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Ice ages: Why North America is key to their coming and going

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In a tiny fraction of the time it takes to build continental-scale ice sheets, the sheets retreat to high-latitude havens atop Greenland and the northern reaches of the Canadian archipelago.

The study, led by Ayako Abe-Ouchi, a climate scientist at the University of Tokyo and the National Institute of Polar Research, resulted from a unique approach to modeling ice ages.

The study provides "good insights that clearly advance our understanding" of ice ages, notes Penn State University glaciologist Richard Alley, who was not involved in the study, in an e-mail. It also confirms aspects of ice ages that researchers have well in hand, he says.

The approach linked individual atmosphere, crust, and ice models in a way that needed only information on the amount of sunlight reaching Earth to generate ice-sheet behavior over the past 400,000 years that geologists have gleaned from more than a century of field studies.

Changes in the amount of solar radiation striking Earth come with changes in Earth's orbit occurring at intervals of 41,000, 23,000, and 19,000 years.

The study reaffirms that changes in the amount of summer sunlight striking northern high latitudes sets the process in motion. Indeed, changes to the shape of Earth's orbit over time, as well as long-term changes in the orientation of its axis, and their impact on solar radiation at high northern latitudes were the most significant astronomical influences in the team's simulations.

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