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Factsheet 1
Efficient Milk
Production
Climate Change
Greenhouse gases
and their effect on
our climate
Factsheet 1 Efficient Milk Production - Climate Change
Greenhouse gases and their effect on our climate
It is generally accepted that the earth is getting
warmer. Although there is some debate as to the
scale of the increase, most scientists believe that
this is the result of an accumulation of a number of
gases – the so-called greenhouse gases (GHGs) –
in the earth’s atmosphere. Changes in our climate
will have a direct effect on crop and livestock
production in the UK, but there are things we can
do now to help minimise the change in our climate.
The greenhouse effect
The earth’s temperature is kept stable by a blanket of gases that keep it warmer than it would otherwise be. These
act in much the same way as the panes of glass in a greenhouse. Solar radiation from the sun passes through the
atmosphere, and is absorbed by the earth, causing it to warm up. Part of the absorbed energy is reflected back,
in the form of long-wave radiation. Although some of this escapes into the outer atmosphere, some is retained,
resulting in an increase in the earth’s overall temperature (see diagram above)1.
The main gases responsible for this are water vapour, carbon dioxide (CO2), nitrous oxide (N2O), methane
(CH4), ozone and chlorofluorocarbons, and the extent to which the solar radiation is retained is determined by
their concentrations in the atmosphere. Although carbon dioxide is present in greatest concentrations, methane
and nitrous oxide are around 20 and 300 times, respectively, more potent than carbon dioxide in terms of their
greenhouse effect.
For many centuries, concentrations of GHGs have remained relatively stable, but human activities over the
last few centuries have resulted in increasing levels in the atmosphere. Scientists on the United Nations (UN)
Intergovernmental Panel on Climate Change (IPCC) have estimated that the earth’s climate has warmed between
0.6 and 0.9 0C over the past century, and that human activity is likely to have caused most of the increase in global
average temperature rises since the mid 20th century2.
The increase in GHGs, and their environmental implications, have been the focus of considerable international
attention. In 1997, the UN convened an international conference3 with the objective of establishing a legally
binding agreement, in which all the participating nations would commit themselves to tackling the issue of global
warming and reduce GHG emissions. The resulting Kyoto protocol set targets for an average reduction of 5.2%
in GHG emissions, based on 1990 levels, by the year 2012. Targets for individual countries varied, with the UK
agreeing a reduction target of 12.5%. As a signatory of the Kyoto protocol, the UK is committed to reducing
emissions of GHGs. In addition to its Kyoto targets, the UK Government has passed legislation that will bind the UK
to achieving a 60% reduction in CO2 emissions by 2050, with five-yearly reduction targets and an interim goal of
reducing CO2 by 26-32% by 2020.
This leaflet provides background information on the three gases that
are most directly affected by agriculture, namely methane, nitrous
oxide (and ammonia) and carbon dioxide.
Greenhouse gas emissions from agriculture
Methane (CH4): Although present at lower concentrations than
carbon dioxide, methane is about 20 times more potent than carbon
dioxide as a GHG, and in 2007 accounted for about 8% of the UK’s
Source: http://www.combatclimatechange.ie
Intergovernmental Panel on Climate Change (IPCC): Climate Change 2007: Synthesis Report
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The United Nations Framework Convention on Climate Change, held in Kyoto, Japan.
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GHG emissions. Nationally, emissions have declined by 53% since 1990 (Figure 1), largely due to reductions from
mining and landfill. In the same period, methane emissions from agriculture have declined by 17%. Farming still
accounts for more than 40% of all methane produced in the UK, and as a result the UK Government has given
a high priority to reducing methane emissions from agriculture. Ruminant livestock are responsible for most of
the methane, which is produced by rumen microorganisms as part of the normal digestion process, while lesser
amounts are produced from livestock manure management.
Nitrous oxide (N2O): Nitrous oxide emissions, weighted by
global warming potential, accounted for about 5 per cent of the
UK’s GHG emissions in 2007. Also known as laughing gas, it is
about 300 times more potent than carbon dioxide as a GHG.
Nationally, emissions declined by almost 50% between 1990 and
2007, largely due to reductions in industrial outputs (Figure 2).
Although nitrous oxide from agriculture reduced by 23% over this
period, it still accounts for around 75% of UK emissions. These
arise from the production and breakdown of fertilisers and manure
in the soil, and from manure management. A separate factsheet describes the origin of nitrous oxide emissions in
more detail, and mitigation options. Ammonia (NH3) emissions and nitrate leaching are indirect sources of nitrous
oxide so reducing these will also reduce nitrous oxide losses.
Ammonia (NH3): Although not strictly a greenhouse gas, ammonia released into the atmosphere dissolves in rain,
contributing to ‘acid rain’ and nutrient deposition on sensitive habitats. As such, it is an ‘indirect’ GHG, since its
deposition to land does result in nitrous oxide emission. It also represents a loss of valuable N from manure
and fertilisers.
Carbon dioxide (CO2): Emissions have been occurring as long as man has been burning solid fuels such as
wood, coal and peat. In the UK emissions peaked in the 1960’s, largely as a result of the use of fossil fuels (coal,
gas and oil) in power stations. Emissions from energy production and industry have declined by 14% over the last
20 years, reflecting the decline in manufacturing industries, while emissions from transport have increased by 11%
over the same period. Relative to these sources, agriculture accounts for a relatively small proportion of national
carbon dioxide emissions. The main sources of carbon dioxide emissions on dairy farms are from electricity and
fuel used for lighting, heating, cooling, cultivations and feeding etc.
The effects of increasing GHGs in the atmosphere
Scientists predict that rising concentrations of GHGs will result in an increase in the average surface temperature of
the earth. Although the full impacts of such temperature changes are unknown, speculation on the consequences
has been widely reported. For UK agriculture they include4:
• Increasing variability in winter rainfall;
• Higher temperatures in summer and autumn;
• L arger regional differences in temperature, with summer warming greater in the south-east than the north-west;
• Little change in overall rainfall, but wetter winters and drier summers;
• Changes in biodiversity, and the occurrence of new/exotic pests and diseases; and
• Rising sea levels, which will take some land out of production. These changes will clearly have an impact on the types of crops grown, their management and yields, and
ultimately what we feed to dairy cows. Globally, current trends in GHG emissions are predicted to have significant
and undesirable effects on human health, international trade and relations if they remain unchecked. It is clear that
all sectors, including agriculture, have a role to play in reducing GHG emissions.
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Source: Professor Chris Pollock: Predicting the Impact of Climate Change on UK Agriculture, The Impacts of Climate Change on Agriculture:
A Vision for Our Rural Landscape
Factsheet 1 Efficient Milk Production - Climate Change
Greenhouse gases: Options for UK agriculture
Overall, UK agriculture contributes approximately 7% of total GHG emissions. Although there have been significant
reductions in emissions from agriculture in recent years, further reductions need to be made if national targets are
to be achieved. At farm level, a number of strategies can be used to reduce emissions. These include:
1.Improving the efficiency of nitrogen (N) fertiliser and manure N use, by matching the amount of
N applied to crop requirements;
2.Increasing the productivity of farm livestock, so that emissions of nitrous oxide and methane associated with the maintenance requirements of livestock and rearing replacement stock, is spread over greater output (eg, milk and meat production).
3. Modifying livestock diets to reduce N excretion and methane emissions;
4.Adopting energy saving practices on farms, eg, replacing older machinery and buildings with more modern and more efficient equipment;
5.The use of anaerobic digestion, in which livestock manures and other inputs can be used to produce biogas (a mixture of carbon dioxide and methane);
6. Creating new woodlands to increase carbon storage in soil and plant biomass.
Some of these options will be more effective than others in reducing GHG emissions on farms, and may be
expensive to implement. The best option(s) may not be immediately obvious. It will be necessary to identify the
options that are most cost-effective on a farm-by-farm basis.
Putting a value on the benefits of reducing emissions on an individual farm basis is a complex process. Standard
emission factors for different processes associated with agriculture have been published5, and based on these a
number of companies and consultancies have developed software programs that calculate GHG emissions. Having
estimated sources of the different GHGs at a farm level, it is then possible to identify the most cost-effective ways of
reducing them.
The need to reduce GHG emissions is now universally recognised, and in common with other sectors, this will
provide increasing challenges – and opportunities - for UK farmers.
This is one in a series of six factsheets that have been prepared by ADAS, North Wyke Research
and the University of Reading for DairyCo.
Agriculture & Horticulture Development Board
Stoneleigh Park, Kenilworth
Warwickshire CV8 2TL
Tel: 024 7669 2051
Email: [email protected]
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Standards published by the Intergovernmental Panel on Climate Change (IPCC) and the British Standards Institute (PAS 2050) are the most
widely recognised and used in the UK.