Farm scientists at a new multi-million-dollar research facility believe they can cut the carbon footprint of milk by 20 per cent - even without using the latest emerging technologies.

Estimates show a model farm in the Waikato should be able to slash emissions per litre of milk without using the most cutting edge methods, such as those being developed to breed low-methane farm animals and cut nitrous oxide from effluent.

The 200ha, 800-cow farm, 8km south of Te Awamutu, is aiming for a greenhouse gas footprint of 740g of CO2 equivalents per litre of milk, compared with 900g for the average New Zealand dairy farm.

The savings would be made by upping production per cow and per hectare and cutting the use of nitrogen fertiliser. Any savings from emerging technologies such as nitrification inhibitors would be on top of that.

AgResearch opened the Tokanui farm on Friday after a $6.5 million conversion. AgResearch scientist Dr Stewart Ledgard said emissions would be measured after a year and compared to a benchmark established at the start of the project.

Methane and nitrous oxide, the major farm gases, are converted to CO2 equivalents and added to actual CO2 produced - for example any coal burnt to make electricity for farm milking machines - to work out the total carbon footprint.

The farm's launch came as Prime Minister John Key told farmers he had the support of the United States, Japan, India and China for a New Zealand-led Global Alliance to find ways to cut greenhouse gases from agriculture.

About half New Zealand's greenhouse emissions are from agriculture. Their treatment will be a key focus for New Zealand negotiators at the upcoming Copenhagen climate conference.

Farmers would like to be left out of New Zealand's mechanism for cutting greenhouse gases - the Emissions Trading Scheme - but Mr Key and Environment Minister Nick Smith made it clear last week that that was not an option. They told farmers agriculture made up a much larger proportion of greenhouse gases here than in Australia, which has decided to leave farmers out.

Climate Change Negotiations Minister Tim Groser has been arguing in the lead-up to Copenhagen that New Zealand is almost uniquely badly placed among Kyoto signatories because - unlike the myriad of alternatives to, say, coal-fired energy - there is as yet no technical fix for methane from livestock.

Negotiators will also be trying to make sure Kyoto rules deeming all carbon from trees to be released into the atmosphere as soon as the trees are cut down (even if the wood is used for timber or furniture) do not carry on into the next agreement.

If they are, New Zealand risks a bigger carbon bill in the 2020s, when large swathes of forest are due to be harvested.

The Government has set a greenhouse gas emissions reduction target of between 10 per cent and 20 per cent below 1990 levels by 2020, depending on whether developing countries agree to limit emissions.

Mr Smith, Mr Groser and climate change ambassador Adrian Macey will present those targets when they and a team of officials head to Denmark for the conference from December 7 to 18.

The negotiations were meant to decide what would happen after the first commitment period of the Kyoto Protocol, under which 189 countries agreed to reduce emission an average of 5.2 per cent below 1990 levels by 2012. But there is now widespread pessimism that a binding "Copenhagen Protocol" will be signed there.

When: December 7 to 18.
Where: Bella Centre, Copenhagen.
What: Negotiations to make a treaty to cut greenhouse gases to limit the chance of dangerous climate changes from 2012.
Who: Could be considered a success if it binds the top ten emitters who are responsible for two-thirds of the world's CO2 emissions. Unlike Kyoto, it's likely to include the US (the world's biggest emitter), China (the soon-to-be biggest emitter) and Australia (the biggest emitter-per-capita) plus more than 100 others.
Issues: Developed countries have not agreed how much they will give developing countries to help them limit emissions and adapt to climate change, nor which countries will get the most support.
Must include: A commitment by developed countries to reduce emissions and an agreement by developing countries to limit growth of theirs, then reduce them.

(source: International Institute for Environment and Development).
Some groups that often negotiate as a bloc include:
G77/China: A group of developing countries that want rich countries to take responsibility for their historical emissions.
Alliance of Small Island States: A coalition of 43 islands and low-lying countries concerned about rising sea levels.
African group: 50 countries which work together to highlight their relative poverty and vulnerability to climate change.
European Union: the 27 member states.
Umbrella Group: the non-EU industrialised countries, including New Zealand, Australia, the United States, Canada and Russia.