For about 10,000 years, our climate on Earth has been stable. Remarkably stable, in fact. Since the end of the last ice age, we humans have spent 400 generations taking advantage of this stability to build our civilisation.

We have had warm periods and little ice ages; but the changes have been small. We have always known pretty much when it will rain, what the temperature will be each summer and winter, and how high the rivers will flow.

This benign climate is arguably the main reason why our species has been able to progress. Why, within 400 generations, we have gone from the scattered tribes of spear-carriers and fire-raisers who emerged from their caves at the end of the ice age to become the first farmers, metallurgists, urbanists, industrialists and now the seven billion inhabitants of a digitised, globalised world.

Our massively complex society relies on the ability to plant crops knowing that they will grow, and build cities and infrastructure in places that won't be flooded by incoming tides or washed away by torrential rains.

Without these certainties, Homo sapiens would still be living in caves. When they fail even briefly – during Hurricane Katrina in New Orleans, say, or in Cumbria just last month – we know the consequences. What if these certainties failed more, or even most, of the time? We are more vulnerable than we think.

Global leaders need to think about this lack of certainty as they gather in Copenhagen to discuss what to do about climate change. For, as we fill the atmosphere with heat-trapping greenhouse gases, the blunt truth is that the good times are over. That era of climate stability is coming to an end.

In some ways, it is remarkable how far today's politicians have come in addressing what seems destined to be the defining global problem of the 21st century. Seventeen years ago, at the Earth summit in Rio de Janeiro, their predecessors signed the UN climate change convention that promised to prevent "dangerous climate change".

That led to the Kyoto protocol in 1997 – a rather feeble first step to fulfilling that promise. But now, in Copenhagen, they may finally agree on a definition of that term "dangerous", when they discuss halting global warming at 2C.

Many now realise that the fossil fuels which have powered our world through two centuries of unprecedented growth in both population and wealth have to be largely phased out within the next half century.

In the 17 years since the Rio meeting, scientists' understanding of what climate change could do to us has moved on too. At every step, the science becomes more worrying: our move away from a world of stable climate will not be gradual, it could be sudden and violent.

Runaway warming

The reassuringly smooth lines on the graphs produced by climate modellers may not, as the sceptics have argued, be how things turn out. The problem is that things may not be less dramatic than the models predict. They may instead be a great deal worse.

The talk now in the climate labs — in the tea rooms and, yes, in their private emails — is of tipping points and runaway warming. The fear is that beyond 2C or so, warming and rising sea levels may be impossible to halt. Even if we cut our emissions to zero.

The concerns are many. Some studies suggest that the acceleration of melting ice in Greenland and Antarctica could soon destabilise their great ice sheets — causing sea levels to rise by several metres over a few decades.

Other research shows that frozen methane (a potent greenhouse gas) may bubble up out of the melting Siberian permafrost in volumes that would raise global temperatures by several degrees. And that melting ice could interrupt the north Atlantic ocean circulation, which would alter global weather patterns and ultimately switch off the Asian monsoon season.-

Alarmist? Well, these are not firm predictions right now, just concerns. Racing tipsters among the scientists say the odds might be five-to-one or even ten-to-one against some of these potential disasters.

The often repeated question is: would you get into a plane if someone told you there was a ten-to-one chance it would crash?

Of course you wouldn't. So why take that chance with the planet?

And here is perhaps the most persuasive evidence that they are right to be worried. It's happened before. Nature has a track record on tipping points.

Before the long balmy era we have enjoyed over the past 10,000 years, climate was often much more tempestuous. The climate system does not generally do gradual change. It does big jumps based on tipping points.

Take events during the final few centuries of the last ice age. We now know that, as ice sheets collapsed, sea levels rose 20 metres – enough to drown much of eastern England — in less than 400 years. That is an average of 20 times faster than now.

The ice sheets collapsed because the climate warmed quickly. Around then, average temperatures in much of the northern hemisphere rose by around 10C within a decade. Researchers can measure that change in the bubbles of ice left behind in ice cores in Greenland.

Before that, temperatures had lurched in the other direction. Research published just last month shows that some 12,800 years ago, the world plunged into a thousand-year deep freeze in a single year, with average temperatures crashing by 16C.

Those were violent times. They could happen again.

Forces within our control

How did such changes come about? They were started by slow and subtle shifts in the orbit of the Earth that changed the amount and distribution of radiation reaching us from the sun. But this small effect was amplified by events on Earth — apparent tipping points in the climate system.

First, there were sudden movements of hundreds of billions of tonnes of carbon dioxide into and out of the atmosphere. During warming, the gas burped into the atmosphere from natural reservoirs, or "carbon sinks", such as permafrost and the oceans. And it rapidly left again during cooling.

Second, there were rapid changes in the ocean circulation system, switching the Gulf stream on and off. Exactly how the planetary wobbles and the carbon dioxide movements and the ocean changes fitted together is far from clear. But they did so to devastating effect.

And what is unnerving today is that the key element, the trigger for the sudden change, appears to have been carbon dioxide. The very gas we are busy pumping into the air at the rate of 30bn tonnes a year, mostly by burning fossil fuels.

Even nature would find hard to match that rate. Our carbon-based fuels — coal, oil and natural gas — are the fossilised remains of swamp vegetation, buried over hundreds of millions of years. Every year we burn what nature laid down over a million years.

So when sceptics tell me not to worry about climate change, I don't buy it. We are interfering with major geological forces. Carbon dioxide is the planet's thermostat. Nature has flicked the carbon switch before. Now we are flicking the switch again. We are interfering with the planet's life support systems.

And, whatever happens to nature, it is our own highly complex interconnected society, built on a lucky period of stable climate during a tiny sliver of planetary time, that looks most at risk.

That's the bad news. But here is the good news. It doesn't have to be like this. We are still in charge of our own destiny. We have the technology to end our dangerous dependence on carbon-based fuels. We can take our pick of alternative energy sources: wind and solar; geothermal; tides and waves; nuclear if we must. And we have the technology to use dramatically less energy, too.

Kicking the carbon habit need not be expensive — small change compared to the price of bailing out the banks. It would be a lot easier to arrange if we changed our lifestyles to ones based on quality of life rather than consumption, measured by a happiness index rather than GDP.

But the hair shirt is not the critical technology. And the real issue is whether we have the political will to make the change.

Lesson from history

The best news is that, like nature, our society itself has tipping points. And some of them are positive. Look at how we gave up smoking in bars and restaurants. Five years ago, I would not have believed it could happen so easily and painlessly.

Or how half a century ago, we banished the great smogs. After the Great Smog of 1952, which left around 10,000 dead, industrialists said two things. First: "It's only nature, we've always had smogs, what's the big deal?" And second: "Anyway, the problem is far too expensive to deal with."

That, albeit on a much bigger scale, is the task the world faces in Copenhagen. To cry "enough". To cross our own tipping point and decide to embrace a future carbon-free world.

Can we reach our tipping point before nature reaches one of its tipping points? That is, probably, unknowable right now.

But we should know a great deal more about our chances before the month is out.

Fred Pearce is author of The Last Generation: How nature will take her revenge for climate change (Eden Project Books) and writes a weekly greenwash column for environmenttheguardian.com