The last ice age led to the emergence of the woolly mammoth and a huge increase in glaciers. But he was only one of many that have cooled the Earth throughout its 4.5 billion years of history. So how often does the planet get swept up by ice ages, and when can we expect the next?
The main periods of glaciation in the history of the planet
The answer to the first question depends on whether you mean the large glaciations or the small ones that occur during these extended periods. Throughout history, the Earth has experienced five great periods of glaciation, some of which lasted for hundreds of millions of years. In fact, even now the Earth is experiencing a large period of glaciation, and this explains why it has polar ice. The five main ice ages are the Huronian (2.4-2.1 billion years ago), the Cryogeny glaciation (720-635 million years ago)), Andean-Sahara (450-420 million years ago), glaciation of the Late Paleozoic (335-260 million years ago) and Quaternary (2.7 million years ago to the present).
These large periods of glaciation can alternate between smaller ice ages and warm periods (interglacial). At the beginning of the Quaternary glaciation (2.7-1 million years ago), these cold ice ages occurred every 41 thousand years. Nevertheless, in the last 800 thousand years, significant ice ages have appeared less often - approximately every 100 thousand years.
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How does the 100,000 year cycle work?
Ice sheets grow for approximately 90,000 years and then begin to melt during a 10,000-year warm period. Then the process is repeated.
Given that the last ice age ended about 11,700 years ago, perhaps it's time to start another one? Scientists believe that we should be experiencing another ice age right now. However, there are two factors related to the Earth's orbit that influence the formation of warm and cold periods. Considering also how much carbon dioxide we emit into the atmosphere, the next ice age will not begin for at least 100 thousand years.
What Causes the Ice Age?
A hypothesis put forward by the Serbian astronomer Milutin Milankovic explains why there are ice and interglacial cycles on Earth. Since the planet revolves around the Sun, the amount of light it receives from it is influenced by three factors: its tilt (which ranges from 24, 5 to 22.1 degrees for a cycle of 41,000 years), its eccentricity (a change in the shape of the orbit around the Sun, which fluctuates from the near circle to an oval shape) and its wobble (one complete wobble occurs every 19-23 thousand years).
In 1976, a landmark paper in the journal Science presented evidence that these three orbital parameters explain the planet's glacial cycles. Milankovitch's theory is that orbital cycles are predictable and highly consistent throughout the planet's history. If the Earth is going through an ice age, then it will be covered with more or less ice, depending on these orbital cycles. But if the Earth is too warm, no change will occur, at least with regard to the growing amount of ice.
What can affect the heating of the planet?
The first gas that comes to mind is carbon dioxide. Over the past 800,000 years, carbon dioxide levels have ranged from 170 to 280 ppm (meaning that out of 1 million air molecules, 280 are carbon dioxide molecules). A seemingly insignificant difference of 100 parts per million leads to the appearance of ice ages and interglacial periods. But carbon dioxide levels are much higher today than in past periods of fluctuations. In May 2016, the level of carbon dioxide over Antarctica reached 400 ppm.
The earth has gotten so hot before. For example, in the days of the dinosaurs, the air temperature was even higher than it is now. But the problem is that in the modern world it is growing at a record pace, since we have emitted too much carbon dioxide into the atmosphere in a short time. In addition, given that the rate of emissions is currently not decreasing, it can be concluded that the situation is unlikely to change in the near future.
Warming effects
The warming caused by the presence of this carbon dioxide will have big consequences, because even a small increase in the Earth's average temperature can lead to drastic changes. For example, the Earth was, on average, only 5 degrees Celsius colder during the last ice age than it is today, but this has led to significant changes in regional temperatures, the disappearance of a huge part of flora and fauna, and the emergence of new species.
If global warming leads to the melting of all the ice sheets in Greenland and Antarctica, the level of the oceans will rise by 60 meters, compared with today's levels.
What Causes Great Ice Ages?
The factors that caused long periods of glaciation, such as the Quaternary, are not well understood by scientists. But one idea is that a massive drop in carbon dioxide levels could lead to lower temperatures.
So, for example, in accordance with the hypothesis of uplift and weathering, when plate tectonics leads to the growth of mountain ranges, new unprotected rock appears on the surface. It is easily weathered and disintegrates into the oceans. Marine organisms use these rocks to create their shells. Over time, rocks and shells take carbon dioxide from the atmosphere and its level drops significantly, which leads to a period of glaciation.
