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Agriculture and climate change
Alessandra SENSI (Eurostat)
Although agriculture accounts for
only 9% of greenhouse gas emissions, it is the main source of methane (CH4), and nitrous oxide (N2O) emissions. On the other hand, conversion of
agricultural land to forest offers considerable potential to absorb CO2 from the atmosphere.
The Kyoto protocol: an overview
Global warming and climate change are currently a major environmental issue at international level. New commitments to reduce emissions of GHGs beyond the year 2000 were agreed in Kyoto in December 1997, under the UN Framework Convention on Climate Change (FCCC) first signed in 1992.
The Kyoto Protocol, adopted by consensus by the some 150 parties, stipulates that Annex 1 Parties (mainly industrialised countries) shall individually or jointly reduce their aggregate emissions of a "basket" of six greenhouse gases to 5% below 1990 levels in the period 2008-2012. The gases concerned are: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), HFCs (hydrofluorocarbons), polyfluorocarbons (PFCs) and sulphur hexafluoride (SF6).
For its part the European Union undertook to cut emissions by 8%, compared with 7% for USA and 6% for Japan and Canada. On the other hand, Australia is allowed to increase emissions by 8%. Although no emission reductions were fixed for developing countries, the Protocol establishes a "clear development mechanism" in order to channel private funds into developing countries for the emission reduction credit purchases.
The Protocol specified for the first time that GHG targets should be for net emissions, i.e. should take into account not only emissions of GHGs, but also removals by sinks which are the result of man-induced land use change and forestry activities (afforestation, reforestation, deforestation) since 1990. Modalities, rules and guidelines for including sinks have still to be defined.
A further option to trade "emission permits" among industrialised countries for the purposes of meeting their targets was included, but is considered supplementary to domestic actions. This will increase the importance of developing reliable methodologies for calculating emissions and sinks.
What is the greenhouse effect?
The greenhouse effect is a natural phenomenon largely responsible for life on earth as we know it. This phenomenon is caused by the layer of atmosphere (gases) which absorbs and re-radiates infra-red radiation from the earths surface. Human activities, such as combustion of fossil fuels and intensive livestock breeding, are altering the composition of gases in the atmosphere, causing heat which would normally be radiated out to be retained. Although the consequences of this are not as yet fully known, the consensus is that the effects will include global warming and climate change (IPPC, 1996). As a consequence, an extra warming of the surface and the lower atmosphere is expected, leading to disturbances in the geosphere/biosphere system and notably, an increase in the mean global surface temperature and in the mean sea level, as well as extreme weather patterns. This could have serious implications for agriculture (ex. inhibition of plant growth), which more than any other sector is very dependent on weather conditions.
Even though the actual emissions of some greenhouse gases such as methane and nitrous oxides are relatively small, some are more powerful than others, i.e. they cause more heat to be retained. This is referred to as Global Warming Potential (GWP). So, for example, over a twenty year period, one kg of methane will have the same effect as 56 kg of CO2. Because CH4 and N2O breakdown slowly in the atmosphere, the GWP varies depending on the time scale considered (Table 1).
Agriculture as a source and sink of Greenhouse gases
Agriculture is estimated to be responsible for 9% of total greenhouse gas emissions (Figure 2 andTable 2). It is a major source of CH4 and N2O, with latest estimates showing that it accounts for 48% of CH4 emissions and 52% of N2O emissions in the EU (Figure 3). The role of agriculture - both as a source of and as a sink 2 for greenhouse gases (GHGs) - varies significantly across Europe because of the different agricultural policies adopted and the different agricultural practices implemented.
Guidelines for National Greenhouse Gas Inventories have been drawn up by the Intergovernmental Panel on Climate Change (IPCC). These Guidelines (IPCC 1996) distinguish between "Agriculture", and "Land Use Change and Forestry", as follows:
These definitions will also be used in this text.
In 1996 no country reported CO2 emissions from Agriculture (Table 3). However the picture changes if Land Use Change and Forestry are included, although few countries provide data on emissions of CO2 for this category. In fact, most countries estimate that removals of CO2 exceed emissions for the Land Use Change and Forestry category, and report only net figures, i.e. removals minus emissions. From the data on emissions which have been supplied, (France, Italy and UK) it can be seen that CO2 emissions amount to at least 24% of total GHG emissions from these two categories (Figure 4).
Only three countries have declared emissions of CO2 under Land Use Change and Forestry. The remaining have reported the balance between removals and emissions which generally results in net removals. These are therefore reported as sinks.
Agriculture generates greenhouse gases
According to the latest figures for 1996, agriculture is the main contributor to CH4 emissions (43%), followed closely by waste (34%) and energy (21%) (Figure 5).
Within the category "Agriculture", the major sources of emissions are enteric fermentation and manure management, which, in 1996, accounted for about 71% and 24% of the total CH4 emissions resulting from agricultural activity (Table 4).
The amount of methane emitted by livestock is calculated as the number of animals multiplied by an emission rate per animal. The emission rates mainly depend on the type of digestive system of the animal and its feed intake.
Livestock manure is mainly composed of organic matter that, in the absence of oxygen, is decomposed by methanogenic bacteria and in this way produces methane. The main factors involved in the calculation of methane emissions due to manure management are the amount of manure produced and the proportion of manure that decomposes anaerobically. The first factor is linked to the type and number of animals, whereas the second is strongly dependent on climate and on manure management practices, particularly storage of manure.
As far as the other sources of emissions are concerned, either they are not relevant issues at European level (rice management, burning of savannas) or their contribution to CH4 emissions is quite low (in1996, 3% from agricultural soils and only 0.3% for field burning of agricultural residues).
For Land Use Change & Forestry, almost 97% of the emissions are attributed to "Other Land Use Change Activities", which refers to activities such as shifting cultivation, flooding and wetland drainage. However, to date these flows and the related magnitude are not well determined. (Box1)
Nitrous oxide emissions (N2O)
Agriculture is also the main source of N2O emissions and is responsible for some 52% of total N2O emissions, compared with 27% due to Industrial Processes, 16% to Energy Use and 4% to Land Use & Forestry (Figure 6).
N2O emissions from agriculture can be divided into 1) direct emissions from agricultural soils and from animal production systems, 2) indirect emissions which take place after nitrogen is lost from the field as NOx or NH3 or after leaching or runoff of nitrates, and 3) emissions resulting from agricultural burning.
As shown in the table 5, the main source is represented by item D "Agricultural Soils" (about 94% in 1996). This includes emissions from manure after spreading on soils but excludes the emissions due to manure handling. The latter are included under a specific item "Manure management" which in 1996 accounted for 6% of N2O emissions.
Within the sector "Land Use Change & Forestry", Other Land Use Activities are by far the major source of N2O emissions.(Box2)
Carbon dioxide (CO2) emissions
In 1996 no EU country reported emissions of CO2 from the sector "Agriculture", and only three countries, France, Italy and United Kingdom, reported emissions under "Land Use Change & Forestry". The other Member States reported only net removals, i.e. CO2 removals minus emissions.
In 1996, 66% of these gross emissions were due to "Changes in Forests & other Woody Biomass Stocks", 25% to "Forest and Grassland Conversion", and 8% to emissions from soil and other sources.
The use of fossil fuels for machinery and heating in the agriculture sector also produces CO2 emissions. These are included in category 1 "All Energy Use", and not in category 3 "Agriculture". Eurostat estimates put the percentage of energy related CO2 emissions due to Agriculture in the EU at 1.6% 3(Figure 7 and Table 6). However this is considered an underestimate as it is often difficult to separate fuel used in agriculture from that used in other sectors (box 3).
Agriculture and forestry can remove greenhouse gases
There is still considerable discussion on the estimation of the quantities of greenhouse gases absorbed from the atmosphere as a result of agricultural and land use change activity. To date, no common IPCC methodology has been adopted and countries currently apply their own methods with the result that the estimated emissions (Table 6) are of uncertain quality. Potential sinks of GHG are given briefly below, by gas:
As can be seen from the figures in table 6, the principal sink for CO2 is forest, as young trees have a considerable potential to absorb CO2 over many years. Similarly, the reversion of agricultural land to uncultivated grassland may result in carbon sequestration. Other sinks of CO2 in soils are associated with changes in the amount of organic carbon stored in soils.
Soil sinks for N2O
Aerobic soils are typically sources of N2O, but small uptake rates have been observed in isolated instances in dry soils and wet grass pastures. Theoretically, anaerobic soils have a large potential for reducing N2O to N2, since the major product of denitrification in soils is usually N2 rather than N2O. However, no large or constant N2O uptake has been reported. Until additional information is available to indicate that soil uptake is important, soil uptake of N2O will not be included in the N2O budget for agricultural systems.
The role of agriculture as a sink of CH4 should also be mentioned. The oxidation of atmospheric CH4 by well-drained soils accounts for approximately 10% of the global CH4 sink. The ability of soil to produce or consume CH4 depends on the land use and the type of soil. Dried, uncultivated soils and pastures may absorb CH4. Cultivated soils on their own are not an important source or sink of CH4, though numerous studies have shown that the application of nitrogenous fertilisers to soils frequently inhibits CH4 oxidation, i.e. that ammonia acts as inhibitor of the enzyme which oxidizes CH4 to CO2.
In 1996 "Changes in Forest and Other Woody Biomass Stocks" accounted for 86% of reported removals of CO2, 2% was attributed to "Abandonment of Managed Lands" and 11% to "Other Land Use Change Activities".
For France, Italy and United Kingdom, the figures in table 7are gross emissions, whereas the other countries have given net removals for the "Land Use Change and Forestry sector", i.e. removals of CO2 minus emissions of CO2. The net removals for 1996 for France, Italy and UK are 35 897, 24 255 and -19 347 thousand tonnes, respectively. The large difference seen for Germany between 1990 and 1996 is because flood and storm damage was exceptionally high in 1990. The resulting removal of fallen trees from forests is reflected in a very low figure for net CO2-absorption for Germany 1990.
Expected impacts of climate change on agriculture
Under the Environment and Climate Programme of the EUs Fourth Framework Programme for Research and Development, a number of studies of climate change impacts have been carried out. The most recent results from these projects are described below.
Sea-level change in Europe
Sea surface levels around the coasts of the European Union are currently rising at a rate of between 1 and 1.5 millimetres per year. An increase in storminess has been observed in most of the North-East Atlantic and in the North Sea during the last few decades. This combination may result in larger areas being susceptible to flooding in future years, with potentially disastrous effects on harvests.
Ongoing EC-funded projects are examining the implications of climate change on water resources in Europe, in particular on water availability, flow regimes and drought. Although annual rainfall amounts are expected to change little, models predict considerable intra-annual variability, generally with increased winter rainfall, and longer summer dry-spells. There is a growing realisation of the problem of desertification in European countries, especially in the Mediterranean area. In Southern Europe large increases in potential evapo-transpiration leading to depletion of groundwater aquifers are expected. This could result in irrigation being curtailed in the summer periods, which may affect irrigated intensive horticultural crops.
Climatic variability experienced during recent years has already led to dramatic water shortages, erosion, landslides and harvest losses. These threats may be aggravated by even relatively small shifts in climate conditions, which would hinder rather than sustain water supplies and agricultural productivity.
Relatively small changes in climate can have significant impacts on agricultural productivity. Current differences in crop productivity between northern and southern Europe are likely to increase under climate change. Exceeding crop-specific high temperature thresholds may result in a significantly higher risk of crop failure in parts of southern Europe, while northern Europe may be able to grow a wider range of crops than is currently possible, due to a warmer and longer growing season. Crops which are presently grown throughout Europe experience more positive impacts in northern Europe compared with southern Europe.
The inter-annual variability of crop yields is particularly sensitive to changes in climatic variability. In regions where crop production is affected by water shortages, such as in southern Europe, increases in the year-to-year variability of yields in addition to lower mean yields are predicted. Adaptive strategies, such as changing variety and altering sowing date, may alleviate yield losses by reducing the risk of low yields in some situations.