Long-term Effectiveness of Dif-ferent Types of CO2 Sequestra-tion

Increasing levels of CO2 in the earth’s atmosphere are causing changes to the climate on a global scale.  Methods have been proposed to reduce the amount of carbon in the atmosphere as well as to decrease the amount of new carbon emissions being released.  Carbon capture and storage has become a prominent proposal for collecting CO2 from industrial outputs and sequestering them in various places.  Many methods and locations have been proposed for carbon storage.  Shaffer (2010) has researched and predicted the long-term effectiveness and consequences of different storage techniques, including deep ocean sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–>, onshore geological storage, and deep-ocean sediment storage.  He compared these to a “business-as usual” emissions model, based on projections if no changes are made to current practices, and to a desirable future emissions model, which is the ‘best-case’ scenario for avoiding strong global warming.  All the projections are drawn out to 50,000 A.D.  Shaffer found that these methods offer short term solutions, because CO2 is leaked and reintroduced into the atmosphere causing a delayed global warming effect.  He concludes that the best way to free ourselves and future generations of this climate burden is to dramatically reduce emissions now.—Anna Fiastro
Shaffer, G. 2010. Long-term effectiveness and consequences of carbon dioxide sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–>. Nature Geoscience. DOI:10.1030/NGEO0896.

Shaffer used the IPCC<!–[if supportFields]> XE “Intergovernmental Panel on Climate Change (IPCC)” <![endif]–><!–[if supportFields]><![endif]–> SRES model for the ‘business–as-usual’ and ‘best-case’ scenarios, and the Danish Center for Earth System Science (DCESS) model to make the long-term projections for the onshore and offshore scenarios. He compares the partial pressure of atmospheric CO2, the geologically stored CO2, the mean atmosphere and ocean warming, ocean carbon inventory change, and the ‘dead zone’ volume fraction of each method for the 50,000-year time scale.  The change in pH and change in CO2 was also predicted at the oceans surface and at 3,000 meters depth, for each scenario. 
The ‘business-as-usual’ scenario had the highest CO2 partial pressure and the most atmospheric and ocean warming for all that scenarios and the peaks in all three of these categories were the earliest on the time scale.  This is to be expected because it does not involve any attempt to reduce the CO2 emissions or their effects.  This scenario also resulted in the highest fraction of global ocean volume to be considered a dead zone, meaning that there would be very little oxygen dissolved in the water to support life.  “Business-as-usual” had a dramatic effect in the amount of carbon in the surface layers of the ocean, but did not have the greatest overall change in the amount of carbon in the ocean.  In this category it was overshadowed by the deep-ocean sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–>.  This analysis shows that some action should be taken in the face of increasing atmospheric carbon levels. 
In deep-ocean sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–>, CO2 is pumped into the cold, lower layers of the ocean that do not readily mix with the upper layers.  In the long term this method for storing carbon has similar effects as the “business-as-usual” on atmospheric partial pressure of CO2, atmospheric and oceanic warming, and the fraction of the ocean that is a “dead zone,” but not until 2,000 years later.  Then the ocean becomes mixed sufficiently to release the sequestered CO2 to the atmosphere.  Since in this method the CO2 is directly introduced into the water, it does increase the amount of carbon in the ocean more dramatically than any of the other methods.
Another approach analyzed is onshore geological storage, where emissions are injected into geological formations deep underground.  With this approach, there is a possibility of CO2 leaking from the geological container and being introduced to the atmosphere.  Therefore, this method was analyzed using three different leakage scenarios; rapidly, moderately, and weakly leaking projections.  The rapidly leaking geological formation scenario had effects similar to the deep-ocean and the ocean sediment methods with severe affects on all the measured factors, but the effects where delayed when compared to current practices.  The moderately leaking scenario was about half as severe as the rapidly leaking scenario and the peak was delayed by about 5,000 years after the ‘business-as-usual.’   The slowly leaking scenario had very little effect at all and was similar to the ‘best-case’ scenario, at least 50,000 years out when it was starting to show the same trends as the other scenarios, with rising effects in ocean carbon inventory and atmospheric and ocean warming.  This is to be expected because the slow leakage would cause a more drawn out and subtle effect on the factors being examined, but an effect none the less.
The last method analyzed is to inject CO2 into deep offshore ocean sediments.  This projection was done assuming that the sequestered carbon would ‘rapidly’ leak from the rock confines.  Since this is an offshore injection site, it will leak into the deep ocean layers.  Thus, the projections are similar to those of deep ocean sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–>, but delayed 1,000 years by the CO2 leaking out of the rock.

Shaffer concludes that while all these methods seem to minimize the effects of CO2 emissions, the long-term effects are still present.  He suggest that the best solution is to stop new emissions as soon as possible instead of trying to hide them away, and have them come back to cause trouble for future generations.

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