Summary of scenario pathway characteristics.
| scenario pathway | global 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 date | Annex 1 % reduction on 1990 levels by 2020 (2050) | non-Annex 1 % reduction on 1990 levels by 2020 (2050) | post-peak Annex 1 rate of reduction | post-peak non-Annex 1 rate of reduction | post-peak global rate of reduction (includes deforestation) | approximate % of exceeding 2°C (based on 2000–2049 emissions using PRIMAP) |
|---|---|---|---|---|---|---|---|---|---|---|
| C+1 | 1321 | 2007 | 2020 | 2012 | 56% (98%) | +1714% (54%) | 10–11% | 6–7% | 6–7% | 36% |
| 313 | 742 | |||||||||
| C+2a | 1321 | 2007 | 2025 | 2007 | 100% (100%) | +193% (27%) | — | 6–7% | 6–7% | |
| 139 | 916 | |||||||||
| C+3 | 1321 | 2007 | 2025 | 2007 | 56% (98%) | +143% (54%) | 10–11% | 7–8% | 7–8% | 37% |
| 313 | 742 | |||||||||
| C+4 | 1578 | 2007 | 2020 | 2019 | 6% (84%) | +186% (45%) | 5–6%b | 5–6% | 5–6% | 50% |
| 532 | 780 | |||||||||
| C+5 | 1578 | 2007 | 2025 | 2020 | 44% (95%) | +220% (32%) | 8% | 7–8% | 7–8% | 52% |
| 363 | 949 | |||||||||
| C+6a | 1578 | 2007 | 2025 | 2024 | 100% (100%) | +220% (+38%) | — | 4–5% | 4–5% | — |
| 153 | 1159 | |||||||||
| B6 1a,c | [1376] | 2007 | 2017 | 2017 | 95% (95%) | 61% (61%) | — | — | — | — |
| [265] | [841] | |||||||||
| B6c 2 | [2202] | 2010 | 2020 | 2017 | 25% (82%) | +135% (46%) | 4–6% | 5–6% | 3% | 39% (48%)d |
| [639] | [1293] | |||||||||
| B6c 3 | [2202] | 2007 | 2025 | 2013–2018 | 57% (95%) | +154% (24%) | 8–10% | 6–7% | 4–5% | 39% (48%)d |
| [429] | [1503] | |||||||||
| B6c 4 | [2202] | 2007 | 2025 | 2013 | 34% (90%) | +111% (17%) | 6% | 4–5% | 4–5% | 38% (47%)d |
| [552] | [1380] | |||||||||
| orthodox C+ | 2741 | 2015 | 2030 | 2027 | 2% (60%) | +223% (+163%) | 3% | 3% | 3% | 88% |
| [729] | 1747 | |||||||||
| orthodox B6 | [3662] | 2015 | 2030 | 2028 | 5% (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.