Grieve's comments come as New Zealand Prime Minister Jacinda Ardern heads to the United Nations Climate Action Summit in New York. World leaders attending have been told to take action plans to cut their countries' greenhouse gas production rather than words.
Grieve has been investigating climate change research for a decade. In 2009 he set up the Pastural Farming Climate Research group to support and bring together scientific research on the topic. It now has 2000 members.
Grieve said most countries' carbon emissions came from CO2. The need to reduce levels of this particular greenhouse gas, rather than methane, was driving international moves to cut carbon emissions.
Methane targets 'not needed' in some countries
He said that, for some countries, managing methane emissions might include not needing prescribed reduction targets for this greenhouse gas.
New Zealand was one of these countries, in his opinion, as its grass-based livestock production system is among the most carbon neutral in the world.
Grieve said the Ministry for the Environment's (MfE) consultation document for New Zealand's current Climate Change Response (Zero Carbon) Amendment Bill debate stated this country's methane levels needed only to continue at current stabilised levels — rather than be reduced — to ensure domestic emissions of this greenhouse gas did not contribute to any further increase in global temperatures.
He said New Zealand's methane emission levels had not gone up for 10 years.
Grieve accepts in principle there is some degree of man-made contribution to climate change. But he did not see this contribution being as serious as was being put forward by some.
He said information from United Nations' Intergovernmental Panel on Climate Change highlighted that only a quarter of the one degree rise in world temperature since pre-industrial times was caused by humans.
Big move to highlight climate change
Grieve's comments come at the same time as an unprecedented international move where more than 250 global media organisations, with an audience of one billion across 32 countries, are this week all highlighting climate change leading up to the event.
Grieve said robust science must underpin any government-imposed carbon emissions mitigation costs communities might face.
"Prescribed climate change mitigation actions will cost. It's important to make sure arguments in support of specific actions are based on robust research and a good understanding of that research.
"Any costs borne by New Zealanders must be justifiable."
Grieve said quality science was particularly important when deciding where to set New Zealand's prescribed 2050 methane emission levels — these in turn influencing any costs potentially loaded onto primary animal-protein producers in particular.
The need for robust science and its understanding applied in New Zealand and around the world. One example of this was better understanding needed of the carbon footprint tool.
"If the UN is going to establish our (human) environmental impact, we need a better carbon footprint tool. Our current tool for this doesn't allow for a true comparison between activities, because not all carbon emissions are the same."
Grieve said imposing climate change mitigation costs on New Zealand's animal protein producers would impact production and create other carbon emission consequences.
Reduced local meat production could mean New Zealand would have to buy product from overseas.
This would add further cost and create its own carbon emissions.
New Zealand would need food for its growing population.
"We will always need to eat," he said.
Grieve has produced food for consumers in New Zealand and overseas for more than four decades. He was a dairy farmer for 30 years, eventually 50:50 sharemilking at Ruatangata before 12 years ago shifting to the 15-hectare Poroti avocado property he bought in 1997.
He said cows should not be demonised as part of the climate change mitigation debate.
"It's wrong to demonise ruminants (cows).
"The ruminant is a magnificent animal. Sunlight and CO2 produces grass in abundance across New Zealand that in turn allows for a low-cost production system where cows turn the grass into food.
"Methane cycles through that production system, staying at the same level overall in New Zealand, rather than increasing, for the last 10 years."
