Chris Jones
IPCC Lead Author, WGI Chapter 4
IPCC Synthesis Report Core Writing Team
Met Office Hadley Centre, Exeter, UK
UNFCCC COP27, Science for Climate Action Pavilion, 17th November 2022
CARBON BUDGETS
AND EARTH SYSTEM ASPECTS OF
CARBON DIOXIDE REMOVAL

• Amount of global warming is
proportional to the total
(“cumulative”) CO2 emissions
• Limiting global warming requires
limiting total emissions
• There is a finite amount
(“budget”) we can emit
before we reach a warming
level
• We had 500 GtCO2 left of our
1.5°C carbon budget
• from the start of 2020
• for a 50% chance
• Now reduced to 380 GtCO2
WGI Figure SPM.10
Every tonne of CO2 emissions adds to global warming

Remaining carbon budget is small
https://globalcarbonbudget.org/

Remaining carbon budget is small – required reductions very fast
https://globalcarbonbudget.org/

CDR is not a replacement for deep and rapid emissions reductions
• IPCC SR15 Fig SPM.3B
Vast majority of action
is emissions reduction
Small amount of CDR
for hard-to-abate
residual
Land-use term is net
of gross emissions
and gross removals in
AFOLU sector

CDR is happening already
•Deforestation is the main driver of land-use emissions (remaining high at 6.7 ± 1.5 GtCO2 per year for
2012-2021). Forest fluxes from re/afforestation and wood harvest emissions and removals
counterbalance approximately half of these emissions (-3.5 ± 1.0 GtCO2 per year).
6.7 ± 1.5
2012-2021 average Gt CO2 per year
-3.5 ± 1.0
0.6 ± 0.5
0.8 ± 0.3
Components of land-use change
emissions
https://globalcarbonbudget.org/

Scope and implications of different CDR techniques
AR6 WGI
assessment
Fig 5.36

Scope and implications of different CDR techniques
Storage
permanence?
decades to
many
millennia
AR6 WGI
assessment
Fig 5.36

Scope and implications of different CDR techniques
Storage
potential?
Some
techniques
may
sequester
multiple
GtCO2/yr
AR6 WGI
assessment
Fig 5.36

Scope and implications of different CDR techniques
Non-CO2?
Need full
GHG
assessment of
techniques
AR6 WGI
assessment
Fig 5.36

Scope and implications of different CDR techniques
Biophysical
effects?
AR6 WGI
assessment
Fig 5.36

Scope and implications of different CDR techniques
Other trade-
offs or co-
benefits?
Air/water
quality,
biodiversity
AR6 WGI
assessment
Fig 5.36

• We will need CDR
• Both for net-zero and
net-negative
• We’re doing it now on managed
land
• All aspects have
implications and costs
• Land
• Water
• Nutrients
• $$$
• No single technique can
solve this singly
• Devil is in the detail
• Full GHG accounting
• Biophysical effects
• Uncertainty in carbon budgets-
huge uncertainty in future need
for CDR – need emissions
reductions now
Climate system summary of CDR
• CDR is not / cannot be a replacement for emissions reduction