Australian scientist Tim Flannery said the world still had "one to two decades" to take action to reduce global warming, despite one of Britain's best-known environmentalists warning that the world has already passed the point of no return on global warming.
In what The Independent described as the bleakest assessment yet of the effects of climate change by a leading scientist, Professor James Lovelock said billions would die by the end of the century, and civilisation as we know it would be unlikely to survive.
But Dr Flannery believes there is still time to turn the situation around.
"We have set change in motion and that change will take about 100 to 200 years to wash its way through the system - even if we stopped greenhouse gas emissions tomorrow," said Dr Flannery, who is director of the South Australian Museum and author of climate book The Weather Makers.
"I don't think we've yet reached that point where we are tipping the world's climate into a new regime.
"We've got maybe one to two decades to address the issue."
Dr Flannery's comments are based on his own studies and he is now reviewing Professor Lovelock's research.
But he warned that there had already been significant changes to the world's climate.
"We've already raised the temperature of the planet by between 0.6 or 0.7 of a degree," he said.
"That's had a large impact in terms of rainfall patterns worldwide, breeding patterns of species, [their] migration and distribution, and of course it initiated the melting of the north polar icecaps."
And if this global warming continues, Dr Flannery has equally catastrophic predictions for humanity.
"Once we get to two degrees of warming, we will initiate change that human civilisation, as we now know it, can't survive," he said.
"Sea levels will rise too rapidly for us to adjust and it's likely that extreme weather events will become so widespread and severe that our infrastructure won't survive and changes in rainfall and ocean circulation will bring about a collapse in world food production."
Professor Lovelock, who in the 1970s coined the Gaia thesis that the Earth is a single organism, called on governments to start making preparations for a "hell of a climate" in which, by 2100, Europe and southern Australia would be 8 degrees hotter than they are today.
"The few breeding pairs of people that survive will be in the Arctic, where the climate remains tolerable," Professor Lovelock wrote in The Independent.
The scientist makes his predictions in a new book, The Revenge of Gaia, which argues that the feedback mechanisms that used to keep the Earth cooler than it would otherwise be are now working to amplify warming caused by human CO2 emissions. "
Sadly I cannot see the United States or the economies of China and India cutting back in time and they are the main source of CO2 emissions."
Professor Lovelock is a controversial but respected scientist who gave a briefing on global warming in 1989 to the then prime minister, Margaret Thatcher. Two years ago he caused a furore in the environment movement by urging greens to embrace nuclear power to reduce global warming gases.