Liquid Biofuels for Transport Prospects, risks and opportunities
4. What are the environmental impacts of biofuel production?
- 4.1 Can biofuels help mitigate climate change?
- 4.2 What changes to agricultural land would biofuel production require?
- 4.3 How will biofuel production affect water resources?
- 4.4 How will biofuel production affect soils?
- 4.5 How will biofuel production affect biodiversity?
- 4.6 How could an environmentally sustainable biofuel production be ensured?
4.1 Can biofuels help mitigate climate change?
To assess the net effect on greenhouse gas emissions of replacing fossil fuels by biofuels, we need to analyse emissions throughout the whole process of producing, transporting and using the fuel. Life-Cycle Analysis is the main tool used to do this. It compares a specific biofuel system with a reference system – in most cases petrol.
Greenhouse gas balances differ widely depending on the type of crop, on the location, and on how feedstock production and fuel processing are carried out. Biofuels from some sources can even generate more greenhouse gas emissions than fossil fuels.
A significant factor contributing to greenhouse gas emissions is the amount of fossil energy used for feedstock production and transport, including for fertilizer and pesticide manufacture, for cultivation and harvesting of the crops, and or in the biofuel production plant itself.
Emissions of nitrous oxide are another important factor. It is released when nitrogen fertilizers are used and its greenhouse gas effect is about 300 times stronger than that of carbon dioxide.
By-products from biofuel production such as proteins for animal feed make a positive contribution to climate change mitigation because they save energy and greenhouse gas emissions that would otherwise have been needed to produce the feed by other means.
Most studies have found that producing first generation biofuels usually yields reductions in greenhouse gas emissions of 20 to 60% when fossil fuels are replaced provided the most efficient systems are used and carbon dioxide emissions from changes in land-use are excluded.
Ethanol produced from sugar cane in Brazil and second-generation biofuels typically reduce emissions by 70 to 90%, again excluding carbon releases related to land-use change.
However, changes in land use can have dramatic effects on greenhouse gas emissions. When forest or grassland is converted to farmland to produce feedstocks, or to produce crops that have been displaced by feedstock production, carbon stored in the soil is released into the atmosphere. The effects can be so great that they negate the benefits of biofuels. Repaying this ‘carbon debt’ could take decades or even hundreds of years. In some cases it would be more cost-effective to strive for greater fuel efficiency and carbon sequestration through reforestation and forest conservation.
4.2 What changes to agricultural land would biofuel production require?
Since land-use changes have a significant impact on
greenhouse gas emissions,
it is important to know whether increased
biofuels production will be
met through improved land productivity or through expansion of
Expansion of cultivated land
Of the world’s 13.5 billion hectares of total land surface
area, about 8.3 billion hectares are currently grassland or
forest and 1.6 billion
hectares cropland. After excluding forest land, protected areas
and land needed for food, between 250 and 800 million hectares,
are potentially available for the expansion of
biofuel crop production.
In 2004, about 1% of global cropland was being used for
biofuels, and the IEA
expects this share to increase to 3 to 4 times this level by
2030. Some land that was not profitable in the past could be
returned to production, for example in the Former Soviet Union.
In practice, additional land is expected to come from non-cereal
croplands and set-aside land in Australia, Canada, the USA and
the EU, with some new, currently uncultivated land, especially
in Latin America and Africa.
Intensive research has produced significant improvements in
crop yields, but has focused on specific crops and regions. In
many parts of the world actual yields are still below their
potential. Africa, in particular, has not benefitted from modern
high-yielding crop varieties and farming practices as much as
other regions have.
Some potential biofuel
crops such as jatropha, cassava, sweet sorghum, may be able grow
on marginal land where food crops cannot strive. However,
growing any crop, including those that are drought resistant, on
land with low levels of water and nutrient inputs will result in
lower yields. It is therefore likely that
biofuels will intensify the
pressure on the fertile lands where higher returns can be
4.3 How will biofuel production affect water resources?
production, water is used in large quantities for washing plants
and seeds and for evaporative cooling. However, the biggest
impact on local water availability stems from
irrigation. Crops such as sugar cane, oil palm and maize have
relatively high water requirements and are best suited to
high-rainfall areas, unless they can be irrigated. Three
quarters of the sugar-cane production in Brazil and slightly
less of the maize production in the USA is rainfed.
The availability of water resources may constrain the
production of biofuel crops
in countries that would otherwise have a comparative advantage.
The amount of irrigation water needed in lower rainfall areas
can be significant. Many irrigated sugar-producing regions in
southern and eastern Africa and north-eastern Brazil are already
operating close to the limits of the available water. Even
plants like jatropha that can be grown in semi-arid areas may
require some irrigation during hot and dry summers.
Producing more biofuel
crops will also affect water quality. For
example, converting pastures or woodlands into maize fields may
increase problems of soil erosion and runoff of excess nitrogen
and phosphorous into surface and groundwaters. Pesticides and
other chemicals can also wash into waterbodies. Of the principal
feedstocks, maize is the
one requiring the greatest amount of fertilizer and pesticides
4.4 How will biofuel production affect soils?
Changes in land-use and intensification of agricultural
production both have the potential to harm soil condition, but
these impacts depend on the way the land is farmed.
Various farming techniques can reduce adverse impacts or even
improve environmental quality while still increasing
biofuel crop production.
These include conservation tillage and appropriate crop
Removing plant residues that would otherwise nourish the soil
and permanent soil cover that prevents erosion can reduce the
quality of soil. Only 25 to 33% of available crop residues from
grasses or maize can be harvested without detrimental effects on
soil quality, especially on soil organic content.
The use of perennial plants that can be harvested over several
years such as palm, short-rotation coppice, sugar cane or
switchgrass can also improve soil quality by increasing soil
cover and organic carbon levels compared with annual crops like
rapeseed, maize or other cereals. In the case of sugar cane,
soil quality can be maintained by applying nutrients from
sugar-mill and distillery wastes.
Crops such as eucalyptus, poplar, willow or grasses can be
grown on poor-quality land, and soil carbon and quality will
tend to improve over time.
4.5 How will biofuel production affect biodiversity?
Biofuel production can
affect wild and agricultural
biodiversity in some
positive ways, for instance through the restoration of degraded
lands, but many of its impacts will be negative, for example
when natural landscapes are converted into energy-crop
plantations or peatlands are drained.
Conversion of forest or
grassland for crop production has a significant effect on wild
biodiversity, because of
the loss of habitat. Many
current biofuel crops are
well suited for tropical areas, and this creates an economic
incentive to convert natural ecosystems into plantations causing
a loss of wild biodiversity in these areas.
For existing arable land, positive impacts on farmland
biodiversity can be
obtained by using crops which increase soil cover, avoiding
tillage and reducing fertilizer and pesticide inputs.
The genetic diversity of crops (agrobiodiversity) can be
compromised where large-scale production is practiced. Most biofuel
feedstock plantations are
based on a single species, using a narrow pool of genetic
material, with traditional varieties being used less and less.
Such low levels of genetic diversity increase the susceptibility
of crops to new pests and diseases.
feedstocks raise their own
concerns, since some of the proposed plant species can be
invasive. Similarly, care will be required when dealing with
genetically modified bacteria that produce enzymes used for
Crops which do well on fertile soils may not be as effective
in poorer conditions. For example, switchgrass performs less
well on poor soils than a diverse mixture of native grassland
perennial plants. In addition, such diverse mixtures can provide
better wildlife habitat,
water filtration and carbon sequestration than maize or soybean
4.6 How could an environmentally sustainable biofuel production be ensured?
The adoption of “good practices” in soil, water and crop
protection, energy and water management, nutrient and
biodiversity and landscape
conservation, harvesting, processing and distribution can
contribute significantly to making bioenergy
For instance, good agricultural practices, such as
conservation agriculture, and good forestry practices, can
reduce the adverse environmental impacts of
The environmental concerns about biofuel
feedstock production are
the same as for agricultural production in general, and existing
techniques to assess the environmental impact offer a good
starting point for analysing the biofuel systems. New
complementary methodologies are being developed to assess
bioenergy specific issues, for instance FAO’s analytical
framework for bioenergy and food security.
The development of
sustainability criteria or
standards as already under way in a number of fora, such as the
Global Bioenergy Partnership and the Roundtable on Sustainable
Biofuels, should be
established with the active collaboration of developing country
partners and go hand in hand with training and support for
Payments for environmental services may also represent an
instrument for encouraging compliance with
methods and standards.
Finally, for bioenergy to be developed sustainably, national
policies will need to recognise the international consequences
of biofuel development.