If we could see the planet’s last 2.6 million years at super-fast film speed, we’d see polar ice sheets expanding over North America and northern Europe and retreating, expanding and retreating. Without benefit of satellite video from the last couple million years, researchers at three universities worked on the challenge of predicting when an ice age ends and when interglacial, or warming, periods begin.
According to a new study published today in Nature, climate scientists from University College London, University of Cambridge and University of Louvain (France) found answers based on solar energy peaks.
These occur when Earth’s orbit and the tilt of its axis result in ice-melting solar energy over our high northern latitudes. We’ve had 110 of these solar energy peaks in the last 2.6 million years, but only 50 of them triggered complete meltdown of the expanding ice sheets.
“The basic idea is that there is a threshold for the amount of energy reaching high northern latitudes in summer,” said Professor of Geography Chronis Tzedakis at UCL. “Above that threshold, the ice retreats completely and we enter an interglacial.”
This ice-melt threshold tended to occur in our planet’s earlier days about every 41,000 years. But things changed around a million years ago. From then up to now, the ice ages have expanded.
The university researchers were able to formulate a predictive model based on solar energy and the ice cycles to predict the end of an ice age and onset of interglacial periods over the last million years, finding that they occurred roughly every 100,000 years.
The scientists also found that some of these solar energy peaks almost triggered interglacial periods, but didn’t quite hit the threshold. This is where things get a little dicey.
“The threshold was only just missed 50,000 years ago,” said researcher Professor Michel Crucifix of the University of Louvain. “If it hadn’t been missed, then we wouldn’t have had an interglacial in the last 11,000 years.”
And you thought your winters were cold now.
By David Searls, Earth.com Staff Writer