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New Zealand's methane

problem and its

false representation

Monday 14th May 2018

Les Jones

One of the recommendations from the Productivity Commission’s recently released draft paper, The Low-Emissions Economy, was the “two-basket” approach to accounting for methane. This approach characterises methane as a short-lived gas (it breaks down over about ten years), in comparison to CO2 which lasts for centuries, and is accumulating in the atmosphere in an alarming manner. Therefore, the two-basket approach suggests that New Zealand puts most of its effort into reducing CO2 and worry about Methane later.

This is a misguided and dangerous approach and represents another in the long line of fudges which New Zealand has foisted on the world in order that we be perceived as doing something to curb greenhouse gas emissions, when in fact our net emissions have risen more than almost any developed country since 1990.

There are three problems with Methane:

Firstly, if it is a short-lived gas, why has the concentration of it in the atmosphere risen by 160% since pre-industrial times, but the concentration of CO2 in the atmosphere has only risen 45% over the same period. The answer is that when 1 kg of methane breaks down into CO2 and water, it is being replaced by more than 1 kg of new methane. Now the rate of new methane in the atmosphere has varied over time: from 2000 to 2007, the rise had levelled off to the extent that some thought we could soon stop worrying about methane as a greenhouse gas. Unfortunately, since 2013 methane emissions have spiked, and scientists are desperately seeking the cause of this. New Zealand, by downplaying the importance of Methane’s warming effect, is basing its response on outdated numbers, and crossing its fingers in the hope that methane’s rise will ease off again. If it doesn’t, then we will have to completely reset our priorities.

The second problem with Methane is that New Zealand produces a lot of it. Methane, according to the latest inventory, makes up 43% of our emissions, with CO2 at 44% and Nitrous oxide at 12%. These proportions are different from nearly every other OECD country; in Australia, for example, methane only makes up 12 % of emissions, with CO2 about 85%. One can see the attraction for NZ agriculture, which produces nearly all of the methane (CH4) and Nitrous oxide (N2O), in de-emphasising these gases, so that the onus for reducing New Zealand’s emission falls on transport and energy, not farmers. This situation is doubly attractive when there are known ways to reduce energy and transport emissions (e.g. renewables or EV’s), but few options for reducing livestock emissions apart from reducing stock numbers. Thus, if NZ adopted the “two-basket approach”, it would be appearing to be, but not actually playing its part in the global effort to reducing emissions.

The third problem with CH4 lies in the measurement of how strong a greenhouse gas it is. Internationally, the UN gives CH4 a Global Warming Potential of 28, which means that it is 28 times stronger an atmospheric warming agent than CO2 (which has a GWP of 1). This is measured over 100 years, but if we measure its effect over 20 years, then it is much more powerful at 86 times CO2. Let me explain: 1 kg of CH4 is emitted, but in 10 years it breaks down. That means that for the remaining 90 of the hundred years, to all intents and purposes it doesn’t exist and, therefore, can’t do any warming. That means that it has done its hundred years of warming in the first 10 years, hence its GWP10 of 86.

Well, the difficulty for NZ is that our government is probably proposing a Climate-Change target of zero net emissions by 2050, which by the time they get around to it will be only 30 years away. It is dishonest to use GWP100, when our timeframe for action is only 30 years. Surely, we need to use GWP30, which is 79 times CO2. For most countries it won’t make that much difference but because CH4 is 43% of our emissions, using GWP30 would change the face of our profile. Our gross emissions would leap from 78.7Mtns to 139.4Mtns, and our per person emissions skyrocket from 16.7 Tonnes per person (about 5th in the world) to 29.6 (highest in the world) Lets investigate some further ramifications of this: Agriculture’s share of NZ emissions would rise from 48% to 75% and that would mean that Agriculture would shoulder the vast majority of the responsibility for reducing NZ emissions.

There is one positive in all this: if we radically reduced our CH4 emissions, our contribution to reducing the world concentration of CH4 would be immediate, because it is a short-lived gas.


Given the uncertainty in the near-future rate of increase in world methane emissions, it would be irresponsible of New Zealand to develop an emissions-reduction pathway based on the notion that Methane, because it is only short-lived, should not be a priority in efforts to do our fair share towards limiting global warming to 2 degrees above pre-industrial levels. Runaway rises in Methane levels have been implicated in the earth’s past great extinction events. Methane trapped in the arctic, if it melts, would cause a tipping point in world temperature increase. At the moment, Methane contributes about 15% of global warming. Don’t mess with methane!

More analysis of New Zealand's

Methane problem 

Submission on the Zero Carbon Bill. The crux of the problem is how do you measure methane against CO2 in order to decide how much to reduce each one betwenn now and 2050.

The spreadsheet tracking NZ's methane from 19900 to 2050 in real terms is here

The Zero Carbon Bill and Methane: recognising the problem.

Scenario 1 - NZ methane emissions over 100 years. This spreadsheet models our methane emissions from 1990 to 2017 then forward to 2050 assuming constant levels from now on

Scenario 2- NZ methane from 1990 to 2050. Spreadsheet assuming annual 3% reduction in both methane and CO2

The complete spreadsheet for NZ methane and CO2 emissions 1959 to 2050

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