8rsta.royalsocietypublishing.orgP h i l .T r a n s .R .S o c .A376:20160452 ........................................................
Table3. TimeofreachingGWLsof1.5 °Cand2 °CintherawoutputfromtheHadGEM3climatesimulations,drivenbydifferent
setsofCMIP5sea-surfacetemperatures.Thedatesarethecentreyearofa20-yearperiodforwhichtheclimatedataareapplied
tothecalculationoftheClimPACTindices.
drivingSSTs 1.5 °C2 . 0 °C
IPSL-CM5A-LR 2015 2030
......................................... ............................................ .......................................... ..................................... ......................................
GFDL-ESM2M 2040 2055
......................................... ............................................ .......................................... ..................................... ......................................
HadGEM2-ES 2027 2039
......................................... ............................................ .......................................... ..................................... ......................................
IPSL-CM5A-MR 2020 2034
......................................... ............................................ .......................................... ..................................... ......................................
MIROC-ESM-CHEM 2023 2035
......................................... ............................................ .......................................... ..................................... ......................................
ACCESS1–0 2034 2046
......................................... ............................................ .......................................... ..................................... ......................................
up to present-day plus model-projected warming thereafter ( table 4 ). While this does lead to
inconsistent deﬁnitions of dates of the GWLs for applications of the climate model output with
and without bias correction, the focus here is on the level of warming relative to pre-industrial
rather than the timing of this warming. Therefore, priority is given to an accurate quantiﬁcation
of GWLs in all parts of the study, at the expense of inconsistencies in the dates of these warming
levels. The inconsistency between the dates of the GWLs ranged from 2 to 9 years depending on
the model and warming level. This inconsistency would have consequences if these results were
applied to time-dependent impacts and adaptation assessments, but that is not the case here so
this concern does not apply. However, one issue is that the time-dependent nature of the aerosol
forcing means that the spatial pattern of regional climate responses varies over time, so this will
lead to some degree of inconsistency between the analysis of the ClimPACT extremes and the
HCVI and JULES impacts projections.
3. Results
For a world at 2°C global warming, we present a range of outcomes to provide insight into the
level of agreement between models for a particular projected change, and hence an indication
of potential robustness of the projected changes for informing adaptation. We then make a
comparison of impacts at global warming 1.5°C to investigate the level of impact that would
be avoided by limiting global warming to different levels. Bearing in mind the uncertainty in
regional climate outcomes, we address this in a number of ways. For individual realizations, we
compare the impacts at different warming levels to see if they are systematically smaller at 1.5°C,
even if the sign of the change is uncertain. We also compare the range of outcomes at different
GWLs, to see if the regional-scale uncertainty itself increases with global warming.
(a) Climate-changeimpactsat2 °Cglobalwarming
For 2°C global warming, the ensemble-mean increase in annual daily maximum temperature was
above 2°C for most of the land surface, with the exception of the Indian subcontinent, most of