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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 1.‎5oC 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 2.‎0oC 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 lowemission 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 decade but under 1.‎5 and 2oC conditions a century in the future.‎ We use the representative concentration pathway 2.‎6 (RCP2.‎6) to provide the model boundary conditions for the 1.‎5oC scenario, and a weighted combination of RCP2.‎6 and RCP4.‎5 for the 2oC scenario.‎

Authors: 
D.‎ Mitchell, K.‎ AchutaRao, M.‎ Allen, I.‎ Bethke, U.‎ Beyerle, A.‎ Ciavarella, P.‎ M.‎ Forster, J.‎ Fuglestvedt, N.‎ Gillett, K.‎ Haustein, W.‎ Ingram, T.‎ Iversen, V.‎ Kharin, N.‎ Klingaman, N.‎ Massey, E.‎ Fischer, C.‎ Schleussner, J.‎ Scinocca, Ø.‎ Seland, H.‎ Shiogama
E.‎ Shuckburgh, S.‎ Sparrow, D.‎ Stone, P.‎ Uhe, D.‎ Wallom, M.‎ Wehner, R.‎ Zaaboul
Year: 
۲۰۱۷
Publication type: 
Scientific Paper
Publication Source: 
Geoscientific Model Development
Volume/Chapter/Issue: 
۱۰
Page Number: 
۵۷۱–۵۸۳
ISBN: 
doi:10.‎5194/gmd-10-571-2017