Imagine the Chicago Skyline building. Now imagine it’s almost 2 miles (3km) under the ice. That is the view of Earth at the coldest point of the last Ice Age.
Given the recent geological history of the Earth, this would not be an unusual sight. Over the past 2.6 million years (aka the Quaternary Period ), the planet has experienced more than 50 ice ages, with interspersed periods of interwar warming.
But what causes ice sheets and glaciers to periodically grow? Ice ages were driven by a complex, interconnected set of factors related to Earth’s position in the solar system and more local influences, like CO2 levels in the atmosphere. Scientists are still trying to understand how this system works, especially as human-caused climate change may have broken this cycle forever.
Ice ages are driven by a complex set of factors.
It wasn’t until a few centuries ago that scientists began to recognize evidence of a frozen past . In the mid-19th century, Swiss-American naturalist Louis Agassiz documented the marks that glaciers left on Earth, such as out-of-place rocks and broken plates. giants, called morass , which he suspected were ancient glaciers that swept them away and pushed them away.
In the late 19th century, scientists named four ice ages that occurred during the Pleistocene Epoch, which lasted from about 2.6 million years ago until 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 cycle came in the 1940s, when Serbian astrophysicist Milutin Milankovitch proposed the so-called Milankovitch cycle , a study of the Earth’s motion are still used to explain climate change today.
Mark Maslin, professor of paleontology at University College London, says Milankovitch has outlined three main pathways through which the Earth’s orbit changes relative to the sun. These factors determine the amount of solar radiation (in other words, heat) reaching the planet.
Milankovitch determined that the orbital conditions that produce cool summers are particularly important precursors to ice ages. “There will always be ice in winter,” Maslin said. “To build an ice age, some of the ice has to last through the summer.”
But, to transition to the ice age, orbital phenomena alone are not enough. The real cause of an ice age is the underlying 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 levels of greenhouse gases in the atmosphere play a role. important.
For example, scientists at the Potsdam Institute for Climate Impact Research (PIK) in Germany have shown that the triggers of previous ice ages were triggered mainly by a dramatic reduction in CO2 in the atmosphere. It is the rapid increase in atmospheric CO2 caused by emissions from human activities that will likely prevent the onset of the next ice age within the next 100,000 years.
“Unlike any other force on the planet, the ice age has shaped the global environment and has since determined the development of human civilization,” said Hans Joachim Schellnhuber, then director of PIK. and co-author of one of the studies, said in a statement in 2016. “For example, we get the fertile soils and landscapes we are today because of the last ice age, The ice age left us rivers, glaciers, bays and lakes, but today it is humanity with fossil fuel emissions that will determine future development. future of the planet”.