Methane's impact on warming misrepresented US scientist tells Red Meat Sector Conference

University of California Davis Professor Frank Mitloehner told farmers that methane is not carbon dioxide on steroids for planet warming, during a video link at the Red Meat Sector Conference in Christchurch. Photo / Tim Cronshaw

A United States scientist has told Kiwi farmers that methane's reputation as a super greenhouse gas pollutant is unfair and Californian farmers have proven methane emissions can be reduced.

University of California Davis Professor Frank Mitloehner said methane was a more potent greenhouse gas than carbon dioxide, but it was untrue that it was CO2 on steroids as it was a "different beast" with its impact on warming.

Carbon dioxide was the super pollutant and methane was the super opportunity to reduce warming as long as it was managed, he said.

Dr Mitloehner said there was no additional warming to the planet through methane emissions, as long as herd sizes were kept constant.

"I call methane the fast and furious greenhouse gas," he said.

"Furious because it has a good punch to it, 28 times more potent per molecule than CO2, but fast because it has a very short lifespan.

"In sharp contrast to other greenhouse gases, methane is not just produced, but is also destroyed."

He said emission sinks and atmospheric removal of methane from a molecule called a radical in about a decade were important when it comes to quantifying greenhouse gases and warming.

The same did not happen to carbon dioxide, which had a lifespan of 1000 years, or nitrous oxide, he said.

"In other words every time you ever burn fossil fuels which are oil, coal and gas and every time your parents, grandparents and grand-grandparents did, all that stuff is in the air - it will pretty much stay forever.

"But if your cattle belch, then the methane that goes [out] today will replace the methane that they belched a decade ago, and that means a constant source of methane does not have additional methane concentration in the atmosphere and that means no additional warming."

If methane was reduced then warming would be reduced, he said.

Mitloehner told 300 delegates on a video link at the Red Meat Sector Conference in Christchurch that Californian dairy operations had reduced greenhouse gases by two million metric tonnes - a 30 per cent reduction since 2015.

He said California was well on the way to achieving the goal of climate neutrality - no longer adding warming to the planet - by 2027, and its dairy could then sell carbon credits to other sectors.

"Here in California, we have a law that mandates 40 per cent reduction of methane by 2030.

"At first our farmers were very worried about this, but then they heard the state would financially support them [in] reducing methane, for example by covering lagoons."

Large manure storage ponds called lagoons had been covered to capture methane as biogas.

Rather than burning biogas for making power for the dairy or nearby communities, this is converted to go into a natural gas pipeline to deliver a less-polluting, renewable fuel for truck fleets.

"So the 40 per cent goal is out there, that's the law, and we started this business a couple of years ago and we are already at 30 per cent and that's without rules, regulations and fines.

"This is with a carrot approach rather than a cane approach of financially incentivising reductions of methane."

The United States cow herd has fallen to 9 million from 25 million in 1950, yet milk production has increased 60 per cent.

The carbon footprint of a glass of milk is two-thirds smaller than it was 70 years ago.

Mitloehner supports a new matrix called GWP Star to characterise short-lived greenhouse gases - instead of the existing GWP100, which compares methane with CO2 emission equivalents to work out the warming potential.

The problem was that GWP100 over-estimated methane's warming impact of herds by a factor of four, and overlooked its ability to induce cooling when methane emissions are reduced.

An Intergovernmental Panel on Climate Change report had since confirmed that simply expressing methane emissions as CO2 equivalents overstated its effect, he said.

"People like myself have identified that the issue of using this old matrix is starting to be problematic.

"It's a reasonable matrix when you have methane sources going up, but let's say cattle herds are constant or if they're falling and methane is being reduced, then the GWP100 has really strong limitations."

He said GWP Star looked at the impact of methane on climate over time, its rate of change and its short lifespan in the atmosphere.