New climate change legislation for NI could be based on a system that compares different greenhouse gases and which more accurately reflects the warming effect of methane, MLAs have been told.
“It is important to emphasise that methane is a relatively short-lived gas within our atmosphere. It has a lifetime of 12.4 years and compares to other [greenhouse] gases which can have lifetimes of thousands of years,” said NI Assembly researcher Mark Allen.
Speaking at a Stormont committee last week, Allen said that agriculture is responsible for 77% of total methane emissions in NI, with most of this coming from ruminant livestock.
MLAs were told that GWP100, the system of comparing different greenhouse gases which is most widely used at present, does not accurately account for the short atmospheric lifespan of methane.
However, there is growing interest in new emission metrics such as GWP* as it considers methane’s different global warming effect when compared to other greenhouse gases.
“With the GWP* metric, it does envisage that if you cut emissions of methane, you will see cooling. It doesn’t give you a basis to increase methane emissions. But if you stood still, [it shows] a lot of the warming from methane emissions has already happened,” Allen said.
MLAs were told that the Intergovernmental Panel on Climate Change (IPCC), the body which advises governments on climate policy, does not recommend any particular system for comparing different greenhouse gases.
Allen quoted from a recent IPPC report which states that “it is ultimately a matter for policymakers to decide which emission metric is most applicable to their needs”.
The NI Assembly researcher also said it is accepted by scientists that different sources of methane having different warming effects in the atmosphere.
“Methane from fossil fuel burning has slightly higher emission metric values than those from biogenic sources (such as emissions from ruminant livestock), largely due to the release of carbon dioxide when you burn oil or gas,” Allen said.