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Cumulative carbon and its implications: the
case for mandatory sequestration
Myles Allen
School of Geography and the Environment/ECI &
Department of Physics
University of Oxford
A career in climate research…
Matriculation
A career in climate research…
Awarded DPhil
A career in climate research…
IPCC Author
A career in climate research…
Lectureship
A career in climate research…
Chair
What happens to the carbon we dump into the
atmosphere?
Understanding the carbon cycle
A popular myth:
– “About half the carbon we dump in the atmosphere is taken
up by the oceans and biosphere, so if we reduce emissions
by 50%, concentrations will stop rising.” Right?
– Sadly, wrong.
Additional CO2 is rapidly mixed between the
atmosphere, near-surface oceans and biosphere, but
concentrations are rising in all three “pools.”
– Fraction removed by permanent carbon sinks is very small.
How various greenhouse gases behave after
emissions cease
So fossil carbon accumulates in the climate
system, and temperatures keep rising
And most of the warming over the past 50 years
is attributable to rising greenhouse gases
Human-
induced
warming
And the solution is…
Stock of cumulative CO2 emissions are the
principal determinant of peak warming
Which is not the topic of climate change
negotiations
What they obsess over
Which is not the topic of climate change
negotiations
What
actually
matters
Does this mean we can relax?
The risk of dangerous climate change is principally
driven by cumulative emissions of CO2.
To limit warming to 2oC, we need to limit the total
stock of carbon released to about 1TtC.
Reducing the rate of flow doesn’t help unless it is a
means of limiting the total stock.
Emissions from fossil fuels and deforestation since
1750 are about 0.5TtC.
On current trends, emissions reach 1TtC in 2040s.
So, we’ve got 30 years to relax?
Sadly, no: because CO2 accumulates, and can’t
be switched off, delay actually does matter
Impact of delay in reducing CO2 emissions
Committed CO2-induced warming at 2oC/TtC
1990 2000 2010 2020 2030 2040 2050Year
0
5
10
15
20
Glo
ba
l e
mis
sio
ns, fo
ssil
& lan
d-u
se
, (G
tC/y
r) 5.4oC5.0oC
4.6oC4.2oC
3.8oC3.4oC
3.0oC
Rate of decline after peak: 1.1%/yr
Conventional and unconventional reserves
There is plenty of fossil carbon down there
Past emissions, fossil and land-use changeConventional oil and gasConventional oil, gas and coal
Can we actually stop people from using fossil
fuels? And do we have any right to anyway?
Wit
h a
po
log
ies t
o C
harl
ton
Hesto
n
The problem with the Kyoto/Copenhagen short-
term emission budget approach
Emission rates in 2020 do not
determine peak warming.
Cheapest technologies for
getting emissions down in the
short term may crowd out
measures required to limit
cumulative emissions.
Kyoto and Wallace’s Technotrousers:
Prins & Rayner, 2008
Climate Mitigation with No New Taxes:
SAFE carbon
Sequestered Adequate Fraction of Extracted (SAFE)
carbon: carbon from a supply that ensures we never
exceed the atmospheric capacity.
So, what is an “Adequate Fraction”?
– S = net carbon sequestered / carbon extracted
– In the very long term, S→100%.
– At present, S=0%.
Simplest option: specify S=C/C0:
– C = Cumulative emissions from the time policy is adopted.
– C0= Atmospheric capacity at the time policy is adopted.
If all carbon sources were SAFE, we would never
exceed the atmospheric capacity.
Getting from A to B
A
B
Why carbon taxes are not the answer: waiting for
a high enough carbon price for CCS to be viable
IWG
Th
ea
tre
Gu
ild
Suppose the fossil fuel industry decides to
defend its share of world energy supply
But paying for all that sequestration implies a
carbon price, passed on to consumers
So they might consume less, making the carbon
price lower – but without compromising policy
Comparing SAFE carbon with IEA BLUE Map
scenario
S=40% in
2050 under
IEA BLUE
Map scenario
We could start with an optimistic (high) budget,
and adjust when warming reaches 1.5oC.
0.6 0.8 1.0 1.2 1.4Emissions to date (TtC)
0.0
0.2
0.4
0.6
0.8
1.0
Seq
ue
ste
red
fra
ction
a) SAFE carbon pathways
1.2%/10GtC
3.5%/10GtC
2000 2020 2040 2060 2080 2100Year
0
5
10
15
20
GtC
pe
r yea
r
b) High consumption scenario
2000 2020 2040 2060 2080 2100Year
0
5
10
15
20
GtC
pe
r yea
r
c) Low consumption scenario
Mandatory sequestration works
Gorgon gas project, Western Australia
Policy implications
Simple climate policy goal: to achieve 100% net
sequestration before we release the trillionth tonne.
– Purpose is clear.
– Progress is verifiable.
Complex energy strategy response:
– Rapid and immediate large-scale development of CCS.
– Cost of carbon determined by cost of CCS, not by politics.
– Potential windfall for owners of large point sources of CO2.
– Prepare for rising cost of carbon by phasing out fossil
subsidies, deploying renewables, nuclear, efficiency etc.
One policy, one outcome, no new taxes.
IT’S CUMULATIVE
CARBON,
STUPID
IT’S CUMULATIVE
CARBON,
STUPID