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Population-based emergence of unfamiliar climates


Time of emergence, which characterizes when significant signals of climate change will emerge from existing variability, is a useful and increasingly common metric1,2,3. However, a more useful metric for understanding future climate change in the context of past experience may be the ratio of climate signal to noise (S/N)—a measure of the amplitude of change expressed in terms of units of existing variability3. Here, we present S/N projections in the context of emergent climates (termed ‘unusual’, ‘unfamiliar’ and ‘unknown’ by reference to an individual’s lifetime), highlighting sensitivity to future emissions scenarios and geographical and human groupings. We show how for large sections of the world’s population, and for several geopolitical international groupings, mitigation can delay the onset of ‘unknown’ or ‘unfamiliar’ climates by decades, and perhaps even beyond 2100. Our results demonstrate that the benefits of mitigation accumulate over several decades, a key metric of which is reducing S/N, or keeping climate as familiar as possible. A relationship is also identified between cumulative emissions and patterns of emergent climate signals. Timely mitigation will therefore provide the greatest benefits to those facing the earliest impacts, many of whom are alive now.

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Figure 1: Emergence of climate change in idealized, geographical and population-weighted contexts.
Figure 2: Climate emergence under the RCP4.5 scenario.
Figure 3: Climate emergence under high-carbon and -mitigation scenarios.
Figure 4: Population exposure to unknown and unfamiliar climates.


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D.F., L.J.H. and M.J. acknowledge support from Victoria University of Wellington. E.H. and M.J. acknowledge support from NCAS Climate. D.F. and L.J.H. acknowledge support from the Deep South National Science Challenge. E.H. is funded by a UK NERC Research Fellowship. The authors thank S. Dean and S. Rosier for informative discussions.

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M.J. and D.F. conceived the project. D.F., E.H. and L.J.H. performed the analysis, and M.d.R. produced the cartograms and maps. All authors wrote the paper.

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Correspondence to Dave Frame.

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The authors declare no competing financial interests.

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Frame, D., Joshi, M., Hawkins, E. et al. Population-based emergence of unfamiliar climates. Nature Clim Change 7, 407–411 (2017).

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