Carbon Dioxide Ended Last Ice Age
from the National Center for Policy Analysis:
About 10,000-20,000 years ago, Earth started to emerge from a quarter million years of deep freeze as the terrestrial ice sheet rolled back and warmer temperatures prevailed. A fundamental question in this event is what was the primary trigger that caused the world to gradually warm to its contemporary state, says ABC Science.
There have traditionally been two parties to this discussion that rely on similar external occurrences but different subsequent mechanisms to explain the earth’s warming.
- The first group believes that the earth underwent a gradual orbital change, bringing it closer to the sun, which subsequently warmed the planet and caused slow deglaciation.
- The second group acknowledges that the world likely did undergo some sort of orbital shift, but that this was not sufficient to begin a warming cycle — they argue instead that this triggered a series of events that caused the release of carbon dioxide (CO2), and that this gas was the primary driver.
It can seem difficult to parse the two theories given that they agree upon many of the same events in explaining their respective theories. However, new data collected from 80 ice cores around the world, which show that CO2 increased suddenly during the deglaciation process, suggest that the second group may be correct. Dr. Jeremy Shakun of Harvard University explains the precepts of the theory:
- Shakun and colleagues theorize that orbital shift boosted sunlight that warmed the northern hemisphere between 21,500 and 19,000 years ago.
- This caused some of its ice sheet to melt and spill gigatons of chilly freshwater into the North Atlantic.
- The big gush had a dampening effect on the Atlantic meridional overturning circulation, a well-known “conveyor belt” by which warm water travels northwards on the Atlantic’s surface.
- When the current braked, warm water began to build up in the southern Atlantic, where it swiftly started to warm up Antarctica and the Antarctic Ocean.
- Warming the south in turn shifted the wind and melted sea ice, releasing some of the vast amounts of CO2 that had been absorbed by the ocean and stored in its depths.
This CO2 release, they theorize, was the crucial trigger that turned this relatively insignificant orbital shift into a gradual global warmer that made the planet more hospitable.
Source: “Carbon Dioxide Ended Last Ice Age: Study,” ABC Science, April 5, 2012.
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