Scientists from UW-Madison have uncovered evidence in the high deserts of South America suggesting Earth's most recent ice age not only affected the Northern Hemisphere, but also influenced climates all over the world.
\The chronological data revealed a synchronous ice age worldwide, which is pretty surprising because we are now going into spring and summer while the Southern Hemisphere is going into the winter months,"" said Brad Singer, UW-Madison associate professor of geology and geophysics.
The findings are reported in the current issue of the Geological Society of America Bulletin, a leading Earth science journal.
""This finding is important to scientists because we are able to start addressing fundamental questions about past climates,"" assistant researcher Daniel Douglas said. ""These same questions also affect our ability to accurately predict future climate scenarios.""
The scientists used a procedure called cosmogenic surface exposure dating to determine the relative age of boulders dropped by glaciers as they advanced towards the equator more than 20,000 years ago. This new method uses high-energy cosmic rays to determine the amount of time glacial debris have been exposed at the surface. Douglas said this technique was the group's only option because it could not find any organic material that could be radiocarbon tested.
While the exact causes of ice ages are unknown, scientists believe they are related to fluctuations in the amount of solar radiation reaching the Earth from the sun.
""The ice ages coincide with periods of decreased solar radiation caused by slight variations in Earth's orbit around the sun like a top that has slowed and has started to wobble a bit,"" Douglas said.
A decrease in carbon dioxide could also have caused ice ages. However, in the past century, carbon dioxide emissions have skyrocketed, causing temperatures worldwide to rise.
""Without the natural records we have helped to establish here, we can't gauge the full consequences of non-natural effects [such as carbon dioxide] on the Earth,"" Singer said.
Some scientists speculate there is a chance global warming could be overcome by another ice age, but the odds are remote.
""Anthropogenic climate change happens on the time scales of decades to centuries, whereas ice ages take thousands to tens of thousands of years to develop,"" Douglas said. ""The estimated cooling at the last ice age maximum is about four degrees Celsius. Computer simulations predict a 2.5 degree increase in temperature during the next century. We appear to be in control of our own destiny.\
