A new international study casts doubt on the leading theory of what causes ice ages around the world -- changes in the way the Earth orbits the sun.
The researchers found that glacier movement in the Southern Hemisphere is influenced primarily by sea surface temperature and atmospheric carbon dioxide rather than changes in the Earth's orbit, which are thought to drive the advance and retreat of ice sheets in the Northern Hemisphere.
The study raises questions about the Milankovitch theory of climate, which says the expansion and contraction of Northern Hemisphere continental ice sheets are influenced by cyclic fluctuations in solar radiation intensity due to wobbles in the Earth's orbit; those orbital fluctuations should have an opposite effect on Southern Hemisphere glaciers.
"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. 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," says lead author Alice Doughty, a glacial geologist at Dartmouth College who studies New Zealand mountain glaciers to understand what causes large-scale global climatic change such as ice ages. "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. 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."