Another study dissing biofuels

Biofuels can’t get any respect these days. Science magazine (subs. req’d) recently published an article whose abstract reads, simply,

The carbon sequestered by restoring forests is greater than the emissions avoided by the use of the liquid biofuels.

The article, “Carbon Mitigation by Biofuels or by Saving and Restoring Forests?” notes:

Two issues need to be addressed before the efficacy of biofuels can be assessed: the net reduction in fossil carbon emissions (avoided emissions) arising from use of agriculturally derived biofuels and the effect of alternative land-use strategies on carbon stores in the biosphere.

What happens when you do this analysis?

In all cases, forestation of an equivalent area of land would sequester two to nine times more carbon over a 30-year period than the emissions avoided by the use of the biofuel. Taking this opportunity cost into account, the emissions cost of liquid biofuels exceeds that of fossil fuels.

Does any source of biomass justify using land for biofuels? Yes:

[O]nly conversion of woody biomass may be compatible with retention of forest carbon stocks. Woody biomass can be used directly for fuel or converted to liquid fuels. Although still in a development stage, avoided emissions in temperate zones appear similar to assimilation by forest restoration. Moreover, it may be possible to avoid environmental problems associated with extensive monoculture by harvesting from standing forests. In this case, soil and above-ground carbon stocks may be built up in parallel with sustainable harvesting for fuel production.

So over the longer term, cellulosic ethanol may still turn out to be a good idea. Still, the authors have a clear conclusion:

If the prime object of policy on biofuels is mitigation of carbon dioxide-driven global warming, policy-makers may be better advised in the short term (30 years or so) to focus on increasing the efficiency of fossil fuel use, to conserve the existing forests and savannahs, and to restore natural forest and grassland habitats on cropland that is not needed for food. In addition to reducing net carbon dioxide flux to the atmosphere, conversion of large areas of land back to secondary forest provides other environmental services (such as prevention of desertification, provision of forest products, maintenance of biological diversity, and regional climate regulation), whereas conversion of large areas of land to biofuel crops may place additional strains on the environment. For the longer term, carbon-free transport fuel technologies are needed to replace fossil hydrocarbons.

3 Responses to Another study dissing biofuels

  1. John Mashey says:

    (I read your book – good stuff).

    A few questions:

    1) on p. 196, you note that if oil prices in 2020 are consistently higher than $70 a barrel, cellulosic ethanol could be a competitive alternative fuel.
    I see oil broke $90/barrel Friday, so maybe we’ll get there sooner.
    Maybe George Bush is owed thanks for causing Iraqi oil to stay in the ground a lot longer. :-)

    Q: a lot of people seem enthusiastic for miscanthus, and in tropics, jatropha for biodiesel. Any opinions on these?

    2) Any opinions on the Toyota 1/X concept car?

    3) Any opinion on the 2004 Ayres & Warr paper?

    4) Some of the anti-ethanol folks (not you) seem to think there is a strict tradeoff between growing food and growing fuel, saying that it would be terrible to grow fuel and have less corn to send to starving people. I see that moderately often.

    On the other hand, North American farming depends so heavily on cheap mechanization and transport to get food to people that it’s hard to understand the future of such agriculture without spending some of the acreage on fuel. When there’s no petroleum, finally, it’s hard to believe there will be a lot of mass shipping of bulky food halfway across the world.

    Assuming that people use electric tractors and such when possible, and that there is effectively no petroleum or natural gas left (and please, no massive synfuels), have you seen any good studies modeling what large-scale agriculture might look like? Say in 2100?

    I am assuming that we won’t have a mass movement to vastly increase the number of farmers and go back en masse to Old Amish style farming, but unless there is something for medium-to-long-distance food transport, it’s going to get tough for some big cities.

    Of course, less high-fructose corn syrup may not be such a bad idea.
    Likewise, it will be interesting to see the role of tobacco.

  2. Earl Killian says:

    To John Mashey:
    I think the most appropriate use of biofuels (e.g. algae biodiesel) will be as the backup liquid fuel for plug-in hybrids and for long-distance freight. Every time I have looked, electricity has always beaten biofuels by many multiples, so the only time biofuels make sense are when electricity won’t do the job. So algae biodiesel might be used for long-distance freight (electricity can handle short-distance fine) simply because truckers cannot reasonably plug-in on many of their routes.

    Why does electricity win over biofuels? Take a look at the most efficient biofuel that I know of, the aforementioned algae biodiesel (15,000 gallons per acre-year). Select algal species can convert sunlight into oil at 7.5% efficiency. Compare this with 30% efficiency for a solar thermal electric power plant, and you see you are starting with a 4x efficiency head start. Now consider that electric motors are 4x the efficiency of internal combustion engines, and now you’re looking at a 16x advantage (hybrids seem to be able to buy back some of this, so call it only 8x). So to replace petroleum in the U.S. with sunlight, you either need 6,000km^2 if you convert to electricity, or 48,000km^2 if you use algae biodiesel. (Another estimate of the land area to replace petroleum for algae biodiesel was 15,000mi^2, or 39,000km^2, which is close enough to the above for these purposes to serve as confirmation.) The 6,000km^2 seems much more reasonable to implement.
    For comparison, the Mojave desert is 57,000 km^2, the Sonoran desert is 311,000 km^2, and Iraq is 438,317 km^2. I suspect the desert southwest is also a little easier for the U.S. to defend than Iraq.

    Finally, if one is really interested in biofuels, despite the above, one should look at Tilman’s Carbon-Negative Low-Intensity High-Diversity Biomass paper last year. One can at least imagine such agriculture being less mechanism intensive than today’s agriculture (prairies being self-creating after all). Of course, reiterating my theme, Tilman therein estimated that (in the supplementary materials) that producing electricity was better than producing ethanol. So why use 2,000,000 mi^2 of prairie when 1,000,000 mi^2 will do?

  3. John Mashey says:

    Thanks, I’ll go look up Tilman.
    Yes, I think we mostly agree (i.e., that electricity generally wins, especially for local stuff.) are pretty cool, as are:

    My main concern is medium/long-distance transport, and some large farming uses. When I was growing up on a farm, there were a lot of dependencies on weather, but fuel wasn’t one of them. At least, rural electrification happened a long time ago, maybe if we get a good infrastructure for standardized modular battery-packs that will help.