23 Mar 2022
23 Mar 2022
Status: this preprint is currently under review for the journal BG.

Bioclimatic change as a function of global warming from CMIP6 climate projections

Morgan Sparey1, Peter Cox1, and Mark Williamson1,2 Morgan Sparey et al.
  • 1College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QF, UK
  • 2Global Systems Institute, University of Exeter, Exeter, EX4 4QE, UK

Abstract. Climate change is predicted to lead to major changes in terrestrial ecosystems (Pörtner et al., 2022). However, significant differences in climate model projections for given scenarios of greenhouse gas emissions (Masson-Delmotte et al., 2021), continue to hinder detailed assessment. Here we show, using a traditional Köppen-Geiger bioclimate classification system (Köppen, 1884), that the latest CMIP6 Earth System Models actually agree very well on the fraction of the global land-surface that will undergo a significant change per degree of global warming. Data from ‘historical’ and ‘ssp585’ model runs are used to create bioclimate maps at various degrees of global warming, and to investigate the performance of the ensemble mean when classifying climate data into discrete categories. Using a streamlined Köppen-Geiger scheme with 13 classifications, global bioclimate classification maps at 2 K and 4 K of global warming above a 1901–1931 reference period are presented. These projections show large shifts in bioclimate distribution, with an almost exclusive change from colder, wetter bioclimates to hotter, dryer ones. Historical model run performance is assessed and examined by comparison with the bioclimatic classifications derived from the observed climate over the same time period. The fraction (f ) of the land experiencing a change in its bioclimatic class as a function of global warming (∆T ) is estimated by combining the results from the individual models. Despite the discrete nature of the bioclimatic classification scheme, we find only a weakly-saturating dependence of this fraction on global warming f = 1 − e −0.17∆T , which implies about 12 % of land experiencing a significant change in climate, per 1 K increase in global mean temperature between the global warming levels of 1 and 3 K. Therefore, we estimate that stabilising the climate at 1.5 K rather than 2 K of global warming, would save over 7 million square kilometres of land from a major bioclimatic change.

Morgan Sparey 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-2022-74', Anonymous Referee #1, 22 Apr 2022
    • AC1: 'Reply on RC1', Morgan Sparey, 06 Jul 2022
  • RC2: 'Comment on bg-2022-74', Anonymous Referee #2, 13 May 2022
    • AC2: 'Reply on RC2', Morgan Sparey, 06 Jul 2022

Morgan Sparey et al.

Morgan Sparey et al.


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Short summary
Accurate climate models are vital for mitigating climate change; however, projections often disagree. Using a Köppen-Geiger bioclimate classification system we show that CMIP6 climate models agree well on the fraction of global land-surface that will change classification per degree of global warming. We find that 12 % of land will change climate per degree of warming between 1 and 3 K, thus, stabilising warming at 1.5 rather than 2 K would save over 7 million km2 of land from bioclimatic change.