Emissions of carbon dioxide (CO2) accounted for 61.0% of the national total GHG emissions (excluding LULUCF) of 61,528.09 kt CO2 equivalent in 2021, with CH4 and N2O contributing 27.9% and 9.9%, respectively. The combined emissions of HFC, PFC, SF6 and NF3 accounted for 1.2% of total GHG emissions in 2021. In 1990 emissions of CO2 accounted for 59.9%, CH4 28.5% , N2O 11.8% and the combined emissions of HFCs, PFCs, SF6 and NF3 were less than 0.1%, of total emissions of 55,240.87 kt CO2 equivalent.
Carbon dioxide CO2 is the most significant contributor to the greenhouse gas emissions. The energy industries and transport sectors are responsible for 26.8% and 28.8% of total CO2 emissions (excluding LULUCF) in 2021, respectively. The residential sector has an 18.3% share, manufacturing combustion has a 12.2% share and the remainder of CO2 emissions (13.9% share) fall into other categories. Emissions of CO2 increased from 32,944.4 kt in 1990 to 37,502.2 kt in 2021, which equates to an increase of 13.8%. The main driver behind this increase in emissions is fuel combustion in the transport sector (+114.5.2%) over the period 1990-2021.
Methane CH4 is the second most significant contributor to greenhouse gas emissions in Ireland and is due to the large population of cattle.
In 2021 estimated emissions of CH4 were 17,182.29 kt CO2eq, indicating an increase of 9.3% on the 1990 level of 15,719.24 kt CO2 equivalent. Emissions of CH4 increased progressively from 1990, reaching a peak in 1998 of 17,499.95 kt CO2eq - This reflects an increase in livestock numbers and therefore increased emissions from source categories, enteric fermentation and manure management. Between 1998 and 2011 CH4 emissions decreased due to falling livestock numbers from reforms of the Common Agricultural Policy (CAP). The main contributor to the CH4 trend has been the agriculture sector and in 2021 this sector accounted for 93.6% of the total CH4 emissions (compared to 85.8% share in 1990 when emissions from waste sector had a larger share in the level). The sectoral CH4 emissions from agriculture increased by 19.3% between 1990 (13,482.07 kt CO2 equivalent) and 2021 (16,086.10 kt CO2 equivalent).
Another significant source of CH4 emissions is the waste sector, especially from landfill gas in the sector solid waste disposal on land. CH4 emissions from waste decreased from 9.8% share of total methane emissions (1,545.85 kt CO2eq) in 1990 to 4.6% share (797.81 kt CO2eq) in 2021. This decrease is a result of improved management of landfill facilities, including increased recovery of landfill gas utilised for electricity generation and flaring.
Nitrous oxide N2O emissions decreased by 6.7% from their 1990 level of 6,541.69 kt CO2eq ito 6,106.21 kt CO2eq in 2021. Like CH4, emissions of N2O increased during the 1990s to reach peak level of 7,361.58 kt CO2eq in 1998 reflecting increased use of synthetic fertilisers and increased amounts of animal manures associated with increasing animal numbers over that period. Emissions of N2O subsequently show a clear downward trend following reductions in synthetic fertiliser use and organic nitrogen applications on land because of CAP reform on animal numbers as well the closure of Ireland’s only nitric acid plant in 2002. However, in six of the last seven years of the GHG inventory (2015-2021) N2O emissions increased, as the dairy sector expanded, and nitrogenous fertiliser use increased.
The largest contributor to the trend is the agriculture sector with 93.6% share of the total N2O emissions (5,716.74 kt CO2eq) in 2021. This reflects an increase from 82.5% share (5,396.36 kt CO2eq) in 1990. Emissions from the industrial processes chemical industry used to be the second largest contributor to the trend. They contributed 13.9% to the total N2O emissions in 1990 and an average of 11.0% share to the trend between 1990 and 2000, before falling to a 4.5% share in 2002 – the year the nitric acid plant closed. Thereafter, the average share equated to 0.6% of total national emissions.