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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-229
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-229
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  09 Jul 2020

09 Jul 2020

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This preprint is currently under review for the journal BG.

Global climate response to idealized deforestation in CMIP6 models

Lena Boysen1, Victor Brovkin1,2, Julia Pongratz1,3, David Lawrence4, Peter Lawrence4, Nicolas Vuichard5, Philippe Peylin5, Spencer Liddicoat6, Tomohiro Hajima7, Yanwu Zhang8, Matthias Rocher9, Christine Delire9, Roland Séférian9, Vivek K. Arora10, Lars Nieradzik11, Peter Anthoni12, Wim Thiery13, Marysa Laguë14, Deborah Lawrence15, and Min-Hui Lo16 Lena Boysen et al.
  • 1The land in the Earth System, Hamburg, Germany
  • 2Center for Earth System Research and Sustainability, Universität Hamburg, Germany
  • 3LMU, Department of Geography, Munich, Germany
  • 4Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 5Laboratoire des Sciences du Climat et de l'Environnement, Gif-Sur-Yvette, France
  • 6Met Office Hadley Centre, Exeter, UK
  • 7Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
  • 8Beijing Climate Center, China Meteorological Administration, Beijing, China
  • 9CNRS, Université de Toulouse, Météo-France, Toulouse, France
  • 10Canadian Centre for Climate Modelling and Analysis, Environment and Climate Change Canada, Victoria, BC, Canada
  • 11Institute for Physical Geography and Ecosystem Sciences, Lund University, Lund, Sweden
  • 12Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research/Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany
  • 13Vrije Universiteit Brussel, Department of Hydrology and Hydraulic Engineering, Brussels, Belgium
  • 14University of California, Berkeley, Department of Earth and Planetary Science, Berkeley, CA, USA
  • 15Environmental Sciences, University of Virginia, Charlottesville, VA, USA
  • 16Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan

Abstract. Changes in forest cover have a strong effect on climate through the alteration of surface biogeophysical and biogeochemical properties that affect energy, water, and carbon exchange with the atmosphere. To quantify biogeophysical and biogeochemical effects of deforestation in a consistent setup, nine Earth System models carried out an idealized experiment in the framework of the Coupled Model Intercomparison Project, phase 6 (CMIP6). Starting from their pre-industrial state, models linearly replace 20 million km2 of tree area in densely forested regions with grasslands over a period of 50 years followed by a stabilization period of 30 years. Most of the deforested area is in tropics, with a secondary peak in the boreal region. This study compares the effect of this large deforestation perturbation on energy and carbon fluxes across models. The effect on global annual near-surface temperature ranges from no significant change to a cooling by 0.55 °C, with a multi-model mean of −0.22 ± 0.21 °C. Five models simulate a temperature increase over deforested land in the tropics and a cooling over deforested boreal land. In these models, the latitude at which the temperature response changes sign ranges from 11 to 43° N, with a multi-model mean of 23° N. A multi-ensemble analysis reveals that the near-surface temperature changes emerge within 50 years over the tropical regions propagating from the centre of deforestation to the edges, indicating the influence of non-local effects. The biogeochemical effect of deforestation are land carbon losses of 259 ± 80 PgC. Based on transient climate response to cumulative emissions (TCRE) this would yield a warming by 0.46 ± 0.22 °C, suggesting a net warming effect of deforestation. While there is general agreement across models in their response to deforestation in terms of change in global temperatures and land carbon pools, the underlying changes in energy and carbon fluxes diverge substantially across models and geographical regions. Future analyses of the global deforestation experiments could further explore the effect on changes in seasonality of the climate response as well as large-scale circulation changes to advance our understanding and quantification of deforestation effects in the ESM frameworks.

Lena Boysen et al.

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Short summary
We find a biogeophysically-induced global cooling with strong carbon losses after 20 million km2 idealized deforestation experiment performed with nine CMIP6 Earth System Models. It takes many decades for temperature signal to emerge, with non-local effects playing an important role. Despite a consistent experimental setup, models diverge substantially in climate response, especially in tropics. This study offers unprecedented insights for understanding land-use change effects in CMIP6 models.
We find a biogeophysically-induced global cooling with strong carbon losses after 20 million km2...
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