Earth's 100,000-year Ice Age Cycle Explained

Although scientists know that the Earth undergoes an ice age every 100,000 years, the mechanisms behind this phenomenon have not always been entirely clear.

A new study published in the journal Nature, however, offers a new theory that, according to its authors, points to the alternating influence of continental ice sheets and climate on this global climatic interchange.

"If an entire continent is covered in a layer of ice that is 2,000 to 3,000 meters thick, the topography is completely different," Heinz Blatter, an emeritus professor of physical climatology at ETH Zurich, said regarding this feedback effect. "This and the different albedo of glacial ice compared to ice-free earth lead to considerable changes in the surface temperature and the air circulation in the atmosphere."

Furthermore, the researchers found that large-scale glaciation alters the sea level and thus ocean currents -- both of which play a role the climate.

In coming to these conclusions the scientists relied on computer models combining ice-sheet simulation with a pre-existing climate model. They were then able to calculate the glaciation of the northern hemisphere for the last 400,000 years.

Besides accounting for variables such as ground topography and the physical flow properties of glacial ice, the model factored in these climate and feedback effects as well.

As a result, the researchers were performing the first simulation of the entire northern hemisphere of its kind and, in doing so, were able to determine why ice ages begin slowly and end quickly.

The answer, they found, lies in the observation that the growth or shrinkage of an ice sheet is not only determined by surface temperature and precipitation but, due to the aforementioned feedback effects, its size as well.

"The larger the ice sheet, the colder the climate has to be to preserve it," Blatter explained.