Why did the Ice Age occur?

Imagine the Chicago Skyline building. Now imagine it's under the ice almost 2 miles (3 km) away. That is the view of the Earth at the most icy moment of the last Ice Age.

Imagine the Chicago Skyline building. Now imagine it's under the ice almost 2 miles (3km) away. That is the view of the Earth at the most icy moment of the last Ice Age.

Considering the recent geological history of the Earth, this would not be an unusual sight. Over the past 2.6 million years (also known as the Fourth Period ), the planet has experienced more than 50 ice ages, with intercontinental warming periods intermingled.

But what makes the glaciers and glaciers grow periodically?The ice age is driven by a complex , interconnected set of factors , related to the Earth's position in the solar system and more local influences, such as the level of CO 2 in the air. Scientists are still trying to figure out how this system works, especially when anthropogenic climate change may have disrupted this cycle permanently.

Picture 1 of Why did the Ice Age occur? Photo 1 of Why did the Ice Age occur?
Ice ages are driven by a complex set of elements.

It was not until several centuries ago that scientists began to recognize evidence of a frozen past . In the mid-19th century, Swiss-American naturalist Louis Agassiz recorded the marks that glaciers have left on Earth, like boulders that have been out of position and cracked pieces. giant, called moraine , which he suspected was ancient glaciers that swept away and pushed them away.

In the late 19th century, scientists named the four ice ages that occurred during the Pleistocene Era, which existed from about 2.6 million years ago to about 11,700 years ago. However, it was not until decades later that researchers realized that these cold periods were much more regular.

A major breakthrough in understanding the ice age occurred in the 1940s, when Serbian astrophysicist Milutin Milankovitch proposed the so-called Milankovitch cycle , a study of Earth's motion. Still used to explain climate change today.

Mark Maslin, a professor of paleontology at University College London, said Milankovitch outlined three main paths through which the Earth's orbit changes from the sun. These factors determine the amount of solar radiation (in other words, heat) to the planet.

  • First , the eccentricity of the Earth's orbit around the sun , changing from nearly circular to elliptical over a period of 96,000 years. Maslin explained: "The reason for the deformed orbit is because Jupiter, which accounts for 4% of the mass of the solar system, has strong gravitational force, moves the Earth's orbit out and then returns. ".
  • The second is the tilt of the Earth, which is why we have seasons . The Earth's axis of rotation allows one hemisphere to always tilt away from the sun (causing winter) while the other side is tilted toward it (causing summer). Maslin also said that this tilt angle changes over a period of about 41,000 years, changing the severity of the seasons. "If [the axis] is more upright, of course summer will be less hot and winter will be a bit colder."
  • Third, the wobble of the Earth's tilt axis , moving like a mahogany. Maslin said, "What happened is, the angular momentum of the Earth rotates so fast once a day that the axis also wobbles." The wobble happens every 20,000 years.

Milankovitch determined that the trajectory condition that creates cool summers is a particularly important precursor to the ice age. Maslin said: "There will always be ice in the winter. To build an ice age, part of the ice must exist throughout the summer."

But, to move on to an ice age, orbit alone is not enough.The real cause of an ice age is the fundamental response of the climate system . Scientists are still debating how different environmental factors affect the freezing and melting of ice, but recent research suggests that the level of greenhouse gases in the atmosphere plays a role. important.

For example, scientists at the Potsdam Institute for Climate Impact Research (PIK) in Germany have shown that glacial agents were previously triggered mainly by a significant reduction in CO 2 in The atmosphere and the rapid increase in CO 2 in the atmosphere due to emissions from human activities will likely prevent the start of the next ice age for the next 100,000 years.

"Unlike any other force on the planet, the ice age shaped the global environment and thus determined the development of human civilization," said Hans Joachim Schellnhuber, then PIK's director. and co-author of one of the studies, said in a statement in 2016. "For example, we have gained fertile land and landscapes today thanks to the last ice age, The ice age has left us with rivers, glaciers, bays and lakes, but today, humans with fossil-fuel emissions are the decisive factor in future development. hybrid of the planet ".

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