Last week The Economist published a detailed assessment of the state of play for capturing and storing the carbon dioxide emitted by power plants and factories. Although it skirted the assertion of many environmentalists that "clean coal" is inherently an oxymoron, the article's tone was generally skeptical concerning the cost and ultimate efficacy of the technology. Coincidentally, Greenpeace released a study featuring an ultra-low-carbon scenario created in conjunction with the European Renewable Energy Council. It proposes that by 2050 the US could shed all coal-fired power generation, as well as all nuclear power and most natural gas-fired power, along with nearly 80% of the petroleum used in transportation--all replaced by renewable electricity and biofuels. If the Economist regards carbon capture and sequestration (CCS) as "expensive and unproven", I can only imagine the terms it might use to describe the extraordinary transformation required to achieve the outcome Greenpeace envisions. The necessity of reducing greenhouse gas emissions dramatically by mid-century and the serious obstacles to replacing our entire energy economy with renewable energy sources in that time frame reinforce the importance of continuing to pursue CCS, in spite of its uncertainties.
I've been following CCS for a long time, and I've written about it many times on this blog. Without diminishing the technical challenges involved, I see them as being manageable with existing and foreseeable engineering know-how, without a scientific breakthrough. I attribute the prolonged absence of a large-scale demonstration of fully-integrated CCS on energy sources more carbon-intensive than natural gas to the mismatch between its costs and current monetary benefits. Whether the cost proves to be closer to the low or high end of the range of estimates included in the article, from roughly $40-115 per ton of captured CO2, it's hard to imagine a utility or oil company taking on the investment and operating expenses involved without the incentive of a transparent and fairly predictable price on carbon emissions. Whatever the cost of CCS might be, it can't be considered in a vacuum, and that is the biggest shortcoming of the Economist's otherwise thorough analysis.
As the US Congress prepares to embark on its latest effort to enact a greenhouse gas cap and trade bill, it's important to think about where its enormous pool of emissions savings will be found, and at what cost. CCS is only one option among many. Happily, a fair amount of work has been done in this regard, including a study by McKinsey & Co. for the Conference Board a little more than a year ago. A key chart from their report portrays a potential medium-term supply curve for emissions reductions. It indicates that while there might be a number of ways to cut CO2 at low or even negative cost--changes that would pay for themselves--achieving deeper cuts would require the contribution of costlier solutions, including CCS.
It's also worth noting that the current cost per ton of CO2 reductions from some of our current climate change strategies exceeds most estimates for CCS. In my recent posting on the application of energy storage to solar power, I calculated an effective cost of power for a couple of utility-scale solar projects in Florida at around $0.25/kWh. That's a premium of at least $0.20/kWh compared to a coal-fired power plant (without sequestration.) Based on typical emissions of 2.1 lb. of CO2 per kWh generated from coal, that implies an abatement cost of $190/ton of avoided CO2. In the likelier event that the power backed out by solar was generated from natural gas, the effective abatement cost could be even higher, because of the smaller emissions savings involved, despite the higher cost of gas-fired power compared to coal.
That comparison doesn't imply that solar power will always be a high-cost source of emissions reductions, or that CCS represents some kind of silver bullet for climate change. At the same time, coal now accounts for 23% of US primary energy consumption, 49% of our electricity generation, and nearly two-thirds of our baseload-capable generation. The difficulty of replacing baseload power with cyclical or intermittent sources makes me very skeptical of any low-emissions scenario that ignores CCS or assumes we can jettison coal entirely, not to mention forgoing nuclear power, the second-largest baseload power source in the US and by far our largest source of low-CO2 power. My specific comments on the Greenpeace scenario are posted elsewhere. At a minimum, any claims that it proves we can achieve the administration's 2050 emissions goals with only "green" energy options and efficiency gains are unwarranted. As useful as they are, scenarios can only point the way to possible futures. They can't provide firm proof of anything.
That leaves us with the hard work of cobbling together a broad set of climate solutions, in response to a price signal on emissions. In my assessment, that mix is very likely to include awkward elements such as CCS, along with deeply unglamorous things like improved farming and ranching practices. Contrary to the conclusions of the editorial accompanying the article on CCS, the technology is worth pursuing for reasons that have nothing to do with "placating the coal lobby." Nor does the cost of proving its feasibility look so high as to "deprive potentially cheaper methods of cutting emissions of cash and attention," particularly when the administration expects to carve out $120 billion for energy R&D from the proceeds of cap & trade over the next ten years. And even if it did, it's one of the few options that could be applied to reduce directly the emissions from the fossil fuels that still account for 85% of the energy we consume. That could make the difference between a manageable transition to a low-emissions world and an upheaval as bad as the current financial crisis.
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