| 英文摘要: | Observational data show a continued increase of hot extremes over land during the so-called global warming hiatus. This tendency is greater for the most extreme events and thus more relevant for impacts than changes in global mean temperature. In the wake of the release of the Working Group I contribution to the 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5)1, much attention in the media and scientific community has been devoted to the so-called hiatus2, 3, 4. This identified 'pause' in the increase of global mean temperature has been ascribed to various possible causes: for example, internal climate variability, a minimum in solar energy output, heat uptake in lower ocean layers, increased stratospheric water vapour, emission reductions of ozone-depleting substances and methane, data sampling and/or stronger shifts to La Niña states4, 5, 6, 7, 8, 9, 10. Based on existing observational evidence, we highlight that the term pause, as applied to the recent evolution of global annual mean temperatures, is ill-chosen and even misleading in the context of climate change. Indeed, an apparently static global mean temperature can mask large trends in temperatures at both regional4 and seasonal11 scales. More importantly, it is land-based changes in extreme temperatures, particularly those in hot extremes in inhabited areas, that have the most relevance for impacts12. It seems only justifiable to discuss a possible pause in the Earth's temperature increase if this term applies to a general behaviour of the climate system, and thus also to temperature extremes. However, we show that analyses based on observational data13, 14 reveal no pause in the evolution of hot extremes over land since 1997. We focus on 'extreme extremes', whereby we first investigate the total land area affected by various exceedances of the number of warm days over the local 90th percentile respective to a given base period (see Supplementary Information for more details). Figure 1a shows the time series of the ratio of land area affected by an exceedance of 30 extreme warm days (ExD30) per year relative to the 1979–2010 average for the ERA-Interim13 and HadEX2 datasets14. The datasets agree well despite differences in spatial coverage and base periods (Supplementary Information). More importantly, they reveal a positive trend in ExD30 during the hiatus period. These results are further confirmed for other exceedance frequencies (for example, 50 or 10 excess extreme warm days per year, ExD50 and ExD10, respectively), and the largest trends are found for the highest — that is, the most extreme — exceedance frequencies (ExD50, Fig. 1b). Because of the shortness of the hiatus period, significance testing of the trends has limited relevance15. Still, over the 15-year period from 1997 to 2012, increases in ERA-Interim are significant at the 5% level (Mann-Kendall test). Furthermore, the two, mostly independent, observational datasets agree well regarding the overall tendencies in trends of temperature extremes (Fig. 1b).
This research was partly conducted during a sabbatical of S.I.S. at the ARC Centre of Excellence for Climate System Science (COECSS). S.I.S. and B.M. acknowledge partial funding from the European Commission's 7th Framework Programme, under grant agreement 282672, EMBRACE project. M.G.D. and L.V.A. acknowledge funding through the Australian Research Council grants CE110001028 and LP100200690.
Affiliations
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the Institute for Atmospheric and Climate Science, ETH Zürich, 8057 Zürich, Switzerland
- Sonia I. Seneviratne &
- Brigitte Mueller
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Climate Change Research Centre, University of New South Wales, Sydney NSW 2052, Australia
- Markus G. Donat &
- Lisa V. Alexander
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ARC Centre of Excellence in Climate System Science, University of New South Wales, Sydney NSW 2052, Australia
- Markus G. Donat &
- Lisa V. Alexander
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Environment Canada, Climate Research Division, Toronto M3H 5T4, Canada
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