun 2017

Research article | 16 Jun 2017

A modified impulse-response representation of the global near-surface air temperature and atmospheric concentration response to carbon dioxide emissions

Richard J. Millar1,2,3, Zebedee R. Nicholls1,4,5, Pierre Friedlingstein3, and Myles R. Allen1,2,6 Richard J. Millar et al.
  • 1Department of Physics, University of Oxford, Oxford, UK
  • 2Oxford Martin Net Zero Carbon Investment Initiative, Oxford Martin School, University of Oxford, Oxford, UK
  • 3Department of Mathematics, University of Exeter, Exeter, UK
  • 4Australian-German Climate & Energy College, University of Melbourne, Parkville, Victoria, Australia
  • 5Department of Earth Sciences, University of Melbourne, Parkville, Victoria, Australia
  • 6Environmental Change Institute, University of Oxford, Oxford, UK

Abstract. Projections of the response to anthropogenic emission scenarios, evaluation of some greenhouse gas metrics, and estimates of the social cost of carbon often require a simple model that links emissions of carbon dioxide (CO2) to atmospheric concentrations and global temperature changes. An essential requirement of such a model is to reproduce typical global surface temperature and atmospheric CO2 responses displayed by more complex Earth system models (ESMs) under a range of emission scenarios, as well as an ability to sample the range of ESM response in a transparent, accessible and reproducible form. Here we adapt the simple model of the Intergovernmental Panel on Climate Change 5th Assessment Report (IPCC AR5) to explicitly represent the state dependence of the CO2 airborne fraction. Our adapted model (FAIR) reproduces the range of behaviour shown in full and intermediate complexity ESMs under several idealised carbon pulse and exponential concentration increase experiments. We find that the inclusion of a linear increase in 100-year integrated airborne fraction with cumulative carbon uptake and global temperature change substantially improves the representation of the response of the climate system to CO2 on a range of timescales and under a range of experimental designs.

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Simple representations of the global coupled climate–carbon-cycle system are required for climate policy analysis. Existing models have often failed to capture important physical dependencies of the climate response to carbon dioxide emissions. In this paper we propose a simple but novel modification to impulse-response climate–carbon-cycle models to capture these physical dependencies. This simple model creates an important tool for both climate policy and climate science analysis.
Simple representations of the global coupled climate–carbon-cycle system are required for...