There has recently been interest in understanding the differences between specific levels of global warming, especially the Paris Agreement limits of 1.5 °C and 2 °C above pre-industrial levels. However, different model experiments1,2,3 have been used in these analyses under varying rates of increase in global-average temperature. Here, we use climate model simulations to show that, for a given global temperature, most land is significantly warmer in a rapidly warming (transient) case than in a quasi-equilibrium climate. This results in more than 90% of the world’s population experiencing a warmer local climate under transient global warming than equilibrium global warming. Relative to differences between the 1.5 °C and 2 °C global warming limits, the differences between transient and quasi-equilibrium states are substantial. For many land regions, the probability of very warm seasons is at least two times greater in a transient climate than in a quasi-equilibrium equivalent. In developing regions, there are sizable differences between transient and quasi-equilibrium climates that underline the importance of explicitly framing projections. Our study highlights the need to better understand differences between future climates under rapid warming and quasi-equilibrium conditions for the development of climate change adaptation policies. Yet, current multi-model experiments1,4 are not designed for this purpose.
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All model data used in this study are available in several public repositories, for example at https://esgf-node.llnl.gov/projects/esgf-llnl/. The model data used here were stored on the Australian node of the Earth System Grid (the National Computational Infrastructure). Population and GDP data were downloaded from the Global Carbon Project (http://www.cger.nies.go.jp/gcp/population-and-gdp.html). The figures used in this analysis are available at https://zenodo.org/record/3471030#.XaVve-gzbIU (https://doi.org/10.5281/zenodo.3471029). Raw figure data are provided at https://melbourne.figshare.com/articles/Source_figures_for_publication_on_transient_and_equilibrium_climate_change/10250954. Assistance using the figures is available from the corresponding authors.
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We thank R. Knutti for discussions. We acknowledge the support of staff at the NCI facility in Australia and staff at the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups 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. A.D.K. is funded through an Australian Research Council Discovery Early Career Researcher Award (DE180100638); T.P.L. through the Australian Research Council Centre of Excellence for Climate Extremes (CE170100023); and B.J.H. through an Australian Research Council Linkage project (LP150100062).
Peer review information Nature Climate Change thanks Daithi Stone and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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King, A.D., Lane, T.P., Henley, B.J. et al. Global and regional impacts differ between transient and equilibrium warmer worlds. Nat. Clim. Chang. 10, 42–47 (2020). https://doi.org/10.1038/s41558-019-0658-7
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