By Simon Hooper for CNN
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LONDON, England (CNN) -- The reality of climate change, and mankind's causal role in the process, are facts that are now almost universally accepted.
Yet while most people have read of the threat of rising sea levels and melting polar caps, or experienced a nagging guilt when booking a cheap flight or buying exotic fruit imported from the other side of the planet, hitherto global warming has largely been something we are happy to leave to the scientists to worry about.
In cooler, wetter parts of Europe it is still possible to joke about Mediterranean summers and olive groves in Scotland.
But a new book aims to dispel such complacency. "Six Degrees", by leading environmental campaigner Mark Lynas, sounds a red alert for the health of the planet, charting degree-by-degree the likely consequences of rising temperatures up to the worst-case scenario 5.8 degrees Celsius (10 degrees Fahrenheit) rise envisaged by the Intergovernmental Panel on Climate Change's 2001 report. Last month, the IPCC shifted that upper figure to 6.4C (12F).
Lynas insists he remains optimistic that climate change need not spell utter devastation, but the central message is unequivocally bleak.
"I'm not saying that the human race is imminently doomed but it's also clear that the clock is ticking and time is running out in order to take action to avoid the escalating damages which could make the whole process unstoppable," he told CNN.
Lynas' predictions, an aggregate of hundreds of scientific papers, make shocking reading. Calling Hurricane Katrina "a portal into the future," he says it is already too late to avert a rise of up to one degree that will lead to Arctic meltdown, extreme drought across much of the world and the destruction of low-lying island nations such as Tuavalu and the Maldives.
The pace of change is already breathtaking. Between 2004 and 2005, 14 percent of the Arctic Ocean's perennial ice disappeared - some 720,000 square kilometers (447,000 square miles) -- a depletion Lynas calls "instantaneous" in geological terms.
"If you have ever wondered what it will feel like when the Earth crosses a tipping point, savour the moment," he writes ominously.
But it is further ahead, as temperatures rise towards two degrees, that the true destructive consequences of climate change are unleashed. Extreme European summers would cause hundreds of thousands of deaths due to heat stress while rising sea levels would devastate vulnerable coastal areas and cities including New York, London, Shanghai and Bombay.
A three-degree rise would mean the death of the Amazon rainforest -- the equivalent of cutting off mankind's oxygen supply during an asthma attack, says Lynas.
By that stage, he warns, runaway global warming would have become an unstoppable "deadly game of dominoes", ultimately leading to further rises that, based on studies of previous cases of similar climate change in the earth's paleontological history, would spell the near-certain extinction of almost all life on the planet.
Perhaps the most alarming aspect of "Six Degrees" is the tight constraints in both time and temperature within which mankind must act to avoid such apocalyptic nightmares.
With admirable precision, Lynas says we have eight years to cap global carbon consumption at current levels, and then a further 35 years (until 2050) to cut emissions by 90 percent to stand a good chance of keeping global warming within a couple of degrees of current temperatures this century.
Still, he warns, he rates the chances of avoiding runaway global warming as no more than 50-50.
"If we had wanted to destroy as much of life on earth as possible, there would have been no better way of doing it that to dig up and burn as much fossil hydrocarbon as we possibly could," he writes.
With climate change now making regular front page headlines and high-profile figures such as Al Gore -- whose global warming documentary "An Inconvenient Truth" recently won an Oscar -- Arnold Schwarzenegger and Tony Blair pushing the issue ever higher up the political agenda, Lynas says there has been a sea change in attitudes.
But he warns recognizing the problem is only the start of tackling the looming crisis.
"There has clearly been a sociological tipping point in terms of the levels of awareness that people have and the commitment that people are beginning to feel for dealing with the problem," he says.
"That's clearly reflected in the amount of time and energy politicians are now giving to moving themselves into this new green landscape. But that doesn't mean we should underestimate the extent to which denial remains a strong undercurrent."
For Lynas, action means switching to a globalized low carbon economy with individual carbon allowances and a tradable emissions market as soon as possible.
Even so, he warns, current political targets for stabilizing the amount of carbon dioxide in the atmosphere -- such as Britain's target to cut emissions by 60 percent by 2050 - fall a long way short of those he believes necessary to keep climate change in check.
"The climate budget will become as important as the financial budget because it's going to define just as much, if not more, how people live their lives than whether there's a penny gone on tax or 3p on a bottle of wine," he told CNN.
"Sixty percent by the middle of the century is not enough in my opinion but it's sufficiently drastic to force a transition to a low carbon economy."