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It’s December and the last of the autumn leaves are
still clinging to the oak trees outside the VEGA office window.
Later autumn, hotter summers, and wetter winters have all
been put forward as examples of global warming here in the
UK. Human activities are causing the release of huge quantities
of “greenhouse gases” into the atmosphere and it
seems increasingly likely that this is the cause of the rising
global temperatures and climate changes taking place. The
six greenhouse gases are (in order of importance): carbon
dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons,
and sulphur hexafluoride.
In the UK the government is monitoring and reducing all greenhouse
gas emissions in line with the Kyoto agreement. The progress
so far has been to reduce total emissions by about 9% per
year between 1990 and 1998 (Government Report on Climate Change:
Delivering Emission Reductions, 2000. The full report can
be found at www.defra.gov.uk /environment/climatechange/cm4913/pdf/section2.pdf)
Table of Greenhouse Gas Emissions From Agriculture in
the UK
The figures in the Table above show the emissions
of the three major greenhouse gasses: CO2 is the biggest offender
in the UK, as in the rest of the world, and even with considerable
efforts at reduction the UK’s CO2 emissions are predicted
to be 160.7 MtC* in 2020.
*Greenhouse gas emissions are expressed
as million tonnes of carbon equivalent (MtC). One tonne of
carbon is equivalent to 3.7 tonnes of CO2. The greenhouse
gases vary in their capacity to warm the atmosphere, i.e.
each gas has a different global warming potential (GWP). The
emissions of methane and nitrous oxide have been multiplied
by their GWP, then divided by 3.7 to give a comparable figure.
Transport and power supply are the two biggest sectors producing
greenhouse gases in the UK (see pie chart below), but agriculture
accounts for a significant portion (12%) of our total emissions
 The
burning of fossil fuels is the major source of CO2 . In a
recent report by ADAS (Project OF0182) the energy input per
tonne of yield for various crops was calculated. Energy requirements
for collection, distribution, crop drying, fertilizers, pesticides,
machinery inputs, and seed were assessed. In a comparison
of organic versus conventional crop production the total energy
input for organic crops was found to be significantly lower,
mainly due to reduced (or zero) use of fertilisers and pesticides.
Even though the energy costs for distribution or for farm
machinery use were often higher for some organic crops overall
they were more energy efficient. The manufacture and transport
of fertilizers and pesticides account for 50% of the input
into conventionally grown potato and winter wheat crops, and
up to 80% of the input into some vegetable crops. Environmental
R&D Newsletter, February 2001). Glasshouse horticulture,
not surprisingly, is the highest agricultural energy user
in the UK.
If you buy imported organic fruit and veg any reduction in
carbon dioxide emissions from avoiding use of fertilizers
and pesticides are clearly negated by the huge energy costs
of transport, but reduction in the use of chemical inputs
in farming does have other environmental benefits.
“Food miles” is the term used for the distance
food travels from farm to fork and this is the focus of much
attention from various environmental organizations. In the
UK self-sufficiency in foods is decreasing. In 1989-91 the
UK was 85.1% self-sufficient in indigenous food types, compared
to 79% in 2000 (DEFRA figures). Both imports and exports of
food are increasing.
Global methane emissions from anthropogenic sources include
those from the oil, coal and gas mining, landfill sites, sewage
disposal, and deforestation as well as agriculture. However,
in the UK the total emissions of methane in 2000 were 14.3
MtC, of which agriculture accounted for 5.7 MtC. Agriculture
is obviously an important source of methane emission in the
UK, and most of this arises from livestock farming. Ruminants
produce some methane from the fermentation of food in their
gut and decomposition of manure accounts for the rest.
Pig and dairy farming produce large amounts of methane due
to the intensive farming methods, with high animal densities
and the anerobic decomposition of slurry. In free-range livestock
systems manure on pasture is more likely to decompose aerobically
and so less methane is produced. According to government figures
methane emissions per litre of milk produced have decreased
in Europe by around 30% over the past 40 years due to increased
milk output per cow and a more digestible diet for cattle.
Nitrous oxide (N2O) is the third important greenhouse gas.
Industrial sources are being reduced, making agriculture increasingly
important. Total emissions for UK for 2000 were 11.2 MtC,
of which the contribution from agriculture was 7.5 MtC, i.e.
over two thirds. As for methane, emissions of nitrous oxide
come from farmyard manure and slurry, housed livestock and
their waste and from the use of artificial fertilizers on
the land.
Measurements and predictions of greenhouse gas emissions
are difficult, but according to government estimates (see
Table 1) emissions of methane and nitrous oxide from agriculture
are not predicted to decrease by year 2020, in fact they will
rise slightly.
Intensive livestock systems are the major source of agricultural
emissions of these two important greenhouse gasses.
Worldwide agriculture and food production processes are contributing
to the production of greenhouse gasses. Fertilizer and pesticide
manufacture and transport, use of farm machinery, processing
and packaging food, and the import and export of food, feed
and ingredients are all dependent on burning fossil fuels
creating carbon dioxide emissions, while use of fertilizers
and livestock farming produce methane and nitrous oxide. Methane
is also produced from growing rice in paddy fields, not to
mention the waste food rotting in landfill sites. Further
carbon dioxide is produced when land use is changed from grassland
to arable, or fenland is drained, as well as from timber harvesting.
Current agricultural and food production practices are a significant
contribution to the problem of greenhouse gas emissions, but
farming of fuel crops may become at least a part of the solution.
Renewable energy crops such as short rotation coppice woodland
could help reduce our greenhouse gas emissions. For example,
Project Abre in Yorkshire will be the first wood fuelled power
station in Great Britain. There are already two plants in
Ireland burning willow and delivering electricity to the grid.
Energy from burning biomass results in 60-75 grams of carbon
dioxide emissions for each kilowatt hour. Most of this CO2
is from the use of fossil fuels in the production and transport
of the wood. A natural gas power plant emits 400-500 grams
of CO2 per kilowatt hour, and a coal-fired power station 950-1300
grams per kilowatt hour.
Continued planting of woodland in agri-environment schemes
(see article below) can also provide longterm “sinks”
for some of the CO2 currently being produced, although the
CO2 will be released when the tree is felled.
Sylviculture
There are now 25 trees for every person in England, and 8.4%
of the countryside carries a cover of trees; in 1870 the coverage
was estimated at 4.8% and in 1980 (just after the launch in
1976 of the Green Plan) it stood at 7%. In 1086 the coverage
was 15%; England has for long been low in forest cover, and
very low in comparison with the average over Europe of 36%.
Surrey is the most densely wooded county in England, with
over a fifth of its land area covered with trees. The southeast
corner of Britain has always had more trees than the rest
of the UK, with 14% of the land area in woodland; the Yorkshire
and Humber area has only 6%.
Spare That Tree
Oak has become England’s commonest tree species and
the numbers of trees continue to rise, reversing the devastations
of the gales of 1987 and the effects of Dutch elm disease.
The number of conifer plantations has been falling and the
Forestry Commission could proclaim at the start of National
Tree Week in November 2001 a change of policy – from
planting ranks of closely-packed fir-trees for timber-production
to open mixed woodland, mostly of broad-leaved trees, to provide
recreation, access, tourism, and for wildlife, as well as
for timber. Previously industrialised areas of the Midlands
are being returned to forestry. Farmers are able to get grants
for planting trees on set-aside land.
Scotland and Wales are not surveyed similarly. Most of the
plantings in these areas are conifers in forest. In England
ash, sycamore, and sweet chestnut have been extensively planted.
These developments illustrate Green Planning that could be
easily overlooked in the rush to complete the Farming and
Food Commission’s deliberations. VEGA keeps an eye on
these issues and the environmental corollaries. Food-production
from trees is not reckoned with, although hedgerows are an
already under-exploited native resource for nuts and berries
for food and drink.
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