Research Article: Are Ice Age Cycles of the Northern Hemisphere Driven by Processes in the Southern Hemisphere

Viewpoint: Yes, ice age cycles of the Northern Hemisphere are driven by complex forces in the Southern Hemisphere, and possibly even the tropics.

Viewpoint: No, the ice age cycles of the Northern Hemisphere are not driven by processes in the Southern Hemisphere; the Milankovitch cycle and disruption of the ocean's thermohaline circulation are the primary initiators.

Ice-age conditions—with a global temperature 9°F (5°C) lower than today's climate and glaciers that cover most of Europe, Asia, and North and South America in a deep blanket of ice—have predominated for 80% of the past 2.5 million years.

Ice ages come in 100,000-year cycles controlled by the shape of Earth's orbit around the Sun. The shape varies, becoming more circular or elliptical every 100,000 years. In the 1870s, the Scottish physicist James Croll suggested that ice ages were caused by insolation, or changes in the amount of solar radiation at the poles as...
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