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No projected global drylands expansion under greenhouse warming

Abstract

Drylands, comprising land regions characterized by water-limited, sparse vegetation, have commonly been projected to expand globally under climate warming. Such projections, however, rely on an atmospheric proxy for drylands, the aridity index, which has recently been shown to yield qualitatively incorrect projections of various components of the terrestrial water cycle. Here, we use an alternative index of drylands, based directly on relevant ecohydrological variables, and compare projections of both indices in Coupled Model Intercomparison Project Phase 5 climate models as well as Dynamic Global Vegetation Models. The aridity index overestimates simulated ecohydrological index changes. This divergence reflects different index sensitivities to hydroclimate change and opposite responses to the physiological effect on vegetation of increasing atmospheric CO2. Atmospheric aridity is thus not an accurate proxy of the future extent of drylands. Despite greater uncertainties than in atmospheric projections, climate model ecohydrological projections indicate no global drylands expansion under greenhouse warming, contrary to previous claims based on atmospheric aridity.

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Fig. 1: Establishing an EI of drylands in CMIP5 models.
Fig. 2: Divergent AI and EI projections under climate change in CMIP5 models.
Fig. 3: Different sensitivities of the EI and the AI to hydroclimatic changes.
Fig. 4: Plant physiology decouples AI and EI projections.
Fig. 5: Changes in drylands area in CMIP5 models under the AI and EI definitions.
Fig. 6: Changes in drylands in ISIMIP.

Data availability

All climate model simulations used in the Article are from CMIP5 and are publicly available—for instance, at https://esgf-node.llnl.gov/search/cmip5/. All ISIMIP simulations are freely available as well—for example, at https://esg.pik-potsdam.de/search/isimip/. All calculated data generated from these sources are available from the corresponding author upon request.

Code availability

The custom R code written to read and analyse the data and generate the figures is available on GitHub at https://doi.org/10.5281/zenodo.4490414 (ref. 51).

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Acknowledgements

We thank the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups (listed in Supplementary Table 1 of this paper) for producing and making available their model output. For CMIP, the US Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led the development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. For their roles in producing, coordinating and making available the ISIMIP input data and impact model output, we thank the modelling groups, the ISIMIP sector coordinators and the ISIMIP cross-sectoral science team for the Biomes sectors. K.A.M. acknowledges funding from a Winokur Seed Grant in Environmental Sciences from the Harvard University Center for the Environment.

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A.B. and K.A.M. designed the study. A.B. conducted the analysis and wrote the manuscript. K.A.M. advised on the interpretation of the results and contributed to the manuscript preparation.

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Correspondence to Alexis Berg.

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The authors declare no competing interests.

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Peer review information Nature Climate Change thanks Peter Greve, Congbin Fu and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Table 1, Discussions 1–3 and Figs. 1–14.

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Berg, A., McColl, K.A. No projected global drylands expansion under greenhouse warming. Nat. Clim. Chang. 11, 331–337 (2021). https://doi.org/10.1038/s41558-021-01007-8

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