Preprints
https://doi.org/10.5194/bg-2020-432
https://doi.org/10.5194/bg-2020-432

  30 Nov 2020

30 Nov 2020

Review status: a revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

Earth system feedbacks following large-scale tropical forest restoration

Alexander Koch1,a, Chris Brierley1, and Simon L. Lewis1,2 Alexander Koch et al.
  • 1Department of Geography, University College London, Gower Street, WC1E 6BT London, UK
  • 2School of Geography, University of Leeds, LS2 9JT Leeds, UK
  • anow at: Department of Earth Sciences, University of Hong Kong, Hong Kong, HKSAR

Abstract. To achieve the Paris Agreement requires aggressive mitigation strategies alongside negative emission technologies. Recent studies suggest that increasing tree cover can make a substantial contribution to negative emissions, with the tropics being the most suitable region from a biogeophysical perspective. Yet these studies typically do not account for subsequent carbon cycle and climate feedback processes of large-scale land use change. Here we quantify the maximum potential temperature and CO2 benefits from pantropical forest restoration, including earth system feedbacks, using a fully-coupled, emission-driven Earth System Model (HadGEM2-ES). We perform an idealised experiment where all land use in the tropics is stopped and vegetation is allowed to recover, on top of an aggressive mitigation scenario (RCP 2.6). We find that tropical restoration of 1529 Mha increases carbon stored in live biomass by 130 Pg C by 2100 CE. Whilst avoiding deforestation and tropical restoration in the tropics removes 42 Pg C compared to RCP 2.6, feedback processes mean that carbon in the atmosphere only reduces by 18 Pg C by 2100. The resulting, small CO2 (9 ppm) benefit does not translate to a detectable reduction in global surface air temperature compared to the control experiment. The greatest carbon benefit is achieved 30–50 years after restoration before the Earth System response adjusts to the new land-use regime and declining fossil fuel use. We identify three model-independent key points: (i) the carbon benefit of restoration is CO2-scenario dependent, (ii) in a world that follows Paris Agreement emission cuts restoration is best deployed immediately, and (iii) the ocean carbon feedbacks will reduce the efficacy of negative emissions technologies. We conclude that forest restoration can reduce peak CO2 mid-century, but can only be a modest contribution to negative emissions.

Alexander Koch et al.

 
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Status: closed
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Alexander Koch et al.

Model code and software

Earth system feedbacks following large-scale tropical forest restoration (code & data) Alexander Koch https://doi.org/10.17632/j39bw4rzsr.1

Alexander Koch et al.

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Short summary
Estimates of large scale tree planting and forest restoration as carbon sequestration tool typically miss one crucial aspect: the earth system response to the increased land carbon sink from the new vegetation. We assess the impact of tropical forest restoration using an Earth System Model under a scenario that limits warming to 2C. Almost two-thirds of the carbon impact of forest restoration is offset by negative carbon cycle feedbacks suggesting a more modest benefit than in previous studies.
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