Rod Carr argues gas may be dirtier than coal – could he be right?

Sunday, 16 February 2025

NZ’s big four power companies are discussing jointly supporting a ‘strategic fuel reserve’ at the Huntly power station that would in the first instance, at least, comprise coal.

ANALYSIS: Fossil fuels all emit carbon dioxide and, among them, coal has become the dirtiest word for climate change activists.

So an announcement on Wednesday that the country’s big four power firms were working to keep the Huntly power station’s coal-fired turbines spinning for several more years might seem a hammer blow for the environment.

But during a flurry of exit interviews in December, the now former climate change commissioner Rod Carr lobbed a bombshell.

New and emerging research suggested that burning gas was actually worse from an emissions perspective than generating the same amount of energy from burning coal, he asserted.

The reason that coal has been regarded as the dirtiest of fuels it is that it is pretty much pure carbon, so all of it turns to carbon dioxide when combusted.

Not so natural gas, which is mostly made up methane.

It contains both carbon and hydrogen atoms and when it combusts it releases a mix of carbon dioxide and water, with the hydrogen-to-water component of that reaction a form of ‘green’ energy.

For that reason, it is commonly stated that coal creates about 1.8 times more emissions than gas when burnt to create electricity.

Climate Change Commissioner Rod Carr warns government choices have consequences.

But Carr argued that taking “whole-of-life” greenhouse gas emissions from fossil gas and coal, gas was worse.

The case against gas

The idea that coal is almost twice as 'dirty' as fossil gas is only true if you only consider emissions at the point of combustion, Carr said.

'It is not true if you count all the emissions from finding the gas, cleaning the gas, distributing the gas, storing the gas and the incomplete combustion of the fossil gas.

“Because at every point in that chain what leaks is methane, which we know is a highly potent greenhouse gas.”

The emerging research Carr points to is a study published by Cornell University professor Robert Howarth last year.

Methane disappears from the atmosphere much faster than carbon dioxide, but Howarth’s research claimed that burning gas was about a third worse for global warming than burning coal, 20 years after it was combusted.

About 100 years after combustion the impact was about equal, he estimated, after which the equation could flip.

Only about 35% of the total emissions from gas came from the carbon dioxide that was released when it was actually combusted, his study reported, with the bulk coming from methane and other emissions further up the chain.

Carr acknowledges that study focused on the emissions profile of liquified natural gas (LNG) produced in the US and exported to Europe and not gas that was, say, piped straight from a deep sea well to a power station.

A fair chunk of the emissions Howarth totted up from gas — at least 13% of the total — came from the energy and methane lost in converting natural gas to LNG and emissions from its shipment.

His study also assumed most gas would be extracted from shale, which is a relatively emissions-intensive process, and that coal wouldn’t be shipped as far as LNG.

In the case of New Zealand neither would hold true, as gas here is produced from conventional wells and most of our power-station coal is imported from Indonesia.

“Emissions from Maui gas burnt at Huntly depend on leakage at the time of extraction, compression, piping and burning,” Carr observes.

“Those emissions may be relatively lower than life-cycle emissions from burning imported LNG.”

The Cornell University research centred on the emissions profile of LNG exported from the United States.

But old plant and pipelines have higher emissions due to the technology and age of the equipment, he also says, adding in another wild card.

Energy Resources Aotearoa ‘flabbergasted’

John Carnegie, chief executive of Energy Resources Aotearoa, which primarily represents the interests of businesses involved in the oil and gas industry, says he is “flabbergasted” by Carr’s claim.

It highlights the risk of taking “a specific, narrowly-defined study and applying it to the general case, resulting in a serious loss of objectivity and perspective,” he says.

Australian Energy Producers, the peak body for the Australian energy sector, commissioned a review of Howarth’s paper.

That review found that the methodology significantly overestimated natural gas production and processing emissions, Carnegie says.

“We also note that fugitive methane emissions from coal mining are not accounted for. This undermines the statement that coal is less polluting than LNG because the basis for comparison differs.”

A verdict

While perhaps no-one could know for sure without a complex New Zealand-specific study, Energy Resources Aotearoa seems to have a strong point that Howarth’s findings are not readily transferable to New Zealand.

Domestically produced gas would appear likely to have a lower whole-of-life emissions profile than LNG produced from shale gas in the US and exported to Europe, and therefore coal – at least taking the ‘100 year’ perspective.

It is probably also worth noting that gas-fired turbines can be switched on and off much more quickly than coal-fired turbines, which take several hours to reach peak output.

What remains in question is whether NZ can have just a small gas industry providing back-up fuel for power firms.

So there is less chance of unnecessarily emitting carbon when instead using gas to meet short term morning and evening peaks in electricity demand, for example.

Here, at least, the conventional wisdom that coal is “worse” than gas could hold true.

The grounds for an appeal

But there is another possible complication.

Coal is easy to store and it is possible to import only the amount that’s needed to fill in for hydro-electricity during a ‘dry winter’, for example.

But if New Zealand’s quasi gas industry regulator, the Gas Industry Company, is to be believed, it may be pretty difficult to have a small-scale domestic gas industry that is also viable.

A report it commissioned from Ernst & Young last year suggested that in order to support upstream investment in gas supply and keep gas wells open, it is necessary to have other large gas users such as methanol producer Methanex consuming gas — and ready to cut production and release gas to electricity generators when needed.

As the need for fossil-fuelled energy generation falls and becomes more short-term and erratic, as everyone hopes, it could be less emissions-intensive to rely more on an easily-storable solid fuel – even if that was coal – to make up the remaining gap, if the only alternative really was to maintain a large upstream gas industry to do the same job.

Carbon accounting nirvana

Using neither coal nor gas would be better.

Genesis Energy announced on Tuesday that it was hoping to source 300,000 tonnes of “torrefied biomass” a year from 2028 from Australian-owned company Foresta to replace at least some of the coal it burns at its Huntly power station.

That is a product similar to charcoal, that like coal is largely carbon.

But as it is made from non-fossilised wood, its carbon is counted by climate scientists and accountants as part of the atmospheric carbon cycle – releasing carbon dioxide that when burnt is cancelled out by the growth of new trees.

Energy Minister Simon Watts described Genesis’ biomass announcement as “a good signal and a sign of other opportunities in this market”, and the fuel also seems to find favour with Carr.

“If you captured the flue gas at the point of combustion of that biomass and re-injected those gasses into a functioning geothermal field where a power station was already doing gas capture and re-injection, you would have an energy-positive carbon sink, and in the central North Island, we have all the components to make that real,” Carr says.