Fossil Fuels & CO2 Sequestration: Benefits and Risks
Dr. Christopher James Backhouse
Professor, Department of Electrical and Computer Engineering,
University of Alberta
Email: 
31 August 2008
Abstract
I have read of some concerns regarding the long term effects of dealing with our planetary excess of CO2 by taking it out of circulation, i.e. sequestering it. The worrisome issue is that for every C there are two Os. At least at the time I first started thinking about it there was no estimate of how good an idea this may be. Existing risk assessments (e.g. ref) seem to deal only with containment issues. Incomplete assessments are likely to lead to poor decisions while undermining public confidence in the decision-making (and regulatory) process. This note is meant to be a starting point, an initial assessment of the 'pros and cons' associated with the loss of the carbon and oxygen from our atmosphere.
A simple (i.e. 'ballpark') calculation with:
The Earth taken to be a sphere of radius ~6,400 km (ref) and hence an area of 4πr2/3
A very crude approximation of our atmosphere as having room temperature and a pressure of 1 atm up to an altitude of 10 km (i.e. about the top of Everest...) and then vacuum.
1 mole of diatomic gas under the above conditions has a volume of 27 litres.
The atmosphere is about 20% oxygen
1000 lites per cubic metre
This gives an amount of atmospheric oxygen (i.e. O2) of 10 19 moles.
A simple calculation with:
Gives 2 x 1015 moles of carbon for each barrel, or 2 x 1012 moles of carbon per day.
Assuming that CO2 production stays constant, this gives us 5 x 106 days, or about 15,000 years.
If global CO2 production drops to zero within the next century as we switch to clean and renewable energy, then the long term impact could be negligible.
Global CO2 production has increased by a factor of 10 since 1950, a continuation of such dramatic growth could substantially shorten the above timeline (ref). If the whole world consumed energy at the same rate as the present-day U.S. (or Canada), with complete sequestration, then from the above sources we would expect to see a further increase of 20x, corresponding to about 750 years before we have nothing to breathe!
As a stopgap measure this may work... However:
Let's hope that we keep track of time and do not come to think of 5% oxygen levels as being normal! (This phenomenon of not noticing slow change is commonly referred to as "Creeping Normalcy")
An estimate of the time needed to cycle all atmospheric oxygen through the photosynthesis process is 2000 years. (ref) This suggests that the present capability of the ecosystem to regenerate O2 from CO2 is about 7 times larger than our present CO2 production. Not surprisingly then, there appears (so far) to be "little impact" on the amount of oxygen in the atmosphere (ref). However, if our CO2 production continues to grow then we could easily exceed that regeneration rate. In addition, if the ability of the ecosystem to regerate that oxygen is impaired (e.g. less forest) the regeneration rate could become significantly lower. If either happens then:
If we sequester, we would have a steadily decreasing amount of free oxygen in the atmosphere. We may see a change in the planetary biomass as some forms of life (i.e. anaerobic bacteria) that were once dominant (billions of years ago) start to play a larger role. These might have a very large environmental impact since the bacterial biomass vastly exceeds our own.
If we do not sequester, then we would likely start seeing a steadily increasing level of CO2, and a (slower) decrease in O2. Apart from the impact on the greenhouse effect, there could be significant effects on a wide range of phenomena, from the weathering of rock, to the level of human alertness (ref).
There is a lot of interesting research into the role that (for instance) soils, reefs, plants and geology play in maintaining an atmospheric balance. Somehow the above mechanisms have achieved some sort of equilibrium, and the planet has been aerobic (i.e. atmospheric oxygen present) for billions of years. The permanent sequestering of materials might change this.
Humanity is now facing a severe challenge - a race to develop more sustainable energy sources before we run out of fossil fuels. The stakes are very high since we depend on energy in order to have enough food. In this context, it seems inevitable that the oil-sands will play a major role in oil production in the next decades - a critical period for humanity. However, concern (and political pressures) have recently been rising regarding the amount of carbon released by the recovery of oil from the oil-sands, leading to charges that the oil is 'dirty'. This document was written in Alberta, Canada - a major oil-sands region. The response of the industry and government here has been to emphasize sequestration as a strategy. This document is meant to provide some caveats:
If the sequestration is part of an effective long-term strategy then it could be an effective tool, one that is well-received by the world community. This would mean that the sequestration would have to be a short-term stopgap measure that controls the greenhouse effects of excess CO2 levels without meaningfully changing the aerobic status of our planet. To be effective and credible such a strategy would have to support the efforts of the planet to right the CO2 vs O2 balance (effective environmental stewardship), and the efforts of the research community and industry to move us to more sustainable energy production.
If the sequestration is not seen as being part of an effective long-term strategy, or one that could lead to significant changes in the CO2 and O2 levels, then it would be a public-relations disaster for the region and the industry. To date there has been a moderate amount of pressure on Albertan industry and government due to the contribution of the oil-sands recovery process to global warming. Imagine the amount of pressure if industry and government were instead seen as removing the air we breathe.
This is an issue of interest for me although not one that I have any particular expertise in. Although I am typically swamped with teaching, paperwork and research, I would like to hear of any errors or suggestions. If you have any, then please email me as above, with the subject line of 'ATTN CO2'. Depending on time, I may not be able to reply - but thank you in advance.