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Volume 7, issue 2 | Copyright
Earth Syst. Dynam., 7, 327-351, 2016
https://doi.org/10.5194/esd-7-327-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 21 Apr 2016

Research article | 21 Apr 2016

Differential climate impacts for policy-relevant limits to global warming: the case of 1.5 °C and 2 °C

Carl-Friedrich Schleussner1,2, Tabea K. Lissner1,2, Erich M. Fischer3, Jan Wohland2, Mahé Perrette2, Antonius Golly4,6, Joeri Rogelj3,5, Katelin Childers2, Jacob Schewe2, Katja Frieler2, Matthias Mengel1,2, William Hare1,2, and Michiel Schaeffer1,7 Carl-Friedrich Schleussner et al.
  • 1Climate Analytics, Friedrichstr. 231 – Haus B, 10969 Berlin, Germany
  • 2Potsdam Institute for Climate Impact Research, Potsdam, Germany
  • 3Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
  • 4GFZ German Research Centre for Geosciences, Potsdam, Germany
  • 5Energy Program, International Institute for Applied Systems Analysis, Laxenburg, Austria
  • 6University of Potsdam, Institute of Earth and Environmental Science, Potsdam, Germany
  • 7Wageningen University and Research Centre, Environmental Systems Analysis Group, Wageningen, the Netherlands

Abstract. Robust appraisals of climate impacts at different levels of global-mean temperature increase are vital to guide assessments of dangerous anthropogenic interference with the climate system. The 2015 Paris Agreement includes a two-headed temperature goal: "holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C". Despite the prominence of these two temperature limits, a comprehensive overview of the differences in climate impacts at these levels is still missing. Here we provide an assessment of key impacts of climate change at warming levels of 1.5°C and 2°C, including extreme weather events, water availability, agricultural yields, sea-level rise and risk of coral reef loss. Our results reveal substantial differences in impacts between a 1.5°C and 2°C warming that are highly relevant for the assessment of dangerous anthropogenic interference with the climate system. For heat-related extremes, the additional 0.5°C increase in global-mean temperature marks the difference between events at the upper limit of present-day natural variability and a new climate regime, particularly in tropical regions. Similarly, this warming difference is likely to be decisive for the future of tropical coral reefs. In a scenario with an end-of-century warming of 2°C, virtually all tropical coral reefs are projected to be at risk of severe degradation due to temperature-induced bleaching from 2050 onwards. This fraction is reduced to about 90% in 2050 and projected to decline to 70% by 2100 for a 1.5°C scenario. Analyses of precipitation-related impacts reveal distinct regional differences and hot-spots of change emerge. Regional reduction in median water availability for the Mediterranean is found to nearly double from 9% to 17% between 1.5°C and 2°C, and the projected lengthening of regional dry spells increases from 7 to 11%. Projections for agricultural yields differ between crop types as well as world regions. While some (in particular high-latitude) regions may benefit, tropical regions like West Africa, South-East Asia, as well as Central and northern South America are projected to face substantial local yield reductions, particularly for wheat and maize. Best estimate sea-level rise projections based on two illustrative scenarios indicate a 50cm rise by 2100 relative to year 2000-levels for a 2°C scenario, and about 10 cm lower levels for a 1.5°C scenario. In a 1.5°C scenario, the rate of sea-level rise in 2100 would be reduced by about 30% compared to a 2°C scenario. Our findings highlight the importance of regional differentiation to assess both future climate risks and different vulnerabilities to incremental increases in global-mean temperature. The article provides a consistent and comprehensive assessment of existing projections and a good basis for future work on refining our understanding of the difference between impacts at 1.5°C and 2°C warming.

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Short summary
We present for the first time a comprehensive assessment of key climate impacts for the policy relevant warming levels of 1.5 °C and 2 °C above pre-industrial levels. We report substantial impact differences in intensity and frequency of extreme weather events, regional water availability and agricultural yields, sea-level rise and risk of coral reef loss. The increase in climate impacts is particularly pronounced in tropical and sub-tropical regions.
We present for the first time a comprehensive assessment of key climate impacts for the policy...
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