Alan Matthews: Price incentives needed to reward farmers who take decisive climate change actions
Agricultural emissions in Ireland are largely a methane problem associated with ruminant livestock production. Total agricultural emissions measured in tonnes of carbon dioxide equivalent (CO2 eq) amounted to just over 20.2m tonnes in 2017, or 33pc of total national emissions.
Around 13m tonnes of this are due to methane arising from enteric fermentation (11.5m tonnes CO2 eq) and manure management (1.5m tonnes). The remaining 6.3m tonnes are accounted for by the release of nitrous oxide following the application of manure and fertiliser to agricultural soils.
Total methane emissions from agriculture rose in the period 1990-1998, then fell in the period to 2011 after which they started to rise again. In 2017, methane emissions were 2pc above their 1990 level.
Methane is a potent greenhouse gas. It is estimated to be 84 times more potent a warming agent than CO2 over a 20-year period, and 28 times more potent than CO2 over a 100-year period. In addition to its significant climate impacts, methane contributes to the formation of ground-level ozone, so there are health benefits from its reduction.
Methane has another important difference with CO2. For all practical purposes CO2 essentially stays in the atmosphere once it is emitted, but methane although a more powerful climate change agent disappears after around 10 years.
The rate at which global warming occurs is directly related to the amount of CO2 emitted. This is not the case for methane because of its short lifetime in the atmosphere. For methane, temperature change is a function of the rate at which methane emissions are changing, and not to the actual amount of methane emissions.
This means that if methane emissions are stable over time, they do not contribute to increased temperature. If methane emissions increase in a sustained manner, that increase has a very large impact on future temperature and much larger than a unit increase in CO2. Conversely, if methane emissions decrease in a sustained way, this will contribute to global cooling.
Methane emissions from Irish agriculture remained more or less stable over the period 1990-2017. This means that agricultural methane has not contributed to global warming over this period.