Royal Academy Engineering, London 4 Nov 2009 On 4 November the UK CCS Community network hosted a meetingWhat will it take to avoid dangerous anthropogenic interference in the climate system? And will they be talking about it in Copenhagen?

1. The trillionth tonne of carbon
Generate idealised CO2 emission scenarios varying:
– Initial rate of exponential growth from 2010 (1-3%/year).
What will it take to avoid dangerous anthropogenic – Year in which growth begins to slow down (2012 to 2050).
Rate at which growth slows and reverses.
interference in the climate system? –
Maximum rate of emission decline (up to -10%/year).
And will they be talking about it in Copenhagen? –
Aim to stabilize temperatures, not concentrations:
emission decline continues until temperatures peak.
Myles Allen
Simulate response using simple coupled climate
Department of Physics, University of Oxford carbon-cycle models constrained by observations.
myles.allen@physics.ox.ac.uk Use conventional IPCC-like distributions for e.g.
Thanks to: Niel Bowerman, David Frame, Chris climate sensitivity (no “post-AR4” science).
Huntingford, Chris Jones, Jason Lowe, Malte Identify properties of emission scenarios that
Meinshausen & Nicolai Meinshausen determine climate damages.
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Three scenarios, different timing, same total:
Examples of idealised emission scenarios
Cumulative emissions determine peak warming
Red and orange
scenarios all
represent
cumulative
emissions of one
trillion tonnes of
carbon From Allen et al, Nature, 2009
see also Meinshausen et al, Nature, 2009
Solomon et al, PNAS, 2009
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Emissions in 2020 only matter for peak warming Emissions in 2050 are a better indicator of total
insofar as they determine total emissions emissions, but it is the total that still matters
Colours Colours
show most show most
likely peak likely peak
warming warming
under under
different different
scenarios scenarios
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2. Total emissions to 2050 (WBGU proposal) also But peak emissions do matter for maximum
only matter as an indicator of the overall total CO2-induced rate of warming
Colours Colours
show most show most
likely peak likely peak
warming rate of
under warming
different
scenarios
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And peak emissions plus the cumulative total Peak warming is determined by total amount of
determine the required rate of reduction carbon released into the atmosphere
Colours
show peak
rate of
emission
reduction
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Why this matters What cumulative targets mean
In effect, CO2 accumulates in the atmosphere. Most Current global emissions about 10 GtC per year
other greenhouse gases do not. Cumulative emissions to date about 0.55TtC.
We need to limit cumulative emissions of carbon UKCCC target: ~1TtC, implies average future rate of
dioxide to avoid dangerous climate change. reduction of 2.5%/year if emissions peak now.
One trillion tonnes of carbon (1 TtC) implies a most WBGU proposal: 750GtCO22010-2050 0.75TtCTotal
likely warming of 2oC, with a 1- range of 1.6-2.6oC. implies average future rate of reduction of 5%/year.
Postponing emissions peak to 2020 does not
“commit us to 2oC”, it commits us to potentially
unfeasible rates of emission reductions after 2020 if
we are still to avoid 2oC.
The case for limiting cumulative CO2 emissions to
less than 1 TtC depends on conventional IPCC AR4
science, not on “new science”.
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3. The WBGU proposal: per capita emissions to The heart of the problem: how fossil fuel
stay within a 750GtCO2 2010-2050 budget reserves relate to atmospheric capacity
Past emissions
Conventional oil and gas coal
and unconventional reserves
oil, gas and
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Will emission “rationing” ever succeed? Stocks and flows of carbon
Emitting a given total amount of CO2 slower makes CO2-induced climate change is a stock problem: if
very little difference to the risk of dangerous we want to avoid 2oC warming, we must limit
anthropogenic interference in the climate. cumulative emissions to less than ~1TtC=1,000GtC.
To stay below 2oC, “safe” atmospheric capacity is All mitigation policies treat it as a flow problem: e.g.
~1TtC, half of which has already been emitted. 20/50% below 1990 emissions by 2020/2050 (GtC/y).
If we (arbitrarily) divide the atmospheric capacity by Measures to reduce the flow will only help as part of
the current fossil fuel mix, the carbon content of: a package to limit the cumulative stock.
– 15% of conventional oil gas reserves (60GtC) – Sequestering (burying) CO2 from coal plants makes sense,
– 95% of conventional coal reserves (2.3TtC) just substituting gas for coal does not.
– 100% of unconventional reserves (1.8TtC) – If we just focus on 2020 emissions, it is much cheaper to
substitute gas for coal than to sequester CO2.
needs to stay out of the atmosphere forever.
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Two approaches to managing stocks How can we ban people from using fossil fuels?
The Montreal Protocol. We can’t. The supply of economically viable fossil
– (a phased-in ban) energy is essentially limitless (~10x the amount we
The Common Fisheries Policy. can safely release into the atmosphere).
– (negotiated national quotas) So the risk of dangerous CO2-induced climate
change is determined by whether the net
sequestered fraction reaches 100% before we
release the trillionth tonne.
This does not mean all CO2 is captured, but any
remaining emissions must be offset by air capture.
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4. Smoothing the transition: the concept of SAFE
What SAFE carbon means in practice
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”?
– Emissions = (1-S) x Fossil carbon consumption
– In the very long term, S 100%.
– At present, S=0%.
A1 scenario: medium population, high growth, primary energy
Simplest option: S=C/C0:
supplies dominated by fossil fuels
– S = Sequestered fraction, including compensation for leaks.
A1T-R: Same population growth, much higher use of nuclear,
– C = Cumulative emissions from the time policy is adopted. gas and renewables.
– C0= Atmospheric capacity at the time policy is adopted. S tied to cumulative emissions, not time: rises automatically to
If all carbon sources were SaFE, we would never give the same emissions independent of consumption.
exceed the atmospheric capacity.
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But even if this were to be implemented
Dangerous fantasies
tomorrow…
Even if we limit total emissions to 1 TtC, that may be “We need a carbon price now”, either through cap-
too much. So we should be building a capacity for and-trade or a carbon tax.
negative emissions after 2050. No conceivable carbon price will stop all fossil fuel
Sequestration mandates linked to fossil fuel consumption.
extraction would be the fastest way to build capacity. We can’t solve the problem by making carbon more
expensive.
We must solve the problem by making carbon safe.
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