My presentation at the "Third Annual Conference of the Transatlantic University Collaboration for Climate and Energy Law" on 28 April 2021 in Oslo https://www.jus.uio.no/nifs/english/research/events/2021/04-28-tucccel.html

1. The path to net-zero emissions
Glen Peters (CICERO Center for International Climate Research, Oslo, Norway)
Third Annual Conference of the Transatlantic University Collaboration for Climate and
Energy Law (Remote from Oslo, 28/04/2021)

2. 1Gt CO2 equals 1 billion tonnes CO2
Stylized figure
Temperature rise versus total CO2 emissions

3. 1Gt CO2 equals 1 billion tonnes CO2
Stylized figure
More CO2 emissions, higher temperature

4. 1Gt CO2 equals 1 billion tonnes CO2
Zero CO2 emissions, temperature rise stops
Stylized figure

5. 1Gt CO2 equals 1 billion tonnes CO2
Stylized figure
Zero CO2 emissions, temperature rise stops

6. • The global temperature will stop rising when CO2 emissions
reach zero (emissions & removals balance)
– This essentially defines the ‘carbon budget’
– CO2 is a cumulative pollutant
– Any emissions of CO2 causes permanent damage
• Non-CO2 emissions play an important, but smaller role
– Declining CH4 (methane) emissions leads to declining temperature
– N2O behaves more like CO2, but emissions are much smaller
The need for (net)-zero emissions

7. 1) Positive: Emissions by sources
(e.g., burning fossil fuels, cutting down forests)
2) Negative: Removals by sinks
(e.g., growing new forests, engineered removal of CO2 from the atmosphere)
Net: 1 + 2: Emissions by sources plus removals by sinks
What are ‘net-zero’ emissions?

8. Distributing a carbon budget over time

9. We have already emitted a lot of CO2, and thus we can only emit a little more to stay under 1.5°C (or 2°C).
1Gt CO2 equals 1 billion tonnes CO2
Emission pathways

10. We have already emitted a lot of CO2, and thus we can only emit a little more to stay under 1.5°C (or 2°C).
The brown area is a carbon budget of 580GtCO2 (consistent with 1.5°C in 2100).
1Gt CO2 equals 1 billion tonnes CO2
Emission pathways – zero emissions

11. There are likely sectors where it is too hard (or expensive) to get emissions to zero (leads to ‘residual emissions’)
Carbon dioxide removal (e.g., afforestation) can offset those emissions leading to ‘net-zero’ emissions
1Gt CO2 equals 1 billion tonnes CO2
Emission pathways with net-zero

12. If we (deliberately) allow CO2 emissions to decline slower in the short-term, we can ‘overshoot’ the carbon budget,
but then we must repay that ‘carbon debt’ by removing carbon from the atmosphere at a planetary scale.
1Gt CO2 equals 1 billion tonnes CO2
Emission pathways with overshoot
This scenario reaches the same
temperature in 2100 as the
others, but first exceeds the
temperature reaching a maximum
at the point of net-zero
Net-zero
Net-negative

13. A problem with ‘net-zero’ is that it is still necessarily to radically reduce fossil emissions in the short term…
It is not possible to ‘offset’ by emitting just as much (or a little less) and buying some Carbon Dioxide Removal
Emissions pathways to avoid

14. Emissions and removals

15. Some parts of the energy system are particularly difficult to decarbonize, including aviation, long-distance transport,
steel & cement production, and provision of a reliable electricity supply
Source: Davis et al (2018)
Can all emissions be eliminated?

16. Many sources of agricultural emissions are hard-to-mitigate, and short-lived pollutants can warm or cool
Most mitigation scenarios suggest that non-CO2 emissions will cause a warming to 2050 and then a cooling effect
Non-CO2 emissions
Sources: Unsplash, Unsplash, Pixabay, Shuttershock

17. Because of hard-to-mitigate (or too expensive-to-mitigate) sectors, Carbon Dioxide Removal (CDR) is likely needed
Some removals are needed to balanced with residual emissions, the required scale of CDR is an important discussion
Source: MCC Berlin
Carbon Dioxide Removal

18. Net-zero GHG emissions occur 10-20 years after net-zero CO2 emissions for 1.5°C pathways
Net-zero years are about 20 years later for likely below 2°C.
Source: Rogelj et al (2021)
Net-zero CO2 versus GHG emissions
Positive (residual)
Negative (CDR)

19. • Many countries are pledging for ‘net-zero’ emissions
– US, EU27 have pledged net-zero GHG emissions by 2050
– China has pledged net-zero CO2 emissions by 2060
• Rich countries should reach net-zero before the global
average:
– ~2075: Net-zero GHG emissions
– ~2050: Net-zero CO2 emissions
• Many loopholes in definitions
‘Net-zero’ at the country level

20. Solving global warming the easy way!

21. The climate problem is solved when
everyone
stops burning fossil fuels
(& stops cutting down forests)

22. Peters_Glen
cicero.oslo.no
cicerosenterforklimaforskning
glen.peters@cicero.oslo.no
Glen Peters