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The current system used to account for the global warming contribution of different greenhouse gases is not well suited to accounting for methane’s contribution to climate change, especially methane derived from ruminants, Teagasc director Prof Frank O’Mara has said.
Methane has a short half-life and does not stay in the atmosphere as long as CO2 does, meaning that its contribution to global warming may be overestimated when emissions are stable, O’Mara told an Animal Taskforce webinar last week.
Animal Taskforce is a public-private partnership between research bodies, farming organisations and the wider agri-food sector across Europe.
Second-largest contributor
“Methane is the second-largest contributor to global warming after CO2 so far. It is responsible for about 30% of the increase in global temperatures that we have seen to date,” stated O’Mara to attendees.
“The metric that is often used to look at global warming - GWP100 - is not a good metric to assess [methane’s] contribution, however, because of its short half-life.
“And methane, unlike CO2, it does degrade in the atmosphere. It has a half-life of about 10 years and this does impact on the way we should look at methane.”
Key distinction
O’Mara said that this creates a “very important distinction between the two gases” that should be accounted for in emissions reduction plans.
He explained that if methane emissions are stabilised, its contribution to global warming “rises slowly until it reaches equilibrium and, thereafter, the temperature impact of methane is more or less constant”.
“This is very different to what happens with CO2 if we manage to stabilise emissions. The temperature continues to increase even with stable CO2 emissions.”
Currently, the EU bundles all greenhouse gases together for emissions accounting purposes and requires the net warming associated with all of these to reach net zero under the GWP100 system.
Importing energy
O’Mara stated that around 60% methane emissions originate from human sources, with energy generation and waste also contributors to methane emissions.
It was heard from the Teagasc director that farming makes up a larger portion of the EU’s methane emissions than is seen in other regions of the world, as the EU imports a substantial share of its energy needs, the emissions associated with which are accounted for in the exporting regions.
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