Prime Minister John Key warned farmers yesterday that they rejected a response to climate change at their peril - endangering their reputations, future incomes and the economy at the hands of powerful global consumers.

He gave a hard-hitting speech yesterday in Wellington to the Federated Farmers' National Council.

"Our international reputation with our overseas consumers is at stake," he said.

"As a trading nation we simply cannot afford to get it wrong."

While the Government had some sway over access to overseas markets, it could not force consumers to buy New Zealand products if they did not think they measured up to their environmental standards.

"But we can help protect against that possibility. That's what we believe our emissions trading scheme does and I hope you will see it in that light."

Mr Key cited the recent ban by British supermarket Waitrose on fish that it deemed had been over-fished or harvested by irresponsible means.

It had banned New Zealand hoki.

The supermarket had not suffered and the move was considered a commercial success.

National, with concessions for Maori Party support, is taking through Parliament amendments to Labour's ETS which reduces the impact on the agriculture.

Mr Key told the meeting that officials had estimated that the annual cost of National's proposed emissions trading scheme on the average farmer would be $3000 by 2030 for agricultural methane and nitrous oxide emissions compared with $30,000 it would have been under Labour's scheme.

He said it was important to realise it would not be the ETS, or an international agreement on climate change or the United Nations, that damaged New Zealand's agricultural sector.

"It's our customers around the world ... who have the ultimate power to damage or enrich our farming sector and our economy.

"You can't afford for those people to turn your markets off - for three thousand bucks in 2030. It's not a gamble I would take with a $3 million farm."

Earlier yesterday, Federated Farmers' president Don Nicholson called on the Government to repeal Labour's emissions trading scheme and start afresh.

Mr Nicholson also suggested that farmers needed to revisit their previous opposition.

He said the ETS was a "shambles" and that National was "grasping desperately for solutions".

Its solution was to offer "privilege", referring to possible forest-sink deals being negotiated between the Crown and the Iwi Leadership Group.

"I've had a gutsful, an absolute gutsful, of having our efforts thrown back in our face."

Later he said that farmers were not getting "a free ride".

For the past 27 years that he had been farming "I have given everything to this country".

In only two of those years would he have earned considerably more than the average wage.

New Zealand farmers were world leaders.

"We just wish that in New Zealand they would be revered as that."