The role of carbon sequestration in reducing atmospheric CO 2

1. The role of carbon sequestration in reducing atmospheric CO2 Alicia Evans-Imbert

2. 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

3. 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

4. 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

5. 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 Storage Potential (GtC) Aquifers, if structural traps are needed 50 Aquifers, if structural traps are not needed 2700–13000 Enhanced oil recovery 20 Depleted oil fields 40–100 Depleted gas fields 90–400 Deep coal beds 100–300 Minimum total about 300

6. 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

7. 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%

8. 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

9. Scenario Conditions

10. 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

12. 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

15. 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

17. 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

18. 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.