London, Nov 13 : Based on a new climate model, scientists have determined that had humans not radically altered the atmosphere by pumping massive amounts of carbon dioxide into it, the future might have seen a super ice age lasting millions of years.
According to a report in New Scientist, Thomas Crowley of the University of Edinburgh, UK, and William Hyde of the University of Toronto in Canada developed the climate model.
CO2 levels have slowly fallen from around 100 to 50 million years ago, possibly due to the rise of the Himalayas.
As a result, Earth has gradually cooled, with permanent ice sheets starting to form in Antarctica around 30 million years ago and later in the Arctic.
Then, 2.5 million years ago, the climate entered a curious new phase: it started oscillating wildly, see-sawing between interglacial periods with conditions similar to today's and ice ages during which the amount of permanent ice in the northern hemisphere expanded hugely.
At the peaks of these transient ice ages, much of northern Europe, northern Asia and North America were covered in ice sheets up to 4 kilometers thick, and sea levels were 120 meters lower than today.
From a "deep time" perspective, this ice age-interglacial cycle may be just another brief transitional phase. It has been becoming ever more variable, according to Crowley.
When the cycle began, the climate went from ice age to interglacial and back roughly every 41,000 years. More recently, it has been happening every 100,000 years.
The temperature swings have also become greater: the interglacials have been no warmer, but the ice ages have become much colder.
So, the overall cooling trend was continuing, until the arrival of the Anthropocene, the period in which humans have affected Earth's geology.
According to a simple climate model developed by Crowley and Hyde, this increasing variability was a sign that the climate was about to flip into a new stable state - a semi-permanent ice age.
"This ice age might well have lasted for tens of millions of years or more," Crowley said.
The model indicates that humans have pumped so much carbon dioxide into the atmosphere in little more than a century that levels are higher now than they have been for at least 800,000 years.
This will have delayed any switch to a long-lasting ice age indefinitely.
"We are probably very comfortably away from it happening now," Crowley said.