Differential climate impacts for policy-relevant limits to global warming: the case of 1.5° C and 2° C
Creators: name: Schleussner, Carl-Friedrich
name: Lissner, Tabea K.
name: Fischer, Erich M.
name: Wohland, Jan
name: Perrette, Mahé
name: Golly, Antonius
name: Rogelj, Joeri
name: Childers, Katelin H.
name: Schewe, Jacob
name: Frieler, Katja
name: Mengel, Matthias
name: Hare, William L.
name: Schaeffer, Michiel
Publisher: name: ETH Zurich
Year: 2015

description: 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.  Currently,  two  such  levels  are  discussed  in  the  context  of the international climate negotiations as long-term global temperature goals: a below 2◦C  and  a  1.5◦C  limit  in  global-mean  temperature  rise  above  pre-industrial  levels.Despite the prominence of these two temperature limits, a comprehensive assessment 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 1.5◦C and 2◦C. 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  on wards.  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  several  hot-spots  of  change20emerge. 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% longer 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 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 under a 2◦C warming, which is about 10 cm lower for a 1.5◦C scenario. Our findings highlight the importance of regional differentiation to assess future climate risks as well as different vulnerabilities to incremental increases in global-mean temperature. The article provides a consistent and comprehensive assessment of existing projections and a solid foundation for future work on refining our understanding of warming-level dependent climate impacts.
description: Earth System Dynamics Discussions, 6
description: ISSN:2190-4995