The primary trigger for the end of the last Ice Age was a shift in Earth's orientation toward the sun, which occurred approximately 20,000 years ago, leading to the melting of large ice sheets in the Northern Hemisphere.
While the shift in Earth's orbit was the initial trigger, the melting process was a complex interaction of several factors:
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Milankovitch Cycles: These are cyclical changes in Earth's orbit and axial tilt that affect the amount and distribution of solar radiation received. Changes in these cycles gradually increased the amount of sunlight reaching the Northern Hemisphere during the summer months.
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Increased Solar Radiation: This increased solar radiation directly warmed the ice sheets, initiating melting.
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Positive Feedback Loops: As the ice sheets began to melt, several positive feedback loops amplified the warming:
- Albedo Effect: Ice reflects a large portion of incoming sunlight (high albedo). As ice melts, it exposes darker surfaces (land or water) that absorb more sunlight, further increasing warming.
- Greenhouse Gas Release: Melting permafrost released trapped greenhouse gases like carbon dioxide and methane, contributing to further warming.
- Ocean Currents: The influx of fresh meltwater into the North Atlantic disrupted ocean currents like the Gulf Stream. The reference suggests this weakened the Gulf Stream and drove the north back into the ice age, but this is a localized and temporary effect. The overall global trend was towards warming.
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Changes in Ocean Circulation: Meltwater runoff altered ocean salinity and density, affecting ocean currents and heat distribution around the globe.
In summary, the melting of the Ice Age ice was initiated by changes in Earth's orbit that increased solar radiation, and then accelerated by various feedback mechanisms that amplified the warming effect.
