Ice ages have shaped the global environment and human evolution. A recent study indicates humans are changing these natural cycles: Our CO2 emissions are likely to postpone the next ice age. What does this mean?
Ice ages occur cyclically over the Earth's history. But a recent study in "Nature" shows human-caused climate change will postpone the next ice age. DW talked to the lead author of the study.
DW: What determines whether and when a new ice age will occur?
Andrey Ganopolski: According to astronomic theory, a new ice age should occur when the earth's orbit takes it far away from the sun, and summer is colder than usual in the northern hemisphere, at high latitudes in Canada and northern Europe. These are the areas where big ice sheets can grow. Naturally, without any human influence, we would expect the new ice age to start 50,000 years from now.
But CO2 emissions affect the development of such ice sheets. Relatively large anthropogenic greenhouse gas emissions - say, two to three times what we have already emitted - would, according to our model, additionally postpone the next ice age so that it would only start 100,000 years from now. So we would completely skip one glacial cycle - which has never happened in the last 3 million years.
What would this mean for the long-term development of the planet?
Regular glacial cycles over the last 3 million years were extremely important, because most of the evolution of humans occurred during the last 3 million years. We are probably the product of glacial cycles, because it was probably the right conditions to increase our brainpower, because we had to be clever to survive in such a variable climate.
For the future, it is hard to say what such a long interglacial will mean for nature. Of course, for humans it is better to live in an interglacial than a new ice age.
So why should we be concerned about this?
Around 30 years ago, some scientists proposed we were very close to a new ice age. And sometimes this is used by climate skeptics to justify burning fossil fuels. Our study shows this argument is irrelevant. The ice age is not coming, anyhow.
Secondly, this shows we can affect the climate for up to 100,000 years, and that's surprising to many people. They think if we stop using fossil fuels tomorrow or the day after, everything will be fine. But that's not true. The carbon dioxide will stay in the atmosphere for an extremely long time. That means we are affecting Earth's future on a geological time scale.
So are we living in the "Anthropocene," i.e. an era in which not nature but humankind is determining the shape of the world we live in now and for centuries to come?
Yes. I like the idea of introducing the "Anthropocene" as a new geological epoch. Because if you compare our current climate and rate of change to what previously happened over many millions of years, this is unprecedented. It is a substantial deviation from the natural course.
Our paper illustrates that if you continue to emit a substantial amount of carbon dioxide, the Anthropocene will last for hundreds of thousands of years before systems return to anything like "normal" conditions. So the earlier we stop using fossil fuels, the smaller the deviation will be from this natural state, and the earlier systems will recover.
Some people might say why worry about such a long time scale, and since the CO2 is already in the atmosphere, it doesn't matter what we do any more. How would you respond?
That is not true. It does matter what we do. Our paper was also about the future of the Greenland and Antarctic ice sheets. And what we show is that even with the CO2 concentration we have already, we can expect that a substantial fraction of these ice sheets will melt. So obviously, in this respect, any further increase of CO2 will have even more negative effects. If we add more carbon to the atmosphere, it will stay there for an even longer time, and consequences will be much more serious.
I fully agree that a time scale of 50,000 years is not something of practical importance to most people. It just illustrates that our impact on climate will last for a very long time - much longer than most people think. Basically, it will affect all generations, and if we care about them, we should stop using fossil fuels as soon as possible.
Andrey Ganopolski is a physicist and earth systems modeler with the Potsdam Institute for Climate Impact Research.
The interview was conducted by Irene Quaile.