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Title: Half a degree additional warming, prognosis and projected impacts (HAPPI): background and experimental design

The Intergovernmental Panel on Climate Change (IPCC) has accepted the invitation from the UNFCCC to provide a special report on the impacts of global warming of 1.5 °C above pre-industrial levels and on related global greenhouse-gas emission pathways. Many current experiments in, for example, the Coupled Model Inter-comparison Project (CMIP), are not specifically designed for informing this report. Here, we document the design of the half a degree additional warming, projections, prognosis and impacts (HAPPI) experiment. HAPPI provides a framework for the generation of climate data describing how the climate, and in particular extreme weather, might differ from the present day in worlds that are 1.5 and 2.0 °C warmer than pre-industrial conditions. Output from participating climate models includes variables frequently used by a range of impact models. The key challenge is to separate the impact of an additional approximately half degree of warming from uncertainty in climate model responses and internal climate variability that dominate CMIP-style experiments under low-emission scenarios.Large ensembles of simulations (> 50 members) of atmosphere-only models for three time slices are proposed, each a decade in length: the first being the most recent observed 10-year period (2006–2015), the second two being estimates of a similar decademore » but under 1.5 and 2 °C conditions a century in the future. We use the representative concentration pathway 2.6 (RCP2.6) to provide the model boundary conditions for the 1.5 °C scenario, and a weighted combination of RCP2.6 and RCP4.5 for the 2 °C scenario.« less
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  1. Oxford Univ., Oxford (United Kingdom); Univ. of Bristol, Bristol (United Kingdom)
  2. Indian Institute of Technology Delhi, New Delhi (India)
  3. Oxford Univ., Oxford (United Kingdom)
  4. Bjerknes Centre for Climate Research, Bergen (Norway)
  5. ETH Zurich, Zurich (Switzerland)
  6. Met Office Hadley Centre for Climate Science and Services, Exeter (United Kingdom)
  7. Univ. of Leeds, Leeds (United Kingdom)
  8. Center for International Climate and Environmental Research - Oslo (CICERO), Oslo (Norway)
  9. Univ. of Victoria, Victoria, BC (Canada)
  10. Oxford Univ., Oxford (United Kingdom); Met Office Hadley Centre for Climate Science and Services, Exeter (United Kingdom)
  11. Norwegian Meteorological Institute, Oslo (Norway)
  12. Univ. of Reading, Reading (United Kingdom)
  13. Climate Analytics, Berlin (Germany); Potsdam Institute for Climate Impact Research, Potsdam (Germany)
  14. National Institute for Environmental Studies, Ibaraki (Japan)
  15. British Antarctic Survey (BAS), Cambridge (United Kingdom)
  16. Univ. of Oxford, Oxford (United Kingdom)
  17. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  18. International Center for Biosaline Agriculture, Dubai (United Arab Emirates)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Geoscientific Model Development (Online)
Additional Journal Information:
Journal Name: Geoscientific Model Development (Online); Journal Volume: 10; Journal Issue: 2; Journal ID: ISSN 1991-9603
European Geosciences Union
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
OSTI Identifier: