DairyNZ proposed that the 2050 methane reduction target be set at up to 24 per cent, with regular reviews against "robust criteria." That position was supported by Fonterra and its Shareholders' Council, Miraka, Synlait and Tatua.
"This will be a real challenge for our sector, but we are up for it. While there are things we can do now on-farm, much of the reduction in emissions will be reliant on technological advances in feed, breeding or other interventions," Dr Mackle said.
"A lot is being asked of our farmers across a variety of issues, such as water quality and biosecurity. If a methane target is set based on a global reduction scenario, rather than what is sensible at home, then they will simply disengage.
"This isn't an academic exercise. There will be real implications and real costs, for real people. At the end of the day, most farmers are small business owners doing their best."
DairyNZ estimated that a reduction in methane of up to 50 per cent could reduce dairy farmers' total profit by 33 to 42 per cent over the 20 years to 2050, more than 10 times the cost of $2500 per farm, estimated in the government's analysis. The impact for rural communities and the wider economy could be huge.
"We can't afford to lose sight of the fact that New Zealand is responsible for less than 0.2 per cent of total global emissions, and dairy farmers are among the most emissions-efficient producers in the world," he added.
"While there may well be some benefits to leading the world on climate policy, this could constrain our ability to lead the world in other areas, most notably the efficient production of high-quality, low-emissions milk.
"Our biggest contribution to global agricultural emissions reductions will be to show what is possible both on-farm and with new technologies, once they become available. This highlights the importance of continued investment in scientific research and development that will help us reduce agricultural emissions.
"DairyNZ knows how important it is for us to move on climate change, but we also know the importance of moving at a pace that doesn't leave farmers, families and communities behind."