- 15 December 2007
- From New Scientist Print Edition.
- Fred Pearce
- Peter Aldhous
Can biofuels help save our planet from a climate catastrophe? Farmers and fuel companies certainly seem to think so, but fresh doubts have arisen about the wisdom of jumping wholesale onto the biofuels bandwagon…….
About 12 million hectares, or around 1 per cent of the world’s fields, are currently devoted to growing biofuels. Sugar cane and maize, for example, are turned into bioethanol, a substitute for gasoline, while rapeseed and palm oil are made into biodiesel. That figure will grow because oil is so costly, and because biofuels supposedly emit fewer greenhouse gases than fossil fuels.
But 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.
In parts of the world, shortage of water is already putting a brake on agricultural productivity. 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.
That target may be manageable across much of the globe. But in China and India, where water is in short supply and most crops require artificial irrigation, de Fraiture argues that there is not enough water even to meet existing government plans to expand biofuel production.
Another contentious issue is how much land is available to grow biofuels (New Scientist, 25 September 2006, p 36). And the answer appears to be not much, a point that Sten Nilsson, deputy director of the International Institute for Applied Systems Analysis in Laxenburg, Austria, makes using a “cartographic strip-tease” based on a new global mapping study.
Beginning with a world map showing land not yet built upon or cultivated, Nilsson progressively strips forests, deserts and other non-vegetated areas, mountains, protected areas, land with an unsuitable climate, and pastures needed for grazing (see Maps). That leaves just 250 to 300 million hectares for growing biofuels, an area about the size of Argentina.
Even using a future generation of biofuel crops – woody plants with large amounts of cellulose that enable more biomass to be converted to fuel – Nilsson calculates that it will take 290 million hectares to meet a tenth of the world’s projected energy demands in 2030. But another 200 million hectares will be needed by then to feed an extra 2 to 3 billion people, with a further 25 million hectares absorbed by expanding timber and pulp industries.
So if biofuels expand as much as Nilsson anticipates, there will be no choice but to impinge upon land needed for growing food, or to destroy forests and other pristine areas like peat bogs. That would release carbon now stashed away in forests and peat soils (New Scientist, 1 December, p 50), turning biofuels into a major contributor to global warming
De Fraiture is more optimistic. Her modest projection for a quadrupling of biofuel production assumes that maize production will be boosted by 20 per cent, sugar cane by 25 per cent and oil crops for biodiesel by 80 per cent. Assuming future improvements in crop yields, de Fraiture estimates that this might be done on just 30 million hectares of land – or 2.5 times the area now under cultivation.
Even today’s biofuel yields depend on generous applications of nitrogen-containing fertiliser. That contributes to global warming, as some of the added nitrogen gets converted into nitrous oxide, which is a potent greenhouse gas. Over 100 years it creates 300 times the warming effect of CO2, molecule for molecule. And now researchers led by Paul Crutzen of the Max Planck Institute for Chemistry in Mainz, Germany, who won a share of a Nobel prize for his work on the destruction of the ozone layer, claim that we have underestimated these emissions. Factor in their revised figures, and cuts in CO2 emissions as a result of replacing fossil fuels may be wiped out altogether.
“Fertilisers contribute to global warming, as some of the added nitrogen gets converted into a potent greenhouse gas”
The Intergovernmental Panel on Climate Change suggests that between 1 and 2 per cent of nitrogen added to fields gets converted to nitrous oxide, based on direct measurements of emissions from fertilised soils. But nitrogen from fertiliser also gets into water and moves around the environment, continuing to emit nitrous oxide as it goes. To estimate these “indirect” emissions, Crutzen and his colleagues calculated how much nitrogen has built up in the atmosphere since pre-industrial times, and estimated how much of this could be attributed to the use of fertilisers.
This suggested that between 3 and 5 per cent of the nitrogen added to the soil in fertilisers ends up in the atmosphere as nitrous oxide. Crucially, that would be enough to negate cuts in CO2 emissions made by replacing fossil fuels. Biodiesel from rapeseed came off worse – the warming caused by nitrous oxide emissions being 1 to 1.7 times as much as the cooling caused by replacing fossil fuels. For maize bioethanol, the range was 0.9 to 1.5. Only bioethanol from sugar cane came out with a net cooling effect, its nitrous oxide emissions causing between 0.5 and 0.9 times as much warming as the cooling due to fossil fuel replacement.
These simple calculations, which set increased nitrous oxide emissions against reductions in CO2 emissions caused by replacing gasoline or diesel with biofuels, do not account for all the greenhouse gas emissions associated with producing, processing and distributing the various fuels. Now Michael Wang of the Argonne National Laboratory in Illinois has taken Crutzen’s upper estimate for nitrous oxide emissions and plugged it into a sophisticated computer model which does just that. When he did so, bioethanol from maize went from giving about a 20 per cent cut in greenhouse gas emissions, compared to gasoline, to providing no advantage at all. Still, Wang suspects that Crutzen’s method may overestimate nitrous oxide emissions. “It is a very interesting approach,” he says. “But there may be systematic biases.”
Crutzen stresses that his paper is still being revised in response to comments he has received since August, when a preliminary version appeared online. “Here and there the numbers may change. But the principle doesn’t,” he says. “It’s really telling us about a general problem with our lack of knowledge about the nitrogen cycle.”
With governments and businesses backing biofuels as part of a “green” future, that represents a disturbing gap in our knowledge.
From issue 2634 of New Scientist magazine, 15 December 2007, page 6-7
So the biofuel solution is running into problems, well its an emerging technology and it isn’t the only solution / possibility for humans to switch away from fossil fuels and other green house contributors.
Onwards, always onwards 🙂