The mysterious shift that locked Earth into a 100,000-year ice cycle
In short: For millions of years, Earth's climate has pulsed between ice ages and warm periods. But about one million years ago, the rhythm suddenly changed. Scientists are now uncovering how a collapse in ocean currents and the way glaciers grip the land may have rewritten our planet's climate destiny.
The primary driver of Earth's long-term climate cycles is the Milankovitch Cycles—periodic changes in our planet's orbit and orientation toward the Sun. These astronomical shifts dictate how much solar energy the Earth absorbs. However, these cycles alone do not explain the current pacing of our ice ages. For much of the last 2.6 million years, the planet fluctuated between glacial and interglacial periods every 41,000 years.
A pivotal turning point occurred roughly one million years ago, known as the Mid-Pleistocene Transition (MPT). During this period, the frequency of ice ages shifted to the 100,000-year cycle we see today. Because the Milankovitch Cycles did not change during this time, researchers believe a different mechanism was at work. Evidence suggests a major shift occurred in how the Earth's climate system responded to those orbital variations, leading to much more intense ice sheets in the Northern Hemisphere.
New geochemical data from deep-sea sediments in the Atlantic Ocean points toward a potential culprit: the Atlantic Meridional Overturning Circulation (AMOC). This massive system of ocean currents moves heat toward the North Atlantic. Around the time of the MPT, the AMOC experienced a severe weakening. This slowdown, combined with changes in ice sheet thickness and glacial erosion, may have caused ice sheets to stick to the bedrock more effectively, creating the feedback loops necessary to sustain massive, long-lasting glaciers.
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Sources
- Summary by Intellect · source: Earth's Greatest Climate Mystery: Why Ice Ages Return Every 100,000 Years | Full Documentary
- Also: Why did glacial cycles intensify a million years ago?
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