In many parts of the world, ethanol, produced by fermentation of carbohydrates from crops such as maize, sugar cane and sugar beet, is seen as way of supporting farmers and reducing dependence on imported fossil fuel. Higher oil prices are making “gasohol” increasingly economic, even without subsidies. Brazil's production from sugar cane is growing rapidly and they may soon become a major exporter1. Gasohol is presented as green petrol; the concept is superficially attractive - carbon is recycled from sugar cane to car to atmosphere and back to cane - but just how environmentally beneficial is it? A hectare of cane in Brazil can produce around 4 tonnes of ethanol, equivalent to around 5,000 litres of fossil fuel. After taking into account the fossil carbon needed to make the ethanol, there is around 13 tonnes of carbon dioxide (CO2) less released from fossil carbon for every hectare of land converted to sugar cane2. For biodiesel from soya oil the CO2 benefit is somewhat less.
On the other side of the equation is the cost in terms of creating agricultural land or the opportunity cost of not regenerating forest. When a hectare of forest is burnt and ploughed up, as much as 500 tonnes of carbon dioxide can be released into the atmosphere3. The damaging impact of this on atmospheric CO2 and global warming is immediate; even it it were recoverable, it would take nearly a century to overcome through the use of gasohol.
Regenerating rainforest on existing agricultural land takes some 20 tonnes of carbon dioxide/hectare out of the atmosphere each year as it grows; it is thus almost twice as efficient a strategy for reducing CO2 levels as making gasohol.
Whilst there may be short-term economic arguments for biofuels like gasohol and biodiesel, let us not be taken in by the green-wash. For climate change and for biodiversity they are a disaster. The logic of carbon taxation would demand they be taxed more highly than fossil energy, not less!
- Economist, 14 May 2005, 75-77. Special Report on Biofuels.
- Macedo, Copersucar Technological Centre
Greenhouse Gas Emissions and Avoided Emissions in the Production and Utilization of Sugar Cane, Sugar and Ethanol in Brazil: 1990-1994
www.mct.gov.br/clima/ingles/comunic_old/coperal.htm - Palm et al. 1999. Strategic information on changes in carbon stocks and land use.
www.asb.cgiar.org/data/dataset/IDAOJYZB.htm
This is an update on Prof. Righelato's previous post: How green is green diesel? from June 12, 2003
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Interesting stuff, not because of the content but
ReplyDeletebecause of the politics behind it. The content is interesting, and certainly the actual
carbon gains from bioethanol can be a suspect depending on the
system from which it is produced. One of the ways in which bioethanol
production makes any environmental sense is when it uses the wastes
from the existing sugar industry (molasses from the sugar refining process
and bagasse, the agricultural residue which is used to fuel the
distillation process). As for biodiesel from soya, soya oil is
essentially a waste product from extracting the protein from the bean
(the primiary reason for growing the crop, and a far more ecologically
sensible way of producing protein than beef, say), so convertion to
biodiesel is a way of adding value to the crop which also happens to
displace petroleum that would otherwise be burnt.
But in fact the logic in the article seems a bit muddled to me. One
assumption is that forests will grow where these crops are planted,
which is not always true, although perhaps he had Brazil in mind when
he wrote the piece and that was edited out. The other assumption is
that the world somehow does not demand these products (sugar, soya and
vegetable oil) and replanting forest would not displace some
wilderness value elsewhere in the world's agricultural landscape.
Besides, is forest regeneration is a realistic option, given all that
determines one particular course of action over another in modern
society. Its an idealistic option, for sure; everyone would like to see more forest
but without the economic arguement to make it happen it won't be
realised.
As with any criticism, it is no good shooting down an
option without offering a better alternative that
addresses the problem at hand, in this case liquid fuels for
transport. What are the alternatives? Often the hydrogen cell is
offered as the way forward, but realistically cars driven on H cells
are at least 10-20 years away so what are we going to do until then? H
cells have their own problems, too, that are waiting for technology to
solve - and where will the primary energy come from that will split
water to generate H2 and O2?
In my opinion, biofuels will only ever be a 'petroleum extender', allowing us to continue using our
diminishing petroleum resource more efficiently (since one gallon
will only contain 75% or 50% petroleum) while we get the long term
alternative operational.
Growing forests to sequester carbon is a pretty good option to remove
CO2 from the atmosphere, I agree, but unfortunately that is not the only issue at stake.
I think we need to grow more forests, but not at the expense of some of the few carbon reducing
options we have available.
We MUST make sure that we present the whole picture when we try and colour the opinions of others, and when it comes to the environmental health of the planet I cannot think of a more important cause to ensure we present all the facts accurately and leave politics out of it. Eh, Bush?
Anonymous makes some good points. Waste products such as molasses and spent edible oils are often cited as potential sources of biofuels; they can and should make a contribution (provided they do not displace demand to new agricultural production), but the quantities practically available are trivial compared with the scale needed for even a 1% contribution to petrol or diesel. Soya oil could make a much larger contribution but, at around 30% of the value from milled soybeans, it should not considered a waste product; demand for the oil is an important factor driving increased planting of the crop (the dominant product is, of course, the soya meal, most of which is used to feed cattle and poultry, not people directly - an environmentally destructive way of us getting our protein).
ReplyDeleteThe technology for making some biofuels is efficient, particularly for sugar cane: in making bioethanol from sugar cane in Brazil the bagasse provides the fuel for the mill and distillery and there is little waste. Despite this, the emissions saving from using the ethanol to substitute petroleum is less than would be obtained from letting the same land go back to forest; still less for sugar beet and the oil crops.
But the most important point is that for biofuels to make a significant contribution to transport fuels, huge quantities of cane, beet, maize, soya or oilseed rape are needed. For example, the current global area of sugar cane (about 20 million hectares) would need to be more than doubled for bioethanol from cane juice to give just a 5% substitution of global emissions from fossil fuels used in transportation. Pro rata, biofuels from other sources would use even more land. So, huge areas of land would have to be converted to production of the extra crops needed with attendant massive releases of carbon; or land would be kept in agricultural production that could otherwise be returned to forest (which applies to almost all of the tropics and much of the temperate zones).
Of course carbon emissions are not the only thing that will determine how land is used; social issues, economics and political expediency will bear on what is done and when. But our thinking should not be circumscribed by current land use patterns. In almost all situations, more carbon is held on the ground in the pre-agricultural forest or grassland state than in crop production. Converting to arable land releases most of the carbon, converting back to forest or grassland claws carbon dioxide back, slowly, but generally faster than can be achieved by the substitution of fossil energy by biofuels.
Renton Righelato
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