Tuesday, January 8, 2008

[PBN] Scientific Limits to Biofuels

Source: New Scientist

1. Is the biofuel dream over?

* 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.

The misgivings come as delegates from around the world gather in Bali,
Indonesia, this week, to begin work on a tougher climate agreement to
succeed the Kyoto protocol.

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.

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

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.


* Johan Rockström's study on water use

* Charlotte de Fraiture's study of water use

* Sten Nilsson's global map study

* Paul Crutzen's study on nitrous oxide emissions

From issue 2634 of New Scientist magazine, 15 December 2007, page 6-7

Check for earlier Pacific Biofuel posts: http://pacbiofuel.blogspot.com/

No comments: