23 Feb 2021

23 Feb 2021

Review status: a revised version of this preprint was accepted for the journal BG.

Slow-down of the greening trend in natural vegetation with further rise in atmospheric CO2

Alexander J. Winkler1,2,3, Ranga B. Myneni4, Alexis Hannart5, Stephen Sitch6, Vanessa Haverd7,, Danica Lombardozzi8, Vivek K. Arora9, Julia Pongratz10,1, Julia E. M. S. Nabel1, Daniel S. Goll11, Etsushi Kato12, Hanqin Tian13, Almut Arneth14, Pierre Friedlingstein15, Atul K. Jain16, Sönke Zaehle3, and Victor Brovkin1 Alexander J. Winkler et al.
  • 1Max-Planck-Institute for Meteorology, Bundesstrasse 53, 20146 Hamburg, Germany
  • 2International Max-Planck Research School for Earth System Modeling, Bundesstrasse 53, 20146 Hamburg, Germany
  • 3Max Planck Institute for Biogeochemistry, 07745 Jena, Germany
  • 4Department of Earth and Environment, Boston University, Boston MA 02215, USA
  • 5Ouranos, Montreal QC H2L 1K1, Quebec, Canada
  • 6College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4RJ, UK
  • 7CSIRO Oceans and Atmosphere, Canberra, 2601, Australia
  • 8Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, CO 80302, USA
  • 9Canadian Centre for Climate Modelling and Analysis, Environment and Climate Change Canada, University of Victoria, Victoria, British Columbia, Canada V8W2Y2
  • 10Department of Geography, Ludwig Maximilians University Munich, Luisenstr. 37, Munich D-80333, Germany
  • 11Lehrstuhl fur Physische Geographie mit Schwerpunkt Klimaforschung, Universität Augsburg, Augsburg, Germany
  • 12Institute of Applied Energy (IAE), Minato, Tokyo 105-0003, Japan
  • 13International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, 602 Duncan Drive, Auburn, AL 36849, USA
  • 14Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research/Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany
  • 15College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK
  • 16Department of Atmospheric Sciences, University of Illinois, Urbana, IL 61801, USA
  • deceased, 19 January 2021

Abstract. Satellite data reveal widespread changes of Earth's vegetation cover. Regions intensively attended to by humans are mostly greening due to land management. Natural vegetation, on the other hand, is exhibiting patterns of both greening and browning in all continents. Factors linked to anthropogenic carbon emissions, such as CO2 fertilization, climate change and consequent disturbances, such as fires and droughts, are hypothesized to be key drivers of changes in natural vegetation. A rigorous regional attribution at biome-level that can be scaled into a global picture of what is behind the observed changes is currently lacking. Here we analyze different datasets of decades-long satellite observations of global leaf area index (LAI, 1981–2017) as well as other proxies of vegetation changes, and identify several clusters of significant long-term changes. Using process-based model simulations (Earth system and land surface models), we disentangle the effects of anthropogenic carbon emissions on LAI in a probabilistic setting applying Causal Counterfactual Theory. The analysis prominently indicates the effects of climate change on many biomes – warming in northern ecosystems (greening) and rainfall anomalies in tropical biomes (browning). Our results do not support previously published accounts of dominant global-scale effects of CO2 fertilization. Altogether, our analysis reveals a slowing down of greening and strengthening of browning trends, particularly in the last two decades. Most models substantially underestimate the emerging vegetation browning, especially in the tropical rainforests. Leaf area loss in these productive ecosystems could be an early indicator of a slow-down in the terrestrial carbon sink. Models need to account for this effect to realize plausible climate projections of the 21st century.

Alexander J. Winkler et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-37', Anonymous Referee #1, 26 Feb 2021
  • CC1: 'Comment on bg-2021-37', Oliver Dilly, 06 Apr 2021
  • RC2: 'Comment on bg-2021-37', Christian Frankenberg, 19 Apr 2021

Alexander J. Winkler et al.

Video supplement

Leaf Area Changes of Sub-Saharan Africa Throughout the Satellite Era Michael Böttinger and Alexander J. Winkler

Alexander J. Winkler et al.


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Short summary
Satellite observations since the early 1980s show that Earth's greening trend is slowing down and that browning clusters are emerging, especially in the last two decades. A collection of model simulations in conjunction with causal theory points at climatic changes as a key driver of vegetation changes in natural ecosystems. Most models underestimate the observed vegetation browning, especially in tropical rainforests, which could be due to an excessive CO2 fertilization effect in models.