Allowing marginal hill country to revert to permanent native bush and the fast-tracked development of a vaccine to massively reduce methane emissions created by the digestive systems of cows and sheep emerge as two key recommendations from a new report by the Parliamentary Commissioner for the Environment.
"The biological emissions of 100 sheep could be offset indefinitely by about 6ha of marginal land left to regenerate into native forest," said the commissioner, Jan Wright, whose 100-page report concludes that impact of methane and nitrous oxide emissions from farm animals on climate change needs to be dealt with, even though agricultural emissions are excluded from the emissions trading scheme.
"For 100 beef cattle, about 28 hectares would be required and for 100 dairy cows, about 42ha," her report concludes, in addition to greater use of standing pads to collect cows' urine, especially during the wettest times of the year, to prevent nitrous oxide gas emissions and nitrate leaching into fresh water bodies.
"Allowing a million hectares of marginal hill country to revert to scrub could capture the equivalent of about 17% of all the biological methane and nitrous oxide currently emitted each year for 50 years," the report says. "This carbon store would continue to grow for hundreds of years."
About 1.6 million hectares of New Zealand is covered in plantation forestry, mainly pine, and "a further million hectares in pines could capture the equivalent of about 81% of all the biological methane and nitrous oxide currently emitted each year." Pine plantations would capture much more carbon because pine grows far faster than native forests.
Dr Wright also recommends that investment in scientific efforts to find a methane vaccine "would be so valuable that the research aimed at developing it should be ramped up as much as possible," even though she gives no timeframe within which such a discovery might be available.
A faster potential fix, albeit with less potential impact, would be to develop 'bolus' pills to be fed to cows and sheep that would inhibit their production of methane.
Their effectiveness would depend greatly on how often they had to be administered and whether animals' guts would become resistant to the compounds reducing methane production.
While a vaccine capable of reducing methane emissions by 25% of more would be a highly effective method of reducing methane emissions, "there are no successful trials of a methane vaccine as yet.
"Even a very optimistic scenario would not see inhibitors tailored for New Zealand becoming available before the 2020s. The development of a vaccine would take longer, if it can be done at all."
The report reveals that the Ministry of Primary Industries has, however, made "some progress" in pursuing a fast-tracked authorisation of DCD, the nitrogen inhibitor that was found in samples of Fonterra's milk powder in 2012, sparking a food safety scare despite its absence of impact on human health. DCD and melamine – a compound added illegally to milk by Chinese milk producers in 2008 leading to kidney damage in thousands of babies – share a basic chemical building block, meaning DCD was effectively lost to the New Zealand dairy industry as a nitrogen-inhibiting technology because there were no global standards for its presence in food.
Agricultural greenhouse gas emissions have been left out of the ETS partly because technologies to reduce emissions are too scarce and New Zealand is unusual among developed countries for having around half its emissions come from animals rather than carbon dioxide from burning fossil fuels.
However, both methane and nitrous oxide remained damaging greenhouse gases, despite methane's short life compared to CO2.
"The ETS is not the only mechanism that can be used" to control them, Wright said.
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