Box4. What are the temperature implications of present pledges?

It is not possible to precisely answer the above question because the trend in temperature will strongly depend on the pathway of emissions after 2020. But results from integrated assessment models give us a hint at the range of pathways that could occur between 2020 and 2100. If we start at the level of emissions expected from the Copenhagen Accord pledges in 2020 and then follow the range of these pathways through to 2100, we find that they imply a temperature increase of between 2.5 to 5°C before the end of the century (see Figure B). The lower bound is the case in which emissions are fairly stringently controlled after 2020, and the upper in which they are more weakly controlled. In other words, emission levels in 2020 implied by current pledges do not seem to be consistent with 2°C or 1.5°C temperature limits. To stay within these limits, emission levels would have to be lower in 2020 and then be followed by considerable reductions.

 

Figure A: Temperature increases associated with emission pathways and compared to the expected emissions from
the pledges: Coloured bands show groups of IAM emission pathways that have approximately the same likely avoided
temperature increase in the twenty-first century. Specifically the coloured bands show the 20th to 80th percentile range
of the IAM pathways associated with those temperature increases 15. Superimposed on top of the pathways is the
range of estimated emissions resulting from the Copenhagen Accord pledges. The small black bar shows the range
of median estimates from the four pledge cases. The thin blue bar represents the wider range of estimates associated
with those four cases (the 20th to 80th percentile range).

@Copyright

 

  15     The gaps between the coloured bands come about because this report mainly compiled pathways from low greenhouse gas stabilisation scenarios