Regular changes in the Earth's orbit and the tilt of its axis may be responsible for the beginning and end of ice ages over the past 800,000 years. (Image credit: Gregory Adams/Getty Images)
New research confirms that changes in the Earth's tilt relative to the sun have driven the movement of vast ice sheets over the past 800,000 years, triggering the start and end of eight ice ages.
The new study found a “surprising correlation” between the Earth’s tilt and ice sheet formation, said lead author Stephen Barker. Based on this data, scientists estimate that the next ice age could begin in 11,000 years — if not for human-caused global warming.
“The prediction is that the next ice age could start within the next 10,000 years,” Barker, a professor of earth sciences at Cardiff University in the U.K., told Live Science. But that conclusion doesn’t take into account rising greenhouse gas emissions, which are heating the planet to the point where ice ages don’t happen, he added.
Ice ages, or glacials, are very cold periods of time that occur about every 100,000 years, covering much of the planet in huge ice sheets for thousands of years. These ice ages alternate with warmer interglacial periods, when the ice sheets retreat toward the poles. The Earth is currently in an interglacial period, with the last ice age reaching its maximum about 20,000 years ago.
Tilt and swing
Scientists used to think that the Earth's position and angle relative to the Sun influenced the formation of ice sheets. In the early 1920s, Serbian scientist Milutin Milankovic suggested that small changes in the tilt of the Earth's axis and the shape of its orbit could trigger large-scale glacial events.
Researchers have been testing Milankovitch's theory for the past century. Notably, a 1976 study found geological evidence that two Earth parameters—tilt and precession, or changes in the angle of the Earth's axis and how the axis wobbles, respectively—play a role in the expansion and contraction of ice sheets. However, the precise role of each parameter remained unclear.
Now Barker and his colleagues claim they have finally managed to understand the impact of these parameters.
Currently, the Earth's axis is tilted 23.5 degrees from vertical as it orbits the Sun, which affects the amount of solar energy reaching each pole. But the tilt of the Earth's axis naturally changes in a cycle that lasts about 41,000 years. The axis also wobbles like an off-center spinning top, which affects the amount of solar energy reaching equatorial regions in the summer over periods of about 21,000 years.
As part of the study, the scientists mapped known changes in tilt and precession over the past 800,000 years. They also tracked the expansion and retreat of ice sheets during that period using available data from microscopic shells known as foramines in ocean sediment cores. The relative abundance of certain types of oxygen in foramines indicates how far the ice sheets extended when these organisms were alive, Barker explained.
Sourse: www.livescience.com
