Arbejdsrapport fra Miljøstyrelsen 5/2007 – Konsekvenser og muligheder ved Danmarks deltagelse i Kyoto-protokollens artikel 3.4 på landbrugsområdet

Konsekvenser og muligheder ved Danmarks deltagelse i Kyoto-protokollens artikel 3.4 på landbrugsområdet

Summary and conclusions

Denmark has a commitment under the Kyoto Protocol to reduce the emissions of greenhouse gases by 21% from the reference year 1990 until the commitment period 2008-12. Emissions of methane and nitrous oxide from the agricultural sector are included in the national greenhouse gas inventories and thus also in the reduction commitment, and this is also the case for use of fossil fuels in production. This is, however, not the case for those contributions to the CO₂ balance, where net emissions can be ascribed to changes in cultivation of agricultural crops and grasslands (article 3.4 under the Kyoto Protocol).

The contributions under article 3.4 of the Kyoto Protocol concern changes in the carbon (C) storage in vegetation and soil. The fluxes of C to and from biomass and mineral soils must, under the Kyoto Protocol, be calculated on the basis of a net-net principle, where the net emissions are calculated as the rate of change in the C storage in the commitment period (2008-12) minus the rate of change in the reference year (1990). The rate of change can be estimated in different ways, but the method must be the same in the commitment and reference years. The following sources and sinks are included under the article 3.4 for agriculture:

Net changes in C storage in mineral soils as affected by changes in land use and agricultural practice.
Net changes in C storage by drainage and cultivation of organic soils or by re-establishment of wetlands.
Changes in C storage in trees in shelterbelts and fruit plantations.
Emissions of CO₂ from application of lime to agricultural land.

The implementation of article 3.4 of the Kyoto Protocol has been described in the decisions of the COP7 meeting in Marrakesh. These decisions can be summarised as:

The inventories cannot include removal of CO₂ from the atmosphere, which is a result of (a) increased CO₂ concentration in the atmosphere above the pre-industrial level, (b) indirect nitrogen deposition, and (c) the dynamic effects of age structures, which result from activities and practices before the reference year (1990).
The inventories must be performed in accordance with IPCC guidelines for national emission inventories, in particular the Good Practice Guidance for LU-LUCF.
The following areas can be either included or excluded: Forest management, Cropland management, Grazing land management and Revegetation.
The reporting must document that changes in emissions are due to human-induced activities after 1 January 1990.
When a land area is included under article 3.4, it must remain there in future commitment periods.
The national emissions inventory must ensure that land areas under article 3.4 are identifiable.
The inventories will be reviewed in accordance with article 8 of the Kyoto Protocol.

The emissions inventory under land use for the UNFCCC is subdivided in six main areas: forestry, cropland, grazing land, wetlands, built areas and other, which mainly refer to ice-covered lands, rocks and non-classified areas. These six areas must constitute the total Danish area. The information currently available does not allow a subdivision of the Danish area into these six classes to be performed with sufficient accuracy, and it is also not possible to assess changes over time since 1990 with sufficient accuracy. It is assumed here that there is no change in C storage in natural areas, built areas and other land areas. It is also assumed that C storage in forest soils are considered elsewhere. Since the majority of grasslands in Denmark are included in the normal agricultural practice, these agricultural grasslands will be treated as cropland. This also includes permanent pastures used for agricultural purposes.

In the accounting of changes in C storage of cultivated soils, there is a distinction between mineral soils and organic soils. The IPCC guidelines use a threshold of 20% organic matter to distinguish these groups. This deviates from the Danish soil classification, which uses a threshold of 10%. It has therefore been necessary to estimate the proportion of organic soils with a content of 10 to 20% organic matter, and these soils are here treated as a special group of mineral soils. The accounting of changes in soil organic matter in mineral soils have been performed using a dynamic model, which includes modelling the effects of C additions to the soil and turnover rate of C in the soil, including the effects of soil tillage and climatic conditions.

The estimates of C storage in mineral soils show large differences before and after the prohibition of field straw burning, which was implemented in 1990. There was a simulated decline in soil C storage in the period up to 1990, whereas the content was almost unchanged in the period after 1990. There is a large inter-annual variation in the CO₂ emissions, both as a consequence of climatic variation and of variation in crop yields. It is therefore in accordance with the Good Practice Guidance to use a 5-year moving average to estimate the net emissions in the reference year. This will reduce the effect of the inter-annual climatic variability, but also even out the effect of the ban on straw burning. This ban was put into force from 1 January 1990, and the effect of such a measure should, according to the Good Practice Guidance, be counted from the time when it has an effect in the inventories in situ. The effect of the ban against burning of straw can therefore probably be included from harvest (August) 1990 and therefore included as a part of fulfilling the Kyoto commitment.

The CO₂ emissions from organic soils with more than 20% organic matter were calculated in 1990 at 1.15 mil. t CO₂/year with a decline to about 1.05 mil. t CO₂/year in 2008-12, primarily as a result of a reduction in the agricultural area. The setting up of new shelter belts had almost no net effects on emissions in 1990, but a net C sequestration in 2008-12 of about 0.17 mil. t CO₂/year. Fruit trees and bushes had only a marginal contribution to the inventory. The use of lime has been greatly reduced over the past 15 years, which has resulted in a reduction in net emissions from 0.57 mil. t CO₂/year in 1990 to 0.22 mil. t CO₂/year in 2008-12.

The adoption of article 3.4 will lead to increased emissions in the reference year of 3.28 mil. t CO₂/year from agricultural land use. During the period 2008-12 there will be an estimated uptake of CO₂ in mineral soils of 0.35 mil. t CO₂/year, which in comparison with the reference year leads to an estimated uptake in mineral soils of 1.89 mil. t CO₂/year. There are also considerably lower emissions from the other components in the inventory, and the result is a total estimated reduction during the period of 2.53 mil. t CO₂/year. These elements are not included in the calculation of the Assigned Amounts (AA) according to articles 3.4, 3.7 and Annex A of the Kyoto Protocol, and the calculated emission in the base year therefore does not lead to an increase in the Danish AA. The immediate effect of an inclusion is therefore a reduction of the Danish reduction commitment of 2.53 mill. t CO₂/y. This estimate is, however, conditioned by a temperature during the commitment period (2008-12) that is identical to the climate during the normal period 1961-90. If a temperature increase of 0.02-0.03 °C/year since 1990 as a consequence of climate change is included in the estimates, then the net emissions from mineral soils are increased by 0.39-0.59 and 0.54-0.81 mil. t CO₂/year in 2008-12 and 2025, respectively. The effect of anticipated climate changes will therefore reduce the net effect of adopting article 3.4 for Cropland Management to 1.94-2.14 mil. t CO₂/year in the first commitment period. This may be reduced to 1.14 mil. t CO₂/year, if the projections in stead are based on the very warm years of 2001 to 2004. The uncertainties in this estimate due to future changes in land use are in the order of 0.3 to 0.4 mil. t CO₂/year.

Because the emissions from mineral soils are a 5-year average based on actual harvest yields and climate, it is not possible to estimate the final contribution to the Danish reduction commitment before 2014-15. The minimum contribution is assumed to be 0.5 mil. t CO₂/year in 2008-12. However, a combination of two years with poor harvests and two warm winters in 2008-12 will reduce this amount further.

The estimations show that some changes in agricultural practises and land use may reduce the emissions and others may increase the emissions. Reduced emissions, especially resulting from an increased area with permanent pastures, catch crops in the autumn and a reduction of organic soils in rotation will at best reduce the emissions by 1 mill. t CO₂/year in 2008-12. Increased emissions will take place if the area with grass is reduced, removal of straw from the field is increased, and if there is more burning of slurry and solid manure and more growing of non-food crops on set-a-side areas. In total it is assumed that the maximum increase will be an app. 0.5 mill. t CO₂/year in 2008-12.

Changes in agricultural practices may therefore both increase and decrease the emissions. There are no projections of land use to indicate that the emissions will increase or decrease. The uncertainty of the estimate of emissions is therefore estimated at 0.3 to 0.4 mill. t CO₂/year as a consequence of uncertainties in changes in agricultural practices.

A scenario with a continuous increase in the average temperature of 0.3 °C per 10 years and no changes in agricultural practices shows that cropland management and grassland management may contribute with app. 1.94 mill. t CO₂/year to the Danish reduction commitment. The most likely contribution from crop management and grass management on the Danish emissions reduction commitment may therefore be estimated at 1.6 to 2.3 mill. t CO₂/year in 2008-12.

The effect of adopting article 3.4 of the Kyoto Protocol for agricultural land in future commitment periods will depend on whether the net-net principle is continued for mineral soils, and which reference year is used. If the reference year is still 1990, then it will probably be possible to continue to argue for a net reduction in emissions. This will be much more difficult if net emissions in the reference year cannot be subtracted, or if a later reference period is chosen. The effect of future climate changes will also play a major role for the size of net emissions from agricultural land use.

The adoption of article 3.4 will increase the demands on reporting considerably as there are increased demands on inventories of land use and demands for verification of model estimated changes in soil C storage. For Denmark this problem may be solved by making use of satellite imagery for assessing land use changes, soil sampling to determine change in soil C storage, implementation and documentation of a total model system and of databases and administrative routines. This can probably be implemented for DKK 52 to 68 mill. To improve the inventory for future commitment periods there is a demand for a research effort costing about DKK 15 to 37 mill.