US President Joe Biden speaks during an event in the East Room of the White House on September 15 in Washington DC. Biden announced a new national security initiative in partnership with Australian Prime Minister Scott Morrison (L) and UK Prime Minister Boris Johnson (R). Photo: AFP

Australia will not back a pledge, led by the EU and the US, to cut methane emissions by 30 percent by 2030 due to concerns about the impact on farming, Prime Minister Scott Morrison said on Thursday.

However New Zealand, another major methane emitter through its dairy and sheep industries, may join two dozen other countries in signing the Global Methane Pledge.

"New Zealand is actively considering signing up to the pledge and will take a decision soon," a spokesperson for Climate Change Minister James Shaw said.

The US and EU announced the methane pledge in September, aiming to rally rapid climate action before the start of UN climate talks in Glasgow, which start on Sunday.

Methane emissions - which come from natural gas, open pit coal mines, and cattle and sheep - are the second-biggest cause of climate change behind carbon dioxide (CO2). They trap more heat than CO2 emissions but break down faster than CO2 in the atmosphere.

Australia this week adopted a target of net zero greenhouse gas emissions by 2050, after Morrison secured support from the rural-focused National Party, the junior partner in the ruling conservative coalition.

"What we've said very clearly, though, is we're not signing up to the 2030 methane request," Morrison told reporters in Canberra, denying the refusal was aimed at appeasing the Nationals. National Party leader Barnaby Joyce said separately a 30 percent reduction in methane emissions would spell disaster for the beef, feedlot, dairy and coal mining industries.

New Zealand support for the methane pledge would be a big step as the dairy industry accounts for around 20 percent of the country's exports.