A previously held theory about the cause of global ice ages could be wrong, at least according to new research done by an international team of scientists.

Current theory believes that ice ages occur when radiation from the sun increases and creates a wobble in Earth's orbit around it, causing the continental ice sheets to expand and contract.

However, this theory only applies to the Northern Hemisphere's ice sheets, and if true, the Earth's wobble should create effects that are directly opposite in the Southern Hemisphere.

New research refutes that theory and suggests at least the last ice age was the same all over the world at the same time.

"Records of past climatic changes are the only reason scientists are able to predict how the world will change in the future due to warming," says lead author Alice Doughty, a glacial geologist at Dartmouth College. "The more we understand about the cause of large climatic changes and how the cooling or warming signals travel around the world, the better we can predict and adapt to future changes."

Researchers mapped out ridges of rocks left over after large glaciers moved in New Zealand: these glaciers were larger in the past. They dated the rocks, as well as other similar rocks throughout the world. Their research showed that the glaciers of New Zealand were large around the same time that ice sheets covered both Scandinavia and Canada. This occurred during Earth's last ice age about 20,000 years ago. On top of that, previous research shows that glaciers in Chile were also large at the same time.

This suggests that the last ice age affected both the northern and southern hemispheres of the planet at the same time, conflicting with the original theory about what causes ice ages.

So, if the Earth's wobbling orbit didn't cause the last ice age, what did? After dating the New Zealand rock ridges, researchers realized that their ages put their origin at around the time sea surface temperatures were cooler there. So, it's likely that ocean temperature played a part in the last great ice age.

"Our results point to the importance of feedbacks — a reaction within the climate system that can amplify the initial climate change, such as cool temperatures leading to larger ice sheets, which reflect more sunlight, which cools the planet further," says Doughty. "The more we know about the magnitude and rates of these changes and the better we can explain these connections, the more robust climate models can be in predicting future change."