Wednesday, January 31, 2007

The best method of carbon sequestration

Now that the Bush administration has admitted something every thinking person already knows--that the world is warming--and now that the administration is fully behind the search for alternative fuels, we can expect more talk about the benefits of carbon sequestration.

For some people carbon sequestration offers the best of all possible futures. Presumably, we could continue to burn plentiful coal supplies long after oil and natural gas production declines. With the proper technology we could then capture the resulting carbon dioxide (the main greenhouse gas) before is it released into the atmosphere. This would supposedly give us the necessary breathing room to make a gradual transition to a renewable energy economy with a minimum of disruption.

The initial schemes for sequestering carbon such as placing it in caverns underground sound easy enough. But several concerns arise. Can leaks be avoided, not just immediately, but over a period that might last many thousands of years? Will the carbon dioxide react with the surfaces of the cavern opening up pathways to the air above? Such reactions have been noted, but whether they would ultimately result in substantial leaks remains unknown. Can all the existing drill holes into such a cavern be found, adequately sealed and monitored for an indefinite period of time? In other words, who will be babysitting these sites 100, 200, even 500 years from now?

One sequestration scheme already in use stores carbon dioxide in an aging oil field. The injected CO2 is used to force out the remaining hard-to-get oil. As clever as this seems, it's worth asking whether any net reduction in greenhouse gasses occurs since the recovered oil is ultimately burned.

Yet another land-based method involves injecting carbon dioxide into underground saline aquifers which will presumably never be used for human consumption. The supposed advantage of this method is that saline aquifers are widespread whereas suitable caverns and old oil fields are not nearly as widely or conveniently located. No one really knows whether this would result in permanent storage or whether the drill holes used to reach the aquifers or other holes intentionally or inadvertently drilled in the past or the future can be adequately monitored. Even the extent of an aquifer and its communication with other aquifers and with the surface are difficult to ascertain.

Another often touted method is to use the mineral serpentinite which will combine with CO2 from power plant flues to form a stable magnesium compound. Energy costs and storage problems could be substantial. And, while serpentinite is relatively abundant, it's not clear whether there would be enough of it with sufficient concentrations of magnesium to handle the projected need.

The open sea apparently offers even greater possibilities including pumping carbon dioxide to the bottom of the ocean. At great depths the pressure and low temperature would maintain the CO2 in liquid form which is heavier than water. Presumably the liquid carbon dioxide would simply hang out for millennia. The financial and energy costs of gathering and transporting the CO2, perhaps in liquid form using an elaborate pipeline system, seems to be the major hurdle. In addition, what we know about the bottom of the oceans is probably less than what we know about the nearest star. Can we really be sure that the CO2 will stay where we put it?

As I said above, all of this effort is focused on allowing us to use coal for the foreseeable future. The coal infrastructure is already in place, and it works to produce more than half the electricity in the United States. What is not considered is the use of coal to make liquid fuels which would replace those now provided by oil. Coal-to-liquids, as it is called, is a very carbon intensive process. Even if the carbon emitted from the coal-to-liquids refineries were captured and sequestered, there is currently no practical way to capture and sequester carbon from a moving vehicle. This is no small matter. In the United States vehicles create 27 percent of all greenhouse gas emissions.

Given the uncertainties, the costs and the alternatives available to us--conservation, efficiency, wind and solar--does it make sense to build a hugely expensive sequestration infrastructure that will essentially be a giant subsidy for the coal industry? Can we even be sure that exponentially increasing rates of coal production could be sustained? In other words, would we not be bringing forward a peak in coal production, perhaps by the middle of this century and then face all the same questions about a transition to a non-fossil fuel economy? Finally, given that we cannot guarantee the successful long-term sequestration of CO2, would it be moral to commit future generations to such a risky path?

When you think all this through, there is one method of carbon sequestration that stands head and shoulders above the rest. Leave the carbon in the ground to the greatest extent possible and get on with the project of creating a genuinely sustainable society.


Anonymous said...

You hit it in one!. The coal industry has been on notice of the need to address sequestration for at least 15 years and chosen to do little about it. The current R&D investment is minimal, results are uncertain and far into the future - too little too late.
There should be no further approval for major coal projects until the carbon can be fully sequestered - should be a reasonable spur to innovation!

Anonymous said...


A while back Brad Allenby reported ( on technologies that are able to remove CO2 from ambient air, creating various carbon-based materials in the process. I'd be interested to know if you believe this is a feasible approach to sequestration?


Kurt Cobb said...


I have no doubt that carbon capture from the air or large mirrors in space or even sulfate aerosols are technically possible. They will undoubtedly turn out to be very expensive and those proposing them clearly believe that energy supplies will not be constrained for the forseeable future. Still it's hard to see how energy from carbon-based fuels which currently provide 86 percent our energy could be used to take carbon out of the air without essentially running in place. If they are used this way, then how much energy will be left over to power society. That aside, the most important maxim about fiddling with the environment is that you can never do just one thing. To pretend that we know exactly what the consequences of putting mirrors in space or sulfate aerosols in the skies will be is naive to the utmost. There will certainly be unexpected feedbacks and causation loops that we know nothing about now. The potential to unknowingly affect weather patterns seems enormous. To rely on such schemes instead of reducing our carbon output seems wildly risky. To assume that we could simply adjust the carbon dioxide level to our liking as Allenby suggests shows that he knows little about natural systems and how they work.

Anonymous said...

Excellent comment. I would nominate planting trees as the most environmentally sound method of carbon sequestration. Through renewable solar energy chemistry, without the need to convert the photons to electricity, CO gas is cracked by plants into elemental carbon (which is retained) and oxygen gas (which is liberated into the environment). This is cheap, requires no fossil fuel inputs, and is self-regulating and self-replicating. I don't think we can plant enough trees, or plant them fast enough, to catch up to carbon dioxide production. Unfortunately, Gaia is infected with a very selfish and uncontrolled virus - Homo sapiens -- which is consuming space on the surface of the planet through "development." Plants are being exterminated and crowded out, sometimes burned just to clear land for agriculture and building. Ironic: There was a Scientific American article several years ago which argued that the first energy crisis in England and Europe occurred when the available trees had all been used up for fuel, and people were forced to turn to mining peat and coal for heat and light. The world is not yet all used up in the 21st century, but our governments don't have the will to stop "development" because the developers, who need stable markets, security, and economic predictability, are the biggest supporters of status quo government.

Anonymous said...

Hello Kurt,

just dropping a message to say hello. Slowly but surely, I am on the way of accumulating posts of yours translated...

This last one is done.

According to website statistics, your section is quite a success.


Brian said...


I reposted something from The Oil Drum re injecting CO2 in oil fields:

The CO2 from the extra oil exceeds the amount of CO2 put in.

Important subject, though.