Planting more trees to cut greenhouse gas emissions is only a short-term solution, says Massey professor of energy research Ralph Sims.

Billions more trees will need to be planted in order to hit New Zealand's net zero emissions target by 2050.

New government-commissioned research projects an additional 10 per cent of land may need to be reforested, according to Climate Change Minister James Shaw.

"In New Zealand we've often thought about action on climate change being a sunk cost," Shaw said. "But it may actually be our competitive advantage."

Critics worry the Government's Zero Carbon Bill – to be released for public consultation on Thursday – will leave the farming community feeling "besieged".

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And Massey professor of energy research Ralph Sims said agriculture had many opportunities for the future, but the path to zero emissions would be an "incredibly difficult" one. "Planting trees is only a short term option. Once you keep planting trees and end up with the entire country covered in trees, what do you do?"

DAVID UNWIN / STUFF Federated Farmers vice president Andrew Hoggard says technological innovation is needed to achieve zero emissions by 2050.

The legislation setting out the strategy for the 2050 net zero emissions target will be introduced to Parliament this year.

The Zero Carbon Act will establish an Independent Climate Change Commission (an interim one is in place) which will develop five-year rolling carbon budgets outlining how each sector of the economy will meet New Zealand's greenhouse gas reduction targets.

Sims said the only option to drastically reduce the country's greenhouse gas emissions was to move away from animal products.

"It's incredibly difficult but not impossible. It means we're going to have to make some major changes. For carbon dioxide we know we need to reduce oil and gas reserves. And for agricultural emissions we can hope science gives us some options to reduce the amount of methane, otherwise we have to move away from the industry.

"This target can absolutely kill industries."

ROSS GIBLIN/STUFF Climate change Minister James Shaw says climate change action is thought of in terms of cost, but it could prove to be New Zealand's competitive advantage..

National leader Simon Bridges said the target had caused anxiety amongst farmers .

"The farmers have had it hard, with David Parker's capping of cow numbers and pulling out of the irrigation fund. [Farmers] feel besieged," Bridges said.

"We need a thought-through phased plan that doesn't unduly disrupt our economy and our people."

Federated Farmers vice president Andrew Hoggard said farmers felt under attack with mycoplasma bovis and said the focus needed to be on reducing carbon emissions through transport use.

"It seems like every man and his dog is doing something on climate change. To reach the zero carbon target we're going to need to see technological innovations," Hoggard said.

"It's really going to come down to science."

DAVID UNWIN/STUFF National leader Simon Bridges says farmers feel "besieged".

But Shaw said the zero emissions target as part of the Paris Climate Change Agreement could make New Zealand a world leader in farming and agriculture.

He cited comments from French president Emmanuel Macron, whose nation has traditionally been at loggerheads with New Zealand on trade. Macron said he was keen for the European Union to negotiate a free trade deal with New Zealand, because of this country's environmental credentials.

"Although agriculture has been the hardest challenge to deal with when it comes to climate change in the past few decades, it's the area of greatest opportunity for us in the coming three decades.

"We already have this reputation of having highly productive, innovative and adaptive farming. As other countries look to come to net zero at some point, they can look to us."