Science says option two best fit for zero carbon bill

With consultation on the government’s zero carbon bill now closed, the agriculture sector waits with baited breath to see how intensive its role will be in the national quest toward significant emissions reductions by the year 2050.

Three options were presented to the public for consultation and feedback:

  • One: reduce carbon dioxide emissions to net zero by 2050, but not other gasses like methane or nitrous oxide

  • Two: reduce carbon dioxide levels to net zero levels by 2050 and stabilise emissions of short-lived gasses like methane at either current or reduced levels

  • Three: reduce emissions of all greenhouse gasses to net-zero by 2050

Dairy NZ and Federated Farmers both sided with option two, a logical choice when reviewing the science, according to Andrew Hoggard:

“Well we’ve gone for option two in our submission. A lot of the science now is backing up the fact that methane just needs to be stabilised, it’s the long-lived gasses, CO2, nitrous oxide, they are the ones that need to be controlled. So that’s the point we’re arguing. You’ve got to be realistic around which options are available.”

 The science Hoggard refers to can be found in an article put together by professor of geosystem science Myles Allen and Victoria University climate change professors Dave Frame and Adrian Henry Macey, which echoes the popularly held view that current approaches to emissions reductions are fundamentally flawed.

They provide a simple graph displaying the difference between flow and stock pollutants over time, which shows that with stock pollutants (like CO2), concentrations of the pollutant accumulate as emissions continue. The flow pollutant decays, while the stock pollutant remains in the environment.

However, currently, the powers that be treat stock and flow pollutants as being equivalent and therefore interchangeable.

As Allen, Frame and Macey explain, “this is a mistake, because if people make trade-offs between emissions reductions such that they allow stock pollutants to grow while reducing flow pollutants, they will ultimately leave a warmer world behind in the long term.”

“Instead”, they say, “we should develop policies that address methane and other flow pollutants in line with their effects…which for countries with high methane emissions, for example from agriculture, can make a huge difference to how their emissions are judged.”

New Zealand is one of these countries.

The fact that “agriculture makes up 50% of New Zealand’s total emissions” has oft been repeated in the past few months and is consistently brought up in debates about the need to include agriculture in the ETS.

However, the statement needs to be supplemented with the scientific facts presented, not just by these three, but also the likes of science and policy research associate on climate pollutants at Oxford, Dr. Michelle Cain, which show a need to identify and quantify the more negligible impacts flow pollutants, like those released by agriculture, have on global warming.

In a paper entitled, “A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation”, Cain, Frame, Allen, Macey and several other climate and atmospheric scientists proffer that:

“The conventional approach to assessing whether a medium-term emissions trajectory is consistent with a long-term temperature goal, simply by comparing it with a set of available scenarios, is opaque at best, and at worst misleading.”

The approach they refer to treats all greenhouse gasses as CO2-equivalent using a metric known as ‘global warming potential’, or ‘GWP’.

As Cain explains in her own article on the subject, the current method of converting non-C02 emissions to C02 emissions is multiplying the gas (say methane) by its global warming potential over 100 years (GWP100). The latest IPCC report placed the GWP100 for methane at 28, meaning 1Gt of methane is equated to 28 Gt of CO2.

The issue with this Is that it “masks the fact that 1 Gt of methane has a strong warming influence when it is first emitted, which then diminishes rapidly over a few decades”, and by comparison, “a 28Gt equivalent emission of CO2 would effectively persist in the atmosphere for centuries or longer, continuing to cause warming at almost the same rate as when it was first released.”

If all greenhouse gas emissions, including those from agriculture, are taxed, countries like ours will be unfairly penalised under this system, assuming the aim is to penalise contributions to warming.

Cain illuminates this fact using an example that compares cows to closed power stations:

“Consider a power station and a herd of cows. A power station emits CO2 by burning fossil fuels. This CO2 is taxed. When it shuts down permanently, it emits no more CO2, so is no longer taxed. However, the CO2 already emitted continues to affect the climate for hundreds, or potentially, thousands of years. So even after closing down, that power station still contributes to holding up global temperatures because of the CO2 that remains in the atmosphere.

“Now to the cows. A herd of cows emits methane, so the farmer is taxed for those emissions. If the herd remains the same size with the same methane emissions every year, it will maintain the same amount of additional methane in the atmosphere year on year. In terms of its contribution to warming, this is equivalent to the closed power station.

“The power station pushed up global temperatures when it was running in the past, just as the farmer’s great-grandparent pushed up global temperatures when they were building up the herd of cattle. But neither a steady herd of cattle nor a defunct power station is pushing up global temperatures any more.

“However, under almost all proposed systems for taxing emissions that attempt to include methane, the farmer would get taxed for their herd’s methane emissions every year the cows were alive, while the owner of the closed power station would not.”

Cain hypothesises that the best way to rectify this would be to use GWP to calculate equivalent emissions, as this equates changes in methane emission rates with tonnes of CO2. Thus, a stable emission of methane equates to a zero rate of CO2 emissions under GWP, as it does not change the level of warming into the future and would, therefore, not be taxed.

Returning to Allen, Frame and Macey, this method reflects what they feel is the best way to move forward: employing polices that assist sectoral fairness within countries, e.g. in a country like ours, recognising the different roles of stock and flow pollutants to give farmers a “more reasonable way to control their emissions and reduce their impact on the environment, while still acknowledging the primacy of carbon dioxide emissions in the climate change problem.”

They conclude that: “An ideal approach would be a policy that aimed for zero emissions of stock pollutants such as carbon dioxide and low but stable (or gently declining) emissions of flow pollutants such as methane”- in other words, option two for New Zealand.

The question now, is whether the science has been evaluated and considered by those determining the outcome of the zero-carbon bill, an outcome Andrew Hoggard hopes will prevent serious damage to the sector:

“We don’t want to penalise NZ farmers and discourage production here in NZ, just because agriculture makes up 50% of emissions doesn’t mean our Ag sector is bad, it’s a thing of context”.

The bill will be introduced in October and entered into force in April of next year.