Noneconomic considerations

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The work presented here has focused on estimating the comparative costs of various methods of producing and delivering carbon neutral transportation fuels. There are, of course, external factors such as food production and geopolitical realities, which will exert market pressures on the chosen method of fuel production. Some efforts have been made to quantify the effects of biofuel production on food prices (Walsh et al. 2003) and the effects of a global change to a Western, meat-based diet

Geoengineering Air Capture
Figure 7.6 Effect of reduced cost of hydrogen distribution, as measured by market penetration, on the allowable cost of air capture.

(Hoogwijk et al. 2003). These effects are difficult to quantify and also depend on the pathway. Projections to 2050 and beyond may reflect gradual changes but annual changes, such as switching crops, may have a dramatic impact on food prices. We will not delve into the food debate beyond raising the question of who gets to decide when it is time to grow food or fuel.

A carbon neutral fuel is of little use unless consumers purchase vehicles designed to use those fuels. Currently, the consumer and commercial vehicle fleet is dominated by hydrocarbon-based internal combustion engines. The large volume of vehicle sales, 20 million annually in the USA, has led to economies of scale in production that make introducing a new vehicle type more expensive. Some hydrogen vehicles are available but the cost is two orders of magnitude higher than conventional vehicles (Mayersohn 2007). Additionally, electric vehicles are at least one order of magnitude more expensive than gasoline-powered cars (Tesla Motors 2008, http://www.teslamotors.com/buy/buyPage1.php). While electric vehicles require a different infrastructure, the expected price of electricity with CCS, which ranges from $0.05 to $0.07 (kW h)-1 ($14-20 GJ-1; IPCC 2005), can be compared with the fuel costs in Figure 7.2. Additionally, the consumer has come to expect certain attributes in a vehicle, including range and interior space, which may drive up the effective cost of alternative technologies. The premium afforded to hydrocarbon fuels may be quite substantial (Keith & Farrell 2003).

Land-use change is also an important consideration for carbon neutral transportation fuels. Recent work has highlighted the importance of considering emissions over the complete life cycle of the fuel production process including indirect emissions from land-use change as a result of biofuel production. Once included, the life-cycle emissions of food-based biofuels change from slight reductions (20 per cent) to net emitters for at least 40 years (Fargione et al. 2008; Searchinger et al. 2008). Only cellulosic fuels from abandoned or degraded cropland do not result in an immediate release of carbon stores, although the potential carbon accrued through reforestation is not included. Cellulosic fuels were found to be the most economical in this work but their net greenhouse gas reductions must be subject to the same analysis as food-based fuels. Specifically, the carbon accounting must include roots and soil carbon as well as detritus from harvesting. Fargione et al. (2008) suggested that slash and thinning from sustainable forestry along with the use of carbonaceous wastes may provide the lowest net emissions. By contrast, CNHCs based on air capture, as well as hydrogen and electricity, are not dependent on the biosphere. They have the benefit of simple accounting with readily verifiable emission profiles as opposed to indirect emissions from biofuels, which may span the globe.

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