1) The document discusses key findings around carbon dioxide removal (CDR) from the IPCC's Sixth Assessment Report (AR6). 2) AR6 defines CDR as activities that remove CO2 from the atmosphere and store it durably, including both natural and enhanced biological and geochemical sinks as well as direct air capture with storage. 3) AR6 assessed CDR methods and their effects, finding that feedbacks will determine CDR effectiveness in drawing down atmospheric CO2. Pathways in AR6 all involve some amount of CDR to balance residual emissions, but specific volumes depend on contextual factors.

1. Carbon Dioxide Removal to reach
net-zero and return from overshoot:
knowledge gaps and research priorities
C O P 2 8 , 6 D e c 2 0 2 3

2. IPCC AR6 Approach to
Carbon Dioxide Removal
O L I V E R G E D E N
V i c e - C h a i r A R 7 W o r k i n g G r o u p I I I
L e a d A u t h o r A R 6 W G I I I & C W T A R 6 S y n t h e s i s R e p o r t
C O P 2 8 , 6 D e c 2 0 2 3

3. AR6 Definition of
Carbon Dioxide Removal
Anthropogenic activities removing carbon
dioxide (CO2) from the atmosphere and
durably storing it in geological, terrestrial, or
ocean reservoirs, or in products.
It includes existing and potential anthropogenic
enhancement of biological or geochemical CO2
sinks and direct air carbon dioxide capture and
storage (DACCS), but excludes natural CO2 uptake
not directly caused by human activities.
I P C C A R 6 , C R O S S - W G G L O S S A R Y

4. • No CDR chapters in WG I & III (nor in SR1.5 + SRCCL)
• Differentiation betw. outcome of practices and results on
systems level (CO2 removal vs. net-negative emissions)
• Taxonomy (& terminology) avoids nature-based vs.
(hybrid vs.) techological classification of CDR methods
• Strong terminology guidance for WG III (CDR, NETs,
methods/options, net-negative, net-zero CO2 or GHG)
• Techno-economic analysis of 12 CDR methods,
scenarios, but also feasibility assessment, cost &
potentials, (empirically oriented) governance & policies
• From „CDR: yes or no?“ to „which CDR methods, by
whom, by when, at which volumes and in which ways?“

5. • Global & national
pathways share basic
components
• (Modelled) residual
emissions mainly non-
CO2 GHGs from
agriculture, but also
CO2 from industry,
aviation and land-use
• ‚Gross/Gross‘
perspective more
insightful than ‚net only‘
I P C C A R 6 W G I I I , C H A P T E R 1 2 , C R O S S - C H A P T E R B O X 8 , F I G U R E 2

6. • No total CDR volumes
until 2100 (mainly due
to scenario database
reporting standards
and methodologies)
• Even if there were total
CDR volumes, it
wouldn‘t make much
sense to say „IPCC
shows we need x Gt of
CDR by 2050“
• Numbers depend on
contextual factors, incl.
assumptions on
discount rate & residual
emissions, and core
mitigation strategies
(IMPs, overshoot)
I P C C A R 6 W G I I I
T A B L E 3 . 5
& F I G U R E 1 2 . 3

7. • Every ambitious
(illustrative) mitigation
pathway involves CDR
• Volumes and sectoral
composition of residual
emissions & CDR differ
across global IMPs
• Net LULUCF values
lowers volumes on both
sides of zero line
I P C C A R 6 W G I I I F I G U R E S P M . 5

8. • AR WGI assesses
CDR methods along
several dimensions
• Highlights
biogeochemical and
biogeophysical effects
and feedbacks of CDR
• Feedbacks determine
effectiveness of CDR
in drawing down CO2
from atmosphere
I P C C A R 6 W G I , C H A P T E R 5 , F I G U R E 3 6

9. • Taxonomy of CDR
methods based on
AR6 WG I, highlighting
removal process &
timescale of storage
• Often several
implementation options
per CDR method
• CCS and CCU can be
part of CDR methods,
with durable storage of
CO2 from biomass or
ambient air
• No dichotomy beyond
land vs. ocean-based
I P C C A R 6 W G I I I , C H A P T E R 1 2 , C R O S S - C H A P T E R B O X 8 , F I G U R E 1

10. IPCC AR6 WG III, Chapter 12, Table 12.6

11. • Synthesis Report focus on
overshoot: exceedance of
1.5°C in early 2030s and
possible return by 2100
• Limiting warming to 1.5°C
by 2100 with limited
overshoot requires net
negative CO2 emissions
• Drastically reducing net
emissions 2019-2030
(GHG: 43%, CO2: 48%)
not enough to avoid
exceeding 1.5°C
temporarily but only to
limit overshoot (to ~0.1°C)
I P C C A R 6 S Y R , F I G U R E 3 . 5

12. Panelists (and their role in AR6)
Kirsten Zickfeld, Lead Author (LA) SR1.5 and LA WG I
Stephanie Roe, LA WG III and Contributing Author (CA) WG II
Steve Smith, CA WG III
Detlef van Vuuren, LA WG III and Member Core Writing Team Synthesis Report
Chris Bataille, LA WG III