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The role of carbon
sequestration in reducing
atmospheric CO2
Alicia Evans-Imbert
Overview
 Article reviewed by L.D. Danny Harvey, 2004 titled:
Declining temporal effectiveness of carbon sequestration: implications for
compliance with the United National Framework Convention on Climate
Change
 CO2 emissions continue to increase along with the need to curb its effect, so
many have looked in the possible aid of carbon sequestration
 Article:
 Determines least damaging range of CO2 concentrations
 Calculates possible future emission levels
 Tracks likely temperature changes
 Evaluates sequestration levels
 Overall determines long-term effects of sequestration as a source of
negative emissions
Sequestration
 Natural carbon sinks cannot stop rise in CO2, sequestration could stabilize
atmospheric CO2 concentrations
 Carbon sequestration involves isolating carbon from other combustion
products of fuel or biomass, then compressing and transporting, finally
injecting into the site
 Best to use large centralized facilities that capture and transport carbon but
limits capture to 1/3 of emissions
 Capturing CO2 takes 10% increase in fuel use by these power plants to
have les than 90% capture
 Possible to capture CO2 with less energy from production of hydrogen
through gasification of coals or biomass
Sequestration Sites
 Sites of sequestration: depleted or existing oil and gas fields, deep aquifers
(uncertain of storage in aquifers without leakage), coal beds, and deep
ocean ( 3000m)
 Ocean can hold thousands of GtC of CO2, only 85% will remain
 Reliance on deep oceans for storage leads to increase in CO2 in
atmosphere and changes in ocean chemistry over thousands of years
 Sequestration in terrestrial aquifers and oil or gas fields may be limited to
300 GtC, although would have long term leakage
 However sequestration could still be a partial substitute for fossil fuel
reductions
Site storage potential
Table I
Estimates of the global carbon sequestration potential, excluding deep ocean disposal.
Based on summaries presented in Parson and Keith (1998) and Williams et al. (2000).
Reservoir
Aquifers, if structural traps are needed
Aquifers, if structural traps are not needed
Enhanced oil recovery
Depleted oil fields
Depleted gas fields
Deep coal beds
Minimum total about
Storage Potential (GtC)
50
2700–13000
20
40–100
90–400
100–300
300
UNFCCC
 UNFCCC is a document signed and ratified by 182 countries
 They agree that CO2 concentrations should stay at a level to avoid
“dangerous anthropogenic interference with the climate system” as of 1992
 Change should not be too large so that ecosystems can be allowed to adapt
 The production of food should not be threatened
 Economic development should occur in sustainable manner
 Author suggest that the document makes indirect value judgments that
deem ecosystems valuable without economic value to humans
CO2 Concentration Range
 Range depends on:
 increase in non-CO2 Green House Gases (GHG)
 relationship of concentrations and time-dependent climatic change
 relationship between climatic change and a range of key impacts
 Refers to Third Assessment Report of Intergovernmental Panel on Climate
Change (IPCC) for discussion of CO2 range issues
 Concludes compliance range for UNFCCC should be 350-450 ppmv
 CO2 near 450ppmv negative effects on marine productivity
 450ppmv associated with 0.2 decrease in ocean pH, and decrease of
surface CaCO3 saturation by 25%
Temperature Range
 Likely temperature changes based on range: 2-4°C based on models and
past changes but cannot rule what larger variance of 1-5°C
 With CO2 doubling minimum warming is 1°C, If things stay the same then
likely more then 1°C change
 Double CO2 climate shows 10-20% decrease in agricultural yields
 Even slight differences in temperature increase can be significant
 estimates show a dramatic increase of people at risk of hunger, water
shortage, malaria and flooding when change 2°C as compared to 1°C
 4°C warming causes: melting of Greenland ice sheet, collapse of artic
sheet, 10m sea level rise in 1000 years, and damaging forest ecosystems
Scenario Conditions
Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
High population
High population
High population
Low population
N/A
High GDP
growth
High GDP
growth
High GDP
growth
Low GDP
growth
N/A
N/A
1%/yr energy
2%/yr energy
2%/yr energy
2%/yr energy
intensity decline intensity decline intensity decline intensity decline
0.5%/yr growth
of carbon-free
power
0.5%/yr growth
of carbon-free
power
2%/yr growth of
carbon-free
power
2%/yr growth of
carbon-free
power
N/A
Emission Scenarios
 Emissions based on:
 population (P)
 economic output (dollars) per person ($/P)
 average primary energy consumption (joules) per dollar of economic
output (J/S)
 average CO2 emission per joule of primary energy consumption (E/J)
 Emission = P x ($/P) x (J/S) x (E/J)





Scenario1: CO2 6.5 GtC/yr in 2000 10 27GtC/yr 2100
Scenario 2: CO2 peak 9 GtC/yr in 2060 then decline to 7 GtC/yr by 2100
Scenario 3: CO2 peak 7.7 GtC/yr in 2030 then decline to 0 GtC by 2100
Scenario 4: CO2 decline from 6.9 GtC/yr in 2005 then decline to 0 by 2075
Scenario 5: N/A
Temperature & CO2 Scenarios
 Climate model used to translate emissions to CO2 then temperature
change, because amount of CO2 sequestration depends on climate
sensitivity; higher sensitivity lead to larger warming
 CO2 scenarios: concentration by year 2200
 1. 1395-1460 ppmv
 2. 660-700 ppmv
 3. 480-520 ppmv
 4. 425-450 ppmv
 5. 428-435 ppmv
 Temperature scenarios: sensitivity ∆T=2.0°C and ∆T=4.0°C
 1. peaks ~ 5.5 and 10.5°C
 2. peaks ~ 3.5 and 7.1°C
 3. peaks ~ 2.8 and 5.9°C
 4. peaks ~ 2.5 and 5.1°C
 5. peaks ~ 1.8 and 3.2°C
Potential Sequestration
 An impulse response is the reaction to sudden injection of CO2 into the
atmosphere and the ocean
 Injection into atmosphere, after 200yrs 70% is taken up by ocean and in
2000yrs 87%
 Injection in ocean, same proportions as atmosphere injection due to carbon
escaping into atmosphere
 When sequestration of 100 GtC over 100 yrs in terrestrial or ocean, CO2
reduced by 10ppmv (20GtC) or possible max of 23ppmv (46 GtC)
 To stabilize 350ppmv, 1 GtC/yr geological seq. for 200 yrs & 1 GtC in ocean
for 100yrs; higher temp sensitivity then increase to 2 GtC/yr geological
 If CO2 allowed to reach a peak of 517ppmv (or 356GtC above optimum)
then need to seq. 600GtC over 200 yrs to reduce to 368ppmv
 In order to sequester CO2 needs to be captured, the levels needed to keep
sequestration rates up and CO2 concentrations down might not be achieved
Concerns
 Local effects of injections on biota of concern
 Large amounts of ocean sequestration not good for environment
 Not clear if sequestration rate maintained after fuels phased out
 Benefits of seq. rapidly reduce over time even without leakage
 Necessary sequestration might require geological formations to be used to
capacity (~300GtC) and oceans to 100-200GtC even with aggressive
emissions reductions
 Additional sequestration could be possible in soils; a possible 5.7GtC to
8.7GtC
Conclusions
 Impacts of change are unknown, it is believed that beyond 450ppmv there
are serious threats; upper limit of 450ppmv is sound
 Believes UNFCCC should develop framework to stabilize CO2 at less than
450ppmv
 Reduction in fossil fuel use (~0 during century) and seq. of 1-2 GtC/yr for
the next century to have “option” of peaking no more then double CO2
climate
 Sequestering the same as not releasing at all; emission reductions
necessary
 Sequestration and fossil fuel reduction together best option
 Although no possible way of avoiding warming, avoiding sea level rise,
changes in oceanic circulation and a quicker recovery if temperature
increase is short are all possible.