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".
Among the report's findings was that the acidity of the ocean's surface water - which absorbs carbon dioxide from the atmosphere - has risen 30 per cent and this could treble by the end of the century.
Other impacts include shrinking glaciers - six cubic kilometres of ice melted away from New Zealand glaciers in the past 30 years - thinning Arctic summer sea ice and thawing permafrost.
By 2100, global average surface temperatures could rise by between 1.1C and 6.4C compared to 1980-99 levels, pushing up sea levels by 18cm to 59cm. Heatwaves, rainstorms and tropical cyclones are expected to become more frequent, more widespread or more intense.
In New Zealand, more frequent and intense storms and coastal flooding are expected by 2050, and an increase in coastal developments would make the problem worse.
In eastern regions, water security problems and agriculture and forestry production are projected to decline because of increased drought and fire by 2030 - but this would be offset by initial gains in agriculture from a slightly warmer climate and consistent rainfall.
Every country would feel the effects, but those at the forefront would be developing countries and small island states where hundreds of millions of people live in low-lying areas or rely on a stable climate.
Climate Change Minister David Parker said the report showed it would be more costly to ignore climate change than to deal with it. "Even at the household level, simple steps can cut vehicle fuel and energy bills significantly and improve people's health while cutting emissions."
He said Government announcements to tackle climate change - including an emissions trading scheme - looked at making use of IPCC-approved measures, including putting a price on carbon and developing renewable energy.
UN Secretary-General Ban Ki-moon appealed to political leaders for a breakthrough at a climate change conference in Bali next month.
"We cannot afford to leave Bali" without one."
THE IPCC REPORT:
* Climate change is unequivocal, and its effects are well under way and becoming worse.
* The most severe effects would leave the world's poorest nations the most vulnerable and threaten plant and animal species with extinction. In New Zealand, drought would hit the agriculture and forestry industries, while storms and rising seas would batter coastal developments.
* The cost of cutting emissions to a stable level by 2050 is small. It could decrease annual global GDP growth by 0.12 per cent, or could even increase global GDP growth.By Derek Cheng Email Derek