text: 1.  Introduction 
  
  The majority of climate-change impacts assessments have tended to be framed in terms of future 
  time horizons, e.g. impacts by the middle or end of the twenty-ﬁrst century [1,2]. However, 
  with international climate policy now largely focused on limiting warming to speciﬁc levels of 
  global mean temperature such as 2°C [3] or 1.5°C [4], policy-relevant climate impacts assessments 
  increasingly need to be framed in terms of such warming levels. 
  There are two major research questions concerning the impacts of climate change at 1.5°C and 
  2°C global warming, which are relevant to both mitigation and adaptation policy areas. 
  
  (i) How much larger are the impacts at 2°C compared to 1.5°C? This is the primary question 
  arising from the Paris Agreement [4] and is relevant to mitigation policy, informing 
  judgements and actions on holding the global temperature rise to ‘well below 2°C’ and 
  ‘pursuing efforts to limit the temperature increase to 1.5°C’. 
  
  (ii) What regional climate conditions and related hydrological and ecological conditions 
  could occur at a particular level of global warming, such as 2°C? This is relevant to 
  adaptation policy and planning—exploring the possible outcomes for these levels of 
  warming will help facilitate adaptation and improved resilience to account for a 1.5°C or 
  2°C world. It is recognized that many adaptation decisions require information on timing 
  of speciﬁc impacts or risks, but nevertheless, framing regional impacts assessments in 
  terms of associated global warming levels (GWLs) may help provide context of the levels 
  of climate change that may be avoidable or unavoidable (and hence require adaptation). 