Dr Rick Pridmore, chairman of the Pastoral Greenhouse Gas Research consortium, says the push for cleaner water will help drive lower emissions.

The Paris climate change agreement has been signed. What will it mean for New Zealand farmers and the primary sector? This Q&A clarifies some points.

Q: Are New Zealand farmers big producers of climate change emissions?

A: First of all the big picture: the world's population is too great and it's growing (7.3 billion today, projected to reach 10 billion by 2050). Until we get around to reducing our numbers, little will change. Secondly, 85 per cent of the world's problems are industrial emissions - too many cars and dirty factories.

DAVID UNWIN / FAIRFAX NZ A cow has its emissions recorded at Massey University's labs.

Q: OK, what part do our farmers play?

A: On a global scale, not much. New Zealand produces only 3 per cent of the world's milk, for example. But our cows, sheep, deer, goats and other ruminant livestock burp and fart methane. When other global warming gases are added, agriculture is responsible for 47 per cent of New Zealand's emissions. It's not a good look.

READ MORE: Agriculture must be pulled into climate-change equations

Q: Are any other countries' agricultural emissions as high as a proportion of their total emissions?

A: The only developed country which comes close to New Zealand is Ireland, with 32 per cent. But many developing countries are greater or on a par with New Zealand (Uruguay with 85 per cent emissions from livestock).

Q: Federated Farmers says New Zealand farmers are very efficient. Is that true?

A: Since 1990 the agricultural sector has made greenhouse gas efficiency gains of about 1 per cent a year. That means they are producing 1 per cent fewer greenhouse gas emissions to produce the same amount of meat, milk and wool.

Q: How have they done that?

A: Mainly through an intense focus on improving management and animal genetics.

Q: Even so, haven't the actual amount of emissions risen since 1990?

A: Yes, as more farms have converted to dairy, methane emissions have increased 10 per cent.

Q: What will force change on farmers?

A: There are several outside forces which will have a big impact in the next decade. The first is the nationwide push for cleaner freshwater. Dr Rick Pridmore, chairman of the Pastoral Greenhouse Gas Research consortium (PGGRC), says in some regions farmers will have to reduce nitrogen to curb pollution. This in turn will mean fewer nitrous oxide emissions. In Hinds, Canterbury, greenhouse gas emissions could be reduced by 30 per cent. Nationwide, the gains will be fewer, but significant.

Q: How soon will this happen?

A: By 2017, "good practice" should lower emissions by 7 per cent. As regulations kick in, there will be greater reductions after 2020.

Q: What else might happen?

A: Economic volatility. Dairy farmers especially have learned that milk prices may not go as high as they did two seasons ago. They have had to reduce livestock and inputs.

Q: Have they really? What about palm kernel imports?

A: Greenpeace has attacked Fonterra for contributing to rainforest destruction by feeding cows palm kernel expellar (PKE), a by-product of the palm oil industry. Pridmore says it's not a simple question. Cows fed on PKE produce less nitrogen and therefore fewer nitrous oxide emissions than if they are fed on grass. But if people buy the argument that demand for PKE fuels rainforest destruction, thereby boosting carbon dioxide emissions, then the dairy industry loses the argument.

Q: What other developments are in the wind?

A: Mark Aspin, manager of the PGGRC, predicts approaches currently being developed have the potential to give a further 1.5 per cent a year efficiency gains. These include breeding livestock for lower emissions, low greenhouse gas feeds, development of a methane vaccine and a drench to inhibit methane.

Q: What feeds are those?

A: Some brassicas (rape, swedes) are being bred which lower emissions, by as much as 30 per cent when fed as a full diet. The problem is that livestock do not live on brassicas 12 months a year, so nationally over a year the reduction might be less than 2 per cent.

Q: What about the vaccine and drench?

A: Both could inhibit methane. Pridmore prefers the vaccine because it uses antibodies already produced by the cow. Both it and the drench are at "proof of concept" stage, and could be ready for use in five to seven years. Both technologies are targeting about a 20 per cent cut in emissions.