We may never live it down. The sight of George W. Bush traipsing about his ranch in Texas, extolling the virtues of switchgrass-derived ethanol as a replacement for gasoline generated more than a few chuckles among scientifically literate environmentalists. Yet another example of the commander in chief’s fanciful world view, right? Probably. But a new study just published in the Proceedings of the National Academy of Sciences suggests that maybe, just maybe, he was on to something real.
“Net energy of cellulosic ethanol from switchgrass” by M.R. Schmer, et al. at the University of Nebraska concludes that if burning bioethanol produced from switchgrass, a woody perennial that goes by the Latin name Panicum virgatum and grows with little help from farmers, could cut our greenhouse gas emissions dramatically.
From the abstract:
Switchgrass produced 540% more renewable than nonrenewable energy consumed. Switchgrass monocultures managed for high yield produced 93% more biomass yield and an equivalent estimated NEY [net energy yield] than previous estimates from human-made prairies that received low agricultural inputs. Estimated average greenhouse gas (GHG) emissions from cellulosic ethanol derived from switchgrass were 94% lower than estimated GHG from gasoline.
A 94 percent cut! Whoo hoo!
But that’s not all. As the study was based on seedstocks and techniques available six and seven years ago, and assuming that “green revolution” improvements can be applied to switchgrass, there’s no reason to believe that the net energy yield wouldn’t be even bigger;
As an indicator of the improvement potential, switchgrass biomass yields in recent yield trials in Nebraska, South Dakota, and North Dakota (36-38) were 50% greater than achieved in this study.
There must be a catch.
Well, yes. The study involved involved tiny test plots, not large-scale farms and conversion facilities to turn all that cellulose into ethanol. There are no dollar figures attached. Plus,Nature magazine’s coverage included this not-insignificant caveat:
Rainer Zah, head of the Life Cycle Assessment & Modelling group of the Swiss Materials Science and Technology research institution, EMPA, in Saint Gallen, is more concerned about another greenhouse gas, namely dinitrogen oxide, which is much more potent than carbon dioxide. If this gas is not properly modelled, the greenhouse benefits of switchgrass could be wildly overestimated, he says.
Zah agrees that switchgrass holds promise as a fuel, but notes that there is some way to go before the energy yield estimated by Vogel can be realized.
Switchgrass locks its carbon in as woody lignin and cellulose, which needs to be broken down to sugar and starch before it can be used as a fuel. The facilities needed to do this currently exist only on small scales for pilot projects. “The technology to make full use of all the carbon in switchgrass is not yet established,” says Zah.
And as one commenter noted at the Nature story page, converting wild prairie to switchgrass fields isn’t exactly what the existing wildlife need. “There is no alternate Earth where we can leave the switchgrass to function as part of a healthy ecosystem. We can’t have it both ways on the same plot of land,” wrote “Jean SmilingCoyote.”
I hate the idea of choosing between wilderness and climate change mitigation. But sometimes you have to choose the lesser evil, which in this case would be wrecking some prairie ecosystems in favor of a fuel to replace gasoline. It’s not the only answer, of course. We’re still going to need to stop driving so much, reintroduce serious passenger rail and so forth. But we’re still going to need considerable quantities of fuel to move us and our things around. At the very least, this study lends supports to the campaign to pour lots and lots of money into further research on renewable fuel supplies.
Remember that corn-derived ethanol might (if you are lucky) save you a mere 25 percent, and that much of the biodiesel on the market comes from ecosystem-ravaging palm plantations. Fred Pearce and Peter Aldhous wrote in New Scientist a couple of weeks back that
…a slew of new studies question the logic behind expanding biofuel production. For a start, there may not be enough land to grow the crops on or water to irrigate them, given other demands on global agriculture. Worse, any cuts in carbon dioxide emissions gained by burning less fossil fuels may be wiped out by increased emissions of the greenhouse gas nitrous oxide from fertilisers used on biofuel crops.
According to Johan Rockström, executive director of the Stockholm Environment Institute in Sweden, switching 50 per cent of the fossil fuels that will be devoted to electricity generation and transport by 2050 to biofuels would use between 4000 and 12,000 extra cubic kilometres of water per year. To put that in perspective, the total annual flow down the world’s rivers is about 14,000 km3.
A more modest target of quadrupling world biofuel production to 140 billion litres a year by 2030 – enough to replace 7.5 per cent of current gasoline use, would require an extra 180 km3 of water to be extracted from rivers and underground reserves, calculates Charlotte de Fraiture at the International Water Management Institute, based near Columbo in Sri Lanka.
By comparison, switchgrass is looking pretty good. Let’s spend what it takes to bring this stuff to market. I’ll live with the inconvenient truth that Bush was just ahead of the curve. For once.