Kate Calvin

1. Overshoot in Modelled
Pathways
Kate Calvin
NASA
Lead Author AR6 WGIII Chapter 3 – Mitigation pathways
compatible with long-term goals

2. • WGIII categorized pathways depending
on their likelihood of exceeding global
warming levels (at peak and in 2100).
• Limited overshoot: exceeding 1.5°C by up
to about 0.1°C and for up to several
decades
• High overshoot: temporarily exceeding
1.5°C by 0.1°C-0.3°C for up to several
decades
• WGI also assesses a pathway with higher
overshoot.
Overshoot pathways: Temperature Change
Data from WGIII Box SPM.1 Figure 1

3. Overshoot pathways: Implications for Emissions
Data from WGIII Figure 3.10
Data from WGIII Box SPM.1 Figure 1

4. Pathways with lower overshoot
include more rapid near-term
emissions reductions.
Overshoot pathways: Implications for Emissions
Data from WGIII Figure 3.10
Data from WGIII Box SPM.1 Figure 1

5. Overshoot pathways: Implications for Emissions
Pathways with higher overshoot
include more more net negative
emissions in the long-term.
Data from WGIII Figure 3.10
Data from WGIII Box SPM.1 Figure 1

6. The aggregate amount of carbon dioxide
removal used in a mitigation pathway is
larger than the total net negative CO2
emissions
• Cumulative net negative CO2
emissions are larger in pathways with
high overshoot (median 360 GtCO2)
than in pathways with no or limited
overshoot (median 220 GtCO2).
• Methods and levels of CDR
deployment in modelled pathways vary
depending on assumptions about
costs, availability, and constraints.
• The impacts, risks, and co-benefits of
CDR vary depending on the method,
context, and scale.
Overshoot pathways: Carbon Dioxide Removal
Data from WGIII Figure 3.10

7. Carbon Dioxide Removal and its
role in mitigation strategies
Oliver Geden
German Institute for International and Security Affairs (SWP)
Lead Author, AR6 WGIII Chapter 12 - Cross Sectoral Perspectives

8. • Global (& national)
pathways with basic
components
• Net-negative
emissions: gross
emissions minus
gross CO2 removals
(CDR)
• We are already doing
CO2 removal (via
LULUCF), but scale-
up for net-negative
CO2 mainly via novel
methods with longer
storage timescales
WGIII Chapter 12, Cross-Chapter Box 8, Figure 2
Net-negative means more carbon dioxide removal (CDR)

9. • Net-zero GHG is more
ambitious (and occurs
later) than net-zero
CO2, & with more CDR
• At point of net-zero
GHG, CO2 emissions
are already net-
negative
(residual CO2 and non-
CO2 emissions
balanced by CO2
removal)
WGIII Chapter 12, Cross-Chapter Box 8, Figure 2
Carbon dioxide removal under net-zero CO2 and net-zero GHG

10. • CDR: Anthropogenic
activities removing
CO2 from
atmosphere and
durably storing it in
geological, terrestrial,
or ocean reservoirs
• Assessment of costs
& potentials,
feasibility &
sustainability
constraints, risks &
co-benefits,
especially at (very)
large scales
• Methodologies for
monitoring, reporting
& verification (MRV)
of carbon flows
WGIII Chapter 12, Cross-Chapter Box 8, Figure 1
Broad variety of carbon dioxide removal methods, many unexplored