Most of us know three or four generations of our families: us, our parents, our grandparents, and maybe some great grandparents too. Of course, we humans go back thousands of generations since we evolved from apes. But most of what we have done to create our modern world has happened over about 400 generations – since the end of the last ice age, when ice caps retreated from Europe, Asia and North America and humans first began farming.
Since then, the world’s climate has been remarkably stable. We have had warm periods and little ice ages, but the changes have been relatively small. Our ancestors 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.
That stable climate may be the main reason we went from being scattered tribes of spear-carriers living in caves to become the first farmers, the first city dwellers, the first industrialists and now the 7 billion inhabitants of a digitized, globalized world.
Our massively complex society sometimes makes it seem as though we don’t need nature at all. But actually, we still rely on planting crops that we know will grow because the temperature will be right and the rains will come. And we rely on the fact that our cities won’t be flooded by rising tides or washed away by torrential rains. If we didn’t have this certainty, we wouldn’t just lose the fruits of our labours, we might not even labour in the first place. Crops wouldn’t be planted, and cities wouldn’t be built. What’s more, with so many of us living in big urban agglomerations, and so much of the planet’s surface under cultivation, there aren’t many places we could go to find safety and food security if our systems were to break down under the strain of an unpredictable climate.
Of course disasters do happen, including climate disasters like droughts and floods and hurricanes. But for now, they are rare enough for us to be able to pick up the pieces and carry on.
Now comes the scary bit, however. It looks like this era of climate stability – of knowing what the seasons and the rains will do – is coming to an end. Climate disasters may become much more frequent and more intense. The reason, of course, is man-made climate change.
We know from basic physics that the gases we put into the air when we burn fuels like coal and oil heat up the atmosphere. That’s old news. What is new, and even more worrying, is that scientists are seeing more and more evidence that the warming won’t come gradually. It may come suddenly.
And it won’t just be warming: there will be big and fast changes in weather patterns. So hurricanes may start appearing in places where they have not been seen before, like Brazil or Australia. Desert conditions could spread from the African Sahara into Europe. The annual monsoon rains that irrigate crops for 3 billion people in Asia might fail. Rivers may rise up and flood whole cities while storm surges from the oceans inundate low-lying coastal areas.
Evidence from the past
These are not yet firm predictions. But according to many scientists, our weather is about to get much more dangerous and unpredictable. Perhaps the most persuasive evidence that they are right is that it’s happened before. Go back more than 10,000 years and it looks like nature has a track record of doing climate change not gradually but in sudden leaps.
Take events during the final few centuries of the last ice age, just over 10,000 years ago. Around then, average temperatures in much of the northern hemisphere rose by around 10ºC within a decade. That’s like going from permanent winter to permanent summer within 10 years. Researchers can measure that change in the bubbles of air left behind in ice cores in Greenland.
The warming caused huge ice sheets on land to collapse into the oceans, and sea levels rose round the world by 20 metres in less than 400 years. That is an average of 20 times faster than now, and enough to flood most coastal areas of the world.
Not long before that, temperatures had lurched in the other direction. Research published just last year shows that around 13,000 years ago, the world took just one year to plunge into a thousand-year deep freeze, with average temperatures crashing by 16ºC. Humans retreated into their caves and kept the fires going.
Those were violent times. They could happen again. What is unnerving today is that the key element in those changes, the trigger for the sudden shifts back then, appears to have been carbon dioxide. The very gas we are busy pumping into the air when we burn coal and oil. Carbon dioxide is the planet’s thermostat. Nature has flicked the carbon switch before. Now we humans are flicking it ourselves. That’s scary.
Here are some troubling thoughts. Some scientists are warning that the Amazon rainforest could die by the middle of this century as a result of global warming. The region will be too hot and too dry for the trees to survive. Trees are also made of carbon. If that happens, the trees would release their carbon into the air. Giving an extra boost to warming.
Another gas that can warm the planet is methane. Nature has lots of methane stored out of harm’s way, in odd hiding places round the planet. Methane is frozen inside the ice of the Arctic, and buried under the seabed. If it escapes to the atmosphere it will add to warming.
There are signs that methane releases from the oceans warmed the world in the distant past. And it looks as if current global warming is starting to release methane from thawing soils in Siberia and Alaska. Scientists have measured it bubbling up into the air. Right now the bubbles are small. But as the world warms they could become bigger.
The worry is that we are starting a runaway reaction, in which we add carbon dioxide and methane to the atmosphere, causing warming that releases more carbon dioxide and methane, causing more warming.
That’s the bad news. But here is the good news. None of this is yet inevitable. We humans are still in charge of our own destiny. We have the technology to end our dangerous dependence on carbon fuels like coal and oil. We can take our pick of alternative energy sources: wind and solar; tides and waves; even nuclear power maybe.
It is a big challenge for our species. We have had it easy for 400 generations. We have taken nature and the climate for granted. But we can’t do that any longer.Fred Pearce