Humanity’s burning of fossil fuels is postponing the next global ice age for at least 100,000 years, according to new research that has discovered the tipping point which plunges the planet into deep freezes.
Showing that human activity, via climate change, can alter global processes like ice ages is compelling evidence that the planet has entered a new geological epoch, dubbed the Anthropocene, according to the scientists.
Other recent research listed evidence from plastic pollution to the mass extinction of wildlife to show that the Earth has entered the Anthropocene.
The new research also shows that a major ice age was narrowly missed just before the industrial revolution, probably because the development of agriculture had nudged the amount of carbon dioxide in the atmosphere just above the tipping point.
“The bottom line is we are basically skipping a whole glacial cycle, which is unprecedented,” said Andrey Ganopolski, at the Potsdam Institute for Climate Impact Research (PIK) in Germany and who led the research. “It is mind-boggling that humankind is able to interfere with a mechanism that shaped the world as we know it.”
The cycle of ice ages created today’s landscapes and much of the world’s fertile soils.
The new research, published in the journal Nature, examined the eight global ice ages over the past 800,000 years and used complex climate models to determine the critical factors that kickstarted the big freezes.
The result was surprisingly simple. A particular combination of lower sunlight at a latitude of 65 deg N, where snow surviving through the summer leads to ice sheets, and low carbon dioxide in the atmosphere was the signal for a new ice age to dawn. The level of sunlight is very predictable as it varies with cyclical changes in the shape of the Earth’s orbit around the Sun and in the tilt of the Earth’s axis, called Milankovitch cycles.
But the level of CO2 has been drastically altered by human activity, rising from 280ppm at the start of the industrial revolution to 400ppm today. The researchers showed that even if carbon emissions are limited to the amount consistent with a 2C rise in temperatures - the internationally agreed goal - there will be enough CO2 in the atmosphere to avoid future ice ages that could have started 50,000 or 90,000 years from now.
“This is in principle good news, as ice ages are a great challenge,” said Prof John Schellnhuber, PIK director and part of the research team. Sea levels rise and fall by more than 100 metres during global ice ages, and runaway global warming could add another 70m to that.
“Like no other force on the planet, ice ages have shaped the global environment and thereby determined the development of human civilisation,” Schellnhuber said. “Now human interference is acting as a huge geological force, so this is a defining paper for the Anthropocene idea.” If carbon emissions are not restricted, he said, they could end the million-year-long period of ice age cycles altogether.
Michel Crucifix, at the Université catholique de Louvain in Belgium and not involved in the new research, said: “It reinforces previous assessments asserting that humanity’s collective footprint on Earth already extends beyond any imaginable future of our society.”
“Such long-term consequences may seem surprising, given that the emissions will occur over a few centuries at most,” he said. “In fact, the mean half-life of CO2 in the atmosphere is of the order of 35,000 years. Consequently, anthropogenic CO2 will still be in the atmosphere in 50,000 years’ time, and even 100,000 years, which is enough to prevent any glaciation.”
“The significance of the study is the definition of a tipping point for glaciation,” said Prof Tim Lenton, at the University of Exeter, UK, who was also not involved in the new study. “This elaborates the classical Milankovitch theory by adding the CO2 component.”
“It is convincing in showing the start of the next ice age will be delayed,” said Lenton. “But I was already expecting this result based on previous studies. What is interesting is how little anthropogenic CO2 is needed to prevent the next [ice age] – 500 gigatonnes of carbon – and we have already emitted that.”
Prof Eric Wolff, at the University of Cambridge, said the research goes much further than earlier work in quantifying the tipping point. “It conforms to what many of us would expect, but it’s always a big step forward when someone shows that one’s intuition is actually backed by solid calculations,” he said.
“Humans now effectively control the climate of the planet,” said Prof Andrew Watson, at the University of Exeter. “If only we were wise enough to be able to use that power responsibly. Unfortunately, I don’t think we’ve reached that level of wisdom yet.”