Table 1.

Summary of scenario pathway characteristics.

scenario pathwayglobal 21st century CO2 or greenhouse gas budget in GtCO2 or [GtCO2e]Annex 1 peak date/21st century cumulative emissions in GtCO2 or [GtCO2e]non-Annex 1 peak date/21st century cumulative emissions in GtCO2 or [GtCO2e]global peak dateAnnex 1 % reduction on 1990 levels by 2020 (2050)non-Annex 1 % reduction on 1990 levels by 2020 (2050)post-peak Annex 1 rate of reductionpost-peak non-Annex 1 rate of reductionpost-peak global rate of reduction (includes deforestation)approximate % of exceeding 2°C (based on 2000–2049 emissions using PRIMAP)
C+1132120072020201256% (98%)+1714% (54%)10–11%6–7%6–7%36%
313742
C+2a1321200720252007100% (100%)+193% (27%)6–7%6–7%
139916
C+3132120072025200756% (98%)+143% (54%)10–11%7–8%7–8%37%
313742
C+415782007202020196% (84%)+186% (45%)5–6%b5–6%5–6%50%
532780
C+5157820072025202044% (95%)+220% (32%)8%7–8%7–8%52%
363949
C+6a1578200720252024100% (100%)+220% (+38%)4–5%4–5%
1531159
B6 1a,c[1376]20072017201795% (95%)61% (61%)
[265][841]
B6c 2[2202]20102020201725% (82%)+135% (46%)4–6%5–6%3%39% (48%)d
[639][1293]
B6c 3[2202]200720252013–201857% (95%)+154% (24%)8–10%6–7%4–5%39% (48%)d
[429][1503]
B6c 4[2202]20072025201334% (90%)+111% (17%)6%4–5%4–5%38% (47%)d
[552][1380]
orthodox C+27412015203020272% (60%)+223% (+163%)3%3%3%88%
[729]1747
orthodox B6[3662]2015203020285% (62%)+180% (128%)3%3%3%88% (92%)d
[891][2501]
  • aThese scenario pathways are not viable as they could not remain within the carbon budget prescribed.

  • bThis is the reduction rate following the period of relatively stable emissions until 2016.

  • cAll B6 scenario pathways assume an ‘emission floor’ of 6GtCO2e for food-related emissions for an approximate 9 billion population post-2050 until 2100. If a different ‘emission floor’ were to be used, emission reduction rates would be altered for the same cumulative values.

  • dThe figure in brackets illustrates a higher probability to take into account the ongoing emissions associated with food production as opposed to greenhouse gas emissions tending to zero.