The Government is to make law a planned 50% reduction in greenhouse gas emissions from 1990 levels by 2050.
Environment Minister Nick Smith announced the move on Saturday at the National Party's environment forum in Akaroa.
The Government proposes to gazette the reduction under the Climate Change Response Act 2002, thus passing it into law.
Dr Smith says it will only be achieved by substantial developments in technology.
"We believe a 50% reduction in greenhouse gas emissions from 1990 levels by 2050 is a realistic but credible target for New Zealand."
He says New Zealand will need to reduce net emissions by 31 million tonnes a year.
"This is a very big ask when nearly half our emissions come from agriculture and when we already produce 70% of our electricity from renewables.
"It will only be achievable with major technological innovations in areas like agriculture and transport, which are quite possible over this timeframe."
Councils get more time to cut pollution
The Government also announced what it calls a more realistic plan to reduce air pollution.
Dr Smith has described the previous Labour Government's pollution policy as dramatic and draconian.
He says it set an unrealistic deadline of 2013 for councils to comply with air pollution standards.
Dr Smith says councils will now have between three and seven years longer to meet the required standard.
"We're going to give moderately polluted areas like Auckland, Napier, until 2016 to reach the standard.
"For those higher polluted areas like Christchurch, Timaru, Rotorua ... Nelson, with over 10 current exceedances per year, we're going to require them to get down to three by 2016 and to meet the full compliance standard by 2020."
Dr Smith says the new policy will also be tougher on vehicle emissions and ban open fireplaces in new houses built in areas with poor air quality.
Sub-Antarctic marine reserves
Other announcements from the forum include more lenient air pollution targets, a large marine reserve around the Sub-Antarctic Islands, and a taskforce to encourage clean, green business.
Conservation Minister Kate Wilkinson says the Government is to set up three new marine reserves covering 435,163 hectares around New Zealand's southernmost outlying islands.
The protection will cover the sea around the Antipodes, Bounty and Campbell islands, which form part of the sub-Antarctic islands off the south-east coast.