UN Secretary-General Ban Ki-moon has thrown his weight behind a massive report on climate change, warning that current trends in carbon emissions will lead to disaster.

In the crowning summary of a landmark review, the Intergovernmental Panel on Climate Change (IPCC) said emissions of three key greenhouse gases were at their highest in more than 800,000 years.

'Human influence on the climate system is clear, and clearly growing,' Ban said at a press conference marking the final chapter in a major report by the Intergovernmental Panel on Climate Change (IPCC).

'I am really adding my political voice to what scientists have been working very, very hard (on),' he said.

The report said earth is now on a trajectory for at least 4C warming by 2100 over pre-industrial times - a recipe for worsening drought, flood, rising seas and species extinctions.

'The scientific case for prioritising action on climate change is clearer than ever,' IPCC chief Rajendra Pachauri said.

'We have little time before the window of opportunity to stay within 2C of warming closes. To keep a good chance of staying below 2C, and at manageable costs, our emissions should drop by 40 to 70 per cent globally between 2010 and 2050, falling to zero or below by 2100.'

The report - the first overview by the Nobel-winning organisation since 2007 - comes ahead of talks in Lima next month to pave the way to a 2015 global pact in Paris to limit warming to 2C.

But the negotiations have been hung up for years over which countries should shoulder the cost for reducing carbon emissions, which derive mainly from oil, gas and coal - the backbone of the world's energy supply today.

READ MORE: Rifts remain at UN talks on climate pact

The report said switching to cleaner sources, increasing energy efficiency and carrying out other emission-mitigating measures would be far cheaper than the cost of climate damage.

The bill today for doing this is affordable, but delay would cause it to rise substantially for future generations.

'Mitigation cost estimates vary, but... global economic growth would not be strongly affected,' the IPCC said, estimating that 'ambitious' carbon curbs would shave 0.06 percentage points annually from global consumption this century, which is targeted to grow by 1.6-3.0 per cent annually.

'Compared to the imminent risk of irreversible climate change impacts, the risks of mitigation are manageable' said Youba Sokona, one of the lead authors of the new report.

The document painted a bleak tableau of a world affected by a 4C increase, marked by hunger, homelessness, species loss and violent conflict over scarce resources.

There would be a 'very high risk of severe, widespread and irreversible impacts globally,' it said.

World talks have been troubled for years over which countries must shoulder the burden for reducing greenhouse-gas emissions - the heat-trapping fossil-fuel gases driving global warming.

After years of preparation, the negotiations are heading for a climax in Paris in December 2015, where the hope is to seal a global pact that will take effect from 2020.

READ MORE: World urged to act at UN climate summit

An important stepping stone in the process will be a new round taking place in Lima from December 1-12.
- See more at: http://www.skynews.com.au/news/top-stories/2014/11/03/ki-moon-throws-weight-behind-climate-report.html#sthash.x2tfECQ7.dpuf