Eric Hopton for redOrbit.com – Your Universe Online

What causes the earth to freeze up and enter global ice ages?

Until now, a commonly accepted explanation is the Milankovitch ‘wobbly earth’ theory of climate in which changes in the way the Earth orbits the sun result in the creation of ice ages. The Milankovitch proposition is that 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. This theory, however, has just gotten served! It’s been challenged by in-depth research of the Southern Hemisphere’s mid-latitude glaciers.



It’s not the planetary wobbles, according to the researchers. Glacier movement in the Southern Hemisphere, they claim, is influenced primarily by sea surface temperature and atmospheric carbon dioxide rather than changes in the Earth’s orbit. If the Milankovitch theory was correct, those orbital fluctuations should have an opposite effect on Southern Hemisphere glaciers. But the findings of the research, which can be found in the journal Geology, refute that proposition.

[STORY: Ice age cycles realized using novel method]

The team used detailed mapping and beryllium-10 surface exposure dating of ice-age moraines (rocks deposited when glaciers move) in New Zealand’s Southern Alps, where the glaciers were much bigger in the past. The dating method measures beryllium-10, a nuclide produced in rocks when they are struck by cosmic rays. The researchers identified at least seven episodes of maximum glacier expansion during the last ice age, and they also dated the ages of four sequential moraine ridges.

Cold at the same time

The results showed that New Zealand glaciers were large at the same time that large ice sheets covered Scandinavia and Canada during the last ice age about 20,000 years ago. This makes sense in that the whole world was cold at the same time, but the Milankovitch theory should have opposite effects for the Northern and Southern Hemispheres, and thus cannot explain the synchronous advance of glaciers around the globe. This latest conclusion is supported by previous studies which proved that Chilean glaciers in the southern Andes also have been large at the same time as Northern Hemisphere ice sheets.

The ages of the four New Zealand ridges, which were respectively about 35, 27, 20, and 18 thousand years old, were found to align with times of cooler sea surface temperatures off the coast of New Zealand based on offshore marine sediment cores. The timing of the Northern Hemisphere’s ice ages and large ice sheets is still paced by how Earth orbits the Sun, but how the cooling and warming signals are transferred around the world has not been fully explained, although the team believe that ocean currents play a significant role.

[STORY: Where penguins hid during the last ice age]

“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,” said lead author Alice Doughty, a glacial geologist at Dartmouth College.

—–

Follow redOrbit on Twitter, Facebook, Google+, Instagram and Pinterest.

Comments

comments