The deal reached at global climate change talks in Copenhagen has disappointed politicians and scientists worldwide, while reaction has been mixed in New Zealand.

Prime Minister John Key has described the deal as "short of the aspirations and expectations" people held, while the Green Party's former co-leader Jeanette Fitzsimons has labelled it a "tragedy for humanity."

Labour Party climate change spokesman Charles Chauvel, who also attended the conference, said the deal could be built on.

The United Nations climate talks ended with a bare-minimum agreement that fell well short of the conference's original goals after prolonged negotiations failed to paper over differences between rich nations and the developing world.

Critics have complained the explicit deal struck to limit global warming to 2 degC provided no details of how this goal would be reached, and that the emission cuts that were promised would be insufficient to get there.

The New Zealand government had never expected a binding deal and Mr Key had originally not planned on attending, describing it as a photo opportunity. However, he did end up going.

Mr Key told reporters that he was comfortable with the text and New Zealand could meet it without changing its emissions' reduction targets.

New Zealand's climate change ambassador, Adrian Macey, described the deal as a "modest" step in the right direction.

Mr Chauvel said the outcome was not as good as it could have been.

"On the other hand, two weeks of discussion have made it abundantly clear what the obstacles to an agreement are, and what the position of the major players on each issue is."

He thought considerable progress had been made around verification of different countries' reductions and on help for developing countries to adapt.

"The momentum of this progress needs to be built on. At the same time, much more work is needed to set out binding and appropriate targets for both developed and developing countries."

New Zealand needed to do its part and set a more ambitious target, Mr Chauvel said.

New Zealand's conditional target for reducing climate harming emissions is to reach 10-20 percent below 1990 levels by 2020, and Mr Key says a stronger target would hurt the country's economy.

Ms Fitzsimons saw the deal as a failure "papered over with some fine-sounding words by [President Barack] Obama".

The purpose of the meeting was to agree on a second commitment period for the Kyoto protocol but that had not been achieved, she said.

"We came here wanting an ambitious, fair and binding agreement. The talks have failed on all three counts.

"There are no country targets, only an appendix where countries offer non-binding reductions which collectively will not stop warming of 2 degrees. As it is not ambitious or binding, it cannot be fair to the developing countries that are already suffering from climate change."

President Obama has defended the agreement as a breakthrough and for the first time the world's largest economies accepted their responsibility to act.

However, top climate scientists have criticised the agreement. Among them was Andrew Watson, a professor at the University of East Anglia in Britain, who said the agreement would not achieve its aim.

"This agreement will almost certainly not be sufficient to enable that target (2 degrees Celsius) to be met – legally-binding tough limits in place over the next few years would be needed for that," he told AFP.

The Nobel-winning UN science panel warned in a benchmark 2007 report that if average temperatures increased by more than 2.0 degC on pre-industrial levels, it could lead to runaway climate change and severe effects.