OPINION: The latest report by the Intergovernmental Panel on Climate Change confirms that agriculture is a significant source of greenhouse gas emissions.
No group will therefore be more surprised than farmers, when they hear how much they are doing "right" to minimise greenhouse gas emissions.
Agriculture has long had the finger pointed at it for being the biggest source of emissions in New Zealand.
However, few people - including perhaps farmers themselves - appreciate that the financially driven need to farm more efficiently has also had a positive impact on greenhouse gas emissions.
The increasing efficiency and productivity means that the total greenhouse gas emissions per unit of agricultural product (that is, per kilogram of meat or milk solids) have declined and are about 20 per cent less today than in 1990.
However, the story does not end there. New Zealand agriculture may be more efficient than ever, but it also produces more food than ever - particularly in the dairy sector, where milk solids production has nearly tripled since 1990.
Overall, greenhouse gas emissions from agriculture in New Zealand have increased by 12 per cent between 1990 and 2011. Without the improved efficiency, agriculture's total emissions would now be 30 per cent greater than in 1990.
Whether these contrasting trends in New Zealand's agricultural emissions cause concern or celebration depends very much on the role one sees for our country in addressing global climate change.
New Zealand trades on its clean and green credentials and has set a country target of reducing total emissions to 50 per cent below 1990 levels by 2050. Although this can be achieved by a combination of reduced absolute emissions, enhanced carbon sinks (for example, forests) and the purchase of credits for emission reductions in other countries, it is hard to see the target being met without absolute reductions in agricultural emissions.
On the other hand, as a major agricultural trading country, there may be little benefit in New Zealand curtailing its own production for the sake of reducing its emissions when the global population and demand for animal protein is rising.
Other countries - many of whom produce food less efficiently than New Zealand - would likely meet this demand, resulting in economic losses to New Zealand without gains to the global climate. Resolving this tension is inevitably a political process that can be informed, but not determined, by good science.
Meanwhile, what can farmers do? The answer is "be as efficient as you can". 

There is no indication yet that the historical improvements in production efficiency have reached a plateau.
In fact, greenhouse gas "footprinting" studies show us that individual farms vary considerably in their emissions per unit of product, highlighting the scope for improvement by less efficient farmers.
Optimising fertiliser use, utilising improved animal and plant genetics, improving animal fertility and longevity, and improved feeding practices will all help drive down emissions per unit of product.
"Best practice" needs to become "standard practice" across the sector.
Balancing climate change concerns with economic, social and environmental pressures will be an ongoing challenge for New Zealand farmers.
There are no easy answers. More intensive farm systems have the potential to deliver lower greenhouse gas emissions per unit of product - but come with the risk of greater nitrogen losses and increased absolute emissions.
In many catchments, limits to nitrogen leaching to protect our waterways constrain further intensification.
The key challenge for addressing greenhouse gases is that, even with continued improvements in efficiency, absolute emissions will continue to rise if the sector is to achieve its growth targets.
Additional options to reduce emissions are needed. Jointly funded by industry and government, researchers are working hard to provide such options - that is, practical solutions that will make a meaningful dent in emissions.
This is not pie-in-the-sky research. New Zealand researchers have already identified and bred sheep that emit less greenhouse gases than others, while being just as productive. Breeding for low emissions could, over time and by itself, reduce emissions by 10 per cent.
Science teams are also developing options for a vaccine or inhibitors to selectively suppress the generation of methane in the rumen. This approach would raise the prospect of also increasing productivity, given that every bubble of methane leaving an animal's mouth represents a loss of energy - energy that could have been used to support growth.
New Zealand's agriculture sector has proved itself to be incredibly innovative, which has allowed it to recover from the major shock of economic restructuring to become a world- leading performer.
The next step towards overcoming the challenge that climate change poses to agriculture and the New Zealand economy is to combine the innovation of our farmers with the savvy of our scientists.
By working together, New Zealand stands a much greater chance of meeting that challenge.
Harry Clark is the director of the New Zealand Agricultural Greenhouse Gas Research Centre, Mark Aspin is manager of the Pastoral Greenhouse Gas Research Consortium, and Andy Reisinger is deputy director of the New Zealand Agricultural Greenhouse Gas Research Centre.

- The Dominion Post
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