Evrim Yazgin
Cosmos science journalist
Climatologists have matched small changes in the Earth’s orbit around the Sun over millions of years with ice age cycles. They have used this to predict when the next ice age is meant to take hold but say that anthropogenic climate change might have disrupted the cycle.
Earth has followed a pattern of alternating ice ages (glacial period) and interglacial periods for the last 2.5 million years.
The last glaciation ended about 11,700 years ago.
Serbian astronomer and geophysicist Milutin Milanković was the first to suggest that changes in Earth’s orbit and rotation affecting the amount of solar radiation reaching the planet could be behind ice ages in prehistory.
He published his ideas in a series of papers and a 1941 book called Canon of Insolation and the Ice-Age Problem. It was not until the 1970s that Milanković cycles – as they came to be known – were experimentally proven.
But which of Earth’s orbital and rotational parameters plays the most important role in these cycles? The new research published in the journal Science seeks to answer this question.
There are 3 main geometric factors – each with distinct cycle lengths.
The tilt of Earth’s rotational axis with respect to the plane of the planet’s rotation is called “obliquity”. Changes in obliquity have an observed period of roughly 41,000 years.
The direction of Earth’s rotational axis also wobbles, causing another cycle which lasts about 21,000 years. This wobble is called “precession”.
Finally, “eccentricity” is the shape of Earth’s orbit which goes from being more or less circular every 100,000 years.
The authors of the new paper found a predictable pattern for glaciation periods in the last 900,000 years. They found that an interplay of the phases of precession, obliquity and eccentricity all contribute to a 100,000-year-ice age cycle.
Precession is the primary driver of the end of ice ages, while obliquity plays the dominant role for the beginning of ice ages.
The result is that ice ages have a roughly 21,000-year cycle with their relative intensity determined by whether the lining up of each cycle.
“The pattern we found is so reproducible that we were able to make an accurate prediction of when each interglacial period of the past million years or so would occur and how long each would last,” says lead author Stephen Barker from Cardiff University in the UK.
“This is important because it confirms the natural climate change cycles we observe on Earth over tens of thousands of years are largely predictable and not random or chaotic.”
We are now living in an interglacial period. According to the new research, we would ordinarily be expecting the next ice age to be in about 10,000 years.
The researchers say, however, that current warming trends would prevent a normal shift into a glacial period.
“But such a transition to a glacial state in 10,000 years’ time is very unlikely to happen because human emissions of carbon dioxide into the atmosphere have already diverted the climate from its natural course, with longer-term impacts into the future,” says co-author Gregor Knorr from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research in Germany.
