The latest international update on climate change says global warming is turning oceans acidic and threatening marine life but offers new hope - the cost of tackling carbon emissions is modest and the means to do it are already available.

The UN's Intergovernmental Panel on Climate Change yesterday delivered its strongest warning yet, calling the rise in global temperatures "unequivocal" and its effects potentially irreversible and laying blame - with at least 90 per cent probability - on humans.

But the report, which summarises the findings from three volumes of scientific research issued this year, said reducing greenhouse gas emissions was not overly costly and could be accomplished through "technologies that are either currently available or expected to be commercialised in coming decades".

Stabilising carbon dioxide levels by 2050 could be achieved at the cost of decreasing global GDP by up to 5.5 per cent - an annual slowing of 0.12 per cent - or it could even increase by 1 per cent.

The report, the result of five days of sometimes-tense negotiations among 140 national delegations, will be the basis of an attempt in Bali next month to force a new international agreement to follow the Kyoto Protocol, which expires in 2012.

Victoria University public policy professor Jonathan Boston said the report poured cold water on the idea - championed by parts of the business community - that tackling climate change would destroy the economy.

"It's very unfortunate that there aren't more leading New Zealand businessmen and women who recognise the long-term and the wider economic opportunities, rather than just narrow short-term self-interest," said Professor Boston, who is also deputy director of the Institute of Policy Studies.

"It's a bit of a luddite mentality, to be blunt. In the long run there's no question [reducing emissions] will make us better off, but potentially there could be long-term economic benefits as well."

The report is being trumpeted as an urgent call to action by green groups and organisations including Greenpeace, the United Nations and the European Union.

The report said climate change effects were already under way, worsening, and could be "abrupt" or "irreversible".

The effects of climate change were unavoidable, but adaptation and mitigation "can significantly reduce the risks".

Action - or inaction - in the next two to three decades would have a "large impact" on the chances of reducing emissions and stabilising the level of greenhouse gases in the atmosphere. Delaying action would see the window of opportunity narrow significantly while increasing "the risk of more severe climate change impacts".