"We accept that there is man-made climate change," he said.
"We accept that we should take some action and pull our weight, but we need to be very careful about it."
The reduction of greenhouse gas emissions would happen workplace by workplace, car by car, sheep by sheep, he said.
People had a right to know what the rules were before the country irrevocably committed to the protocol.
But asked what National would do if New Zealand had ratified by the time his party came to power, Mr English said: "It would only be in extreme circumstances that we would withdraw New Zealand from an agreement it had undertaken, so we need to think through how you get some sensible policy."
Finance Minister Michael Cullen had told the conference earlier that the Government's preferred policy package would be released on April 7, but Mr English said two or three years was a more realistic timeframe.
Alan Haronga, of the Federation of Maori Authorities, said his members saw Kyoto as part of a continual erosion of their rights under the Treaty of Waitangi.
"The goal of ratifying Kyoto moves the business risk we face from 'high' to 'extreme' and that is not acceptable to us."
Andrew Little, general secretary of the Engineering, Printing and Manufacturing Union, was concerned about the risk to jobs and said a case could be made for exempting much of the manufacturing sector, including cement, aluminium, steel and pulp-and-paper plants.
Federated Farmers president Alistair Polson said New Zealand should delay ratification.
"We need to know all the facts on inventory [how much methane gas is produced by different kinds of livestock and soils] and on the options for mitigating emissions."
He doubted that research into the diet of sheep and cattle would yield an easy solution soon.
Chris Baker, who chairs the Climate Change Pan Industry Group, called for a delay "to do the analysis and come up with smart policies".
He endorsed US President George W. Bush's policy announced last week - to reduce energy consumption relative to GDP, to invest in technology and fund it through robust growth.
Peter Whitehouse, of Business New Zealand, said that in sensitive sectors such as cement, steel and pulp and paper, which had thin margins, even the suggestion that they could face added costs might cause owners to shift production overseas.
Last year's power crisis had already damaged perceptions of the New Zealand business environment. "This cannot be allowed to escalate," Mr Whitehouse said.
Auckland University climate scientist Dr Chris de Freitas said summaries produced for policymakers by the United Nations Intergovernmental Panel on Climate Change were not balanced interpretations of the science in the panel's detailed assessment.
And evidence from climate models did not tally with data from satellites, he said.
Dr Robert Watson, the panel chairman, said the summaries were written by the scientists who wrote the big reports and they were extensively peer-reviewed.
Every Government had signed off on them, and 17 National Academies of Science had endorsed the panel's processes and conclusions.
nzherald.co.nz/climate
Intergovernmental Panel on Climate Change (IPCC)
United Nations Environment Program
World Meteorological Organisation
Framework Convention on Climate Change
Executive summary: Climate change impacts on NZ
IPCC Summary: Climate Change 2001
