83
Long-Term Climate and Development Futures
Section 3
0
1000
500
1500
2000
2020
a) Carbon budgets and emissions
Lifetime emissions from fossil fuel 
infrastructure without additional abatement, 
if historical operating patterns are maintained
2020–2030 CO2 emissions 
assuming constant at 2019 level
1.5°C (>50% chance)
2°C (83% chance)
2°C (>67% chance)
Existing
Existing and
 planned
Historical emissions 1850-2019
2°C
(83%)
1.5°C
(>50%)
Carbon budgets
1000
0
2000
Remaining 
carbon budgets
diﬀerent emissions 
scenarios and their 
ranges of warming 
Remaining carbon budgets to limit warming to 1.5°C could 
soon be exhausted, and those for 2°C largely depleted
Remaining carbon budgets are similar to emissions from use of existing 
and planned fossil fuel infrastructure, without additional abatement
these emissions determine how 
much warming we will experience
Warming since 1850-1900
°C
Cumulative CO2 emissions (GtCO2) since 1850
Historical global
warming
SSP1-1.9
SSP1-2.6
SSP2-4.5
SSP3-7.0
SSP5-8.5
1000
2000
3000 
4000
4500
–0.5
0
0.5
1
1.5
2
2.5
3
historical
since 2020
Cumulative CO2 emissions (GtCO2)
this line indicates 
maximum emissions 
to stay within 2°C 
of warming (with 
83% chance)
Every ton of CO2 adds to global warming
b) Cumulative CO2 emissions and warming until 2050
Figure 3.5: Cumulative past, projected, and committed emissions, and associated global temperature changes.