If we are going to avoid catastrophic climate outcomes, we need some 11 “stabilization wedges” from 2015 to 2040 (see here). So if you want to be a core climate solution, you need to be able to generate a large fraction of a wedge in a climate-constrained world. And that is a staggering amount of low-carbon energy (see “Is 450 ppm politically possible? Part 1“).
Princeton’s Socolow and Pacala describe one wedge of biofuel in their original August 2004 Science article on the wedges:
Option 13: Biofuels. Fossil-carbon fuels can also be replaced by biofuels such as ethanol. A wedge of biofuel would be achieved by the production of about 34 million barrels per day of ethanol in 2054 that could displace gasoline, provided the ethanol itself were fossil-carbon free. This ethanol production rate would be about 50 times larger than today’s global production rate [actually, now more like 60 times current U.S. biofuels production], almost all of which can be attributed to Brazilian sugarcane and United States corn. An ethanol wedge would require 250 million hectares committed to high-yield (15 dry tons/hectare) plantations by 2054, an area equal to about one-sixth of the world’s cropland. An even larger area would be required to the extent that the biofuels require fossil-carbon inputs. Because land suitable for annually harvested biofuels crops is also often suitable for conventional agriculture, biofuels production could compromise agricultural productivity.
Biofuels thus have several problems as a large-scale medium-term climate solution:
First, virtually all crop-based biofuels are worthless from a climate perspective (see “About those two studies dissing biofuels“) and probably a bad idea from most other perspectives (see “Let them eat biofuels!“). Second, there is not a single commercial cellulosic ethanol plant in United States yet. Third, I’m not sure there is an agreement in the scientific community about how to do lifecycle analysis needed to determine the net carbon benefit from cellulosic fuels.
Fourth, in a post-2050 world with 3 billion more people who are losing water from melting glaciers and desertification, arable land and water will be very dear commodities. That means the only biofuels that would make sense to fight global warming would be ones that do not require arable land or much fresh water.
So I think the jury is very much out on whether a wedge-scale contribution from cellulosic biofuels is practical and affordable and a climate-constrained world. It should probably be considered a half-wedge solution until we see major advances in large-scale microalgae-to-biofuels.
If you want to see the entire Princeton discussion on the biofuels wedge with all of their assumptions detailed, go here.
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