Greenhouse Gas Inventory 2023: New Calculation Guidelines Leave Overall Picture for Agriculture Largely Unchanged

Agroscope compiles annually updated inventories and projections for Swiss agricultural greenhouse gas emissions. With the change to reporting under the Paris Agreement, new bases for calculation must be taken into account. Despite this, the overall picture for agriculture remains largely unchanged.

The agriculture and food sector is a major source of greenhouse gas emissions in Switzerland. According to the sectoral distribution for national inventories, agriculture’s share of GHG emissions in 2020 was 13.3%. In the second commitment period of the Kyoto Protocol (2013-2020), these emissions were a good 10% lower than in 1990. In order to meet the long-term climate targets of the Swiss Confederation, a redoubling of efforts will be needed. The national inventory serves as an important foundation for this.

New international calculation standards

Under the Framework Convention on Climate Change, a crucial change in greenhouse gas reporting occurred this year. The previous provisions of the Kyoto Protocol are being superseded by the respective regulations under the Paris Agreement. Firstly, this means that new general reporting guidelines are being adopted. These include the revised global warming potentials (GWP) of the Fifth Assessment Report of the IPCC, which attribute a slightly higher significance to methane and a slightly lower significance to nitrous oxide than previously. Secondly, an update to the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories occurred.

Adjusting the calculations to Swiss conditions

Based on ongoing research on agricultural substance- and energy-flows, numerous methods and calculation factors have been continuously adapted to Swiss-specific circumstances and kept up to date with the latest knowledge. The calculation models are therefore less dependent on the standard methods and factors of the international guidelines. This explains why the new guidelines only result in small changes for the agricultural sector in the Swiss Greenhouse Gas Inventory. The most significant changes are:

• Nitrous oxide emissions from animals during grazing are significantly lower than previously calculated;
• Indirect nitrous oxide emissions due to nitrate leaching or run-off are higher than previously calculated;
• Methane rates during the digestion of feed (enteric fermentation) in growing cattle were reduced slightly;
• Feed digestibility was increased for various animal categories, resulting in lower methane emissions from manure management;
• Due to slightly higher normal values for ambient temperatures, estimates for methane emissions from slurry storage increased slightly.

Lower nitrous oxide emissions during grazing are of low relevance for overall emission totals

Possibly standing out as a relevant new development are the substantially lower nitrous oxide emissions during grazing. Previously, it was assumed that very high nitrous oxide emissions resulted from the deposition of large amounts of urine-nitrogen over a small area during grazing. More-recent measurements, however, have shown that the emission factors are considerably lower than the international standard factors previously used. This alleviates the previous trade-off between ammonia and nitrous oxide emissions on pastures. Nonetheless, the overall effect on total agricultural emissions is small, due to the relatively small contribution of emissions from pasture (Fig. 1). In conclusion, there are very few new findings with regard to recommendations for farmers and policy-makers.

Fig. 1: Comparison of agricultural greenhouse gas emissions between the reporting guidelines in 2022 (previous calculation method) and 2023 (new calculation method); by way of example, the emissions from 2020 are compared here, whereas the recalculation is always applied to the whole time series back to 1990. Adjustment of global warming potentials (GWP): The GWP of nitrous oxide (N₂O) and methane (CH₄) were updated in 2023.