“Snowball Earth” may have been triggered by a dip in the incoming sun – “beware of speed”


The finding also suggests that exoplanets lying within habitable areas may be susceptible to ice ages.

At least twice in the history of Earth, almost the entire planet was covered in a sheet of ice and snow. These dramatic “snowball earth” events occurred in quick succession, some 700 million years ago, and evidence suggests that the persistent global ice age set the stage for the subsequent eruption of complex, multicellular life on Earth.

Scientists have considered several scenarios for what might happen to the planet in each ice age. While not a single driving process has been identified, it is believed that whatever has been done to trigger temporary freeze-overs must occur in a way that moves the planet beyond a critical threshold, Such as setting sufficient levels to reduce incoming sunlight or atmospheric carbon dioxide. Global Expansion of Ice.

but MIT Scientists now say that snowball Earth was the product of “rate-induced glaciers”. That is, they found that the Earth could be transported to a global ice age when solar radiation levels quickly attained changes in a geologically short period of time. The amount of solar radiation does not have to go up to a particular boundary point; A temporary glacier, or snowball Earth, will follow as long as the decrease in incoming sunlight intensifies at a significant rate.

These findings, published in Proceedings of the Royal Society A., Suggest that whatever triggers Earth’s ice ages, they most likely involve processes that reduce the amount of solar radiation coming to the surface, such as widespread volcanic eruptions or biologically induced Cloud formation that could have blocked the sun’s rays to a great extent.

Snowball earth

“Snowball Earth” could be the trigger for the global ice age to be drops in the incoming sun that according to an MIT study, was geologically early. Credit: NASA, Christine Daniloff, MIT

The findings may also apply to the discovery of life on other planets. Researchers are keen to find exoplanets within the habitable zone – a distance from their star that will be within a temperature range that can support life. New studies suggest that these planets, like Earth, may temporarily snow if their climate suddenly changes. Even if they lie within a habitable zone, Earth-like planets may be susceptible to previously thought global ice ages.

“You can be a planet that lives well within the classical habitable zone, but if the incoming sun changes very fast, you can get a snowball Earth,” says lead author Constantin Arnscheid, who MIT has undergraduate students in the Department of Earth, Atmospheric and Planetary Sciences. (EAPs). “Does it highlight that there is a very subtle difference in the concept of residence?”

Arnscheidt co-authored with Daniel Rothman, EAPS Professor of Geophysics, and is co-founder and co-director of the Laurence Center.

A running snowball

Despite particular processes arising from previous glaciers, scientists generally agree that snowball Earth originated from a “runoff” effect, including an ice-albedo feedback: as the incoming sun subsides, from the poles. Snow spreads to the equator. As more snow covers the globe, the planet becomes more reflective, or higher in the albedo, which further cools the surface for more ice to expand. Eventually, if the ice reaches a certain threshold, it becomes a fugitive process, resulting in a global glacier.

The global ice ages on Earth are temporary in nature, due to the planet’s carbon cycle. When the planet is not covered in ice, the level of carbon dioxide in the atmosphere is controlled to some extent by weathering of rocks and minerals. When the planet is covered in ice, the weathering reduces to a great extent, causing carbon dioxide to form in the atmosphere, creating a greenhouse effect that eventually ejects the planet from its ice age.

Scientists generally agree that the formation of snowball Earth has something to do with the balance between incoming sunlight, the ice-albedo reaction and the global carbon cycle.

“There are a lot of considerations due to these global glaciers, but they all really boil down to some inherent modification of solar radiation,” says Arnschet. “But generally it has been studied in the context of crossing a border.”

He and Rothman had previously studied other periods in Earth’s history where the speed, or rate at which certain changes in climate occurred, had a role in triggering events such as the extinction of previous events.

“During this exercise, we felt that snowball was an immediate way to make a serious point by applying such ideas of rate-induced tipping to meaning and habitat,” Rothman says.

“Beware of speed”

Researchers developed a simple mathematical model of the Earth’s climate system to represent the relationship between incoming and outgoing solar radiation, the Earth’s surface temperature, the concentrations of carbon dioxide in the atmosphere, and weathering’s effects in weathering. Contains equations for. Storage of atmospheric carbon dioxide. Researchers were able to consider each of these parameters under which conditions they could generate snowball meanings.

Finally, they found that a planet was likely to freeze if incoming solar radiation quickly subsided, at a faster rate than a critical rate, but rather from a significant range or particular level of sunlight. There is some uncertainty in the fact what the critical rate will be, as the model is a simplified representation of the Earth’s climate. Nevertheless, Arnschet estimates that the Earth would have to experience a 2 percent drop in incoming sunlight over a period of about 10,000 years in order to tip in the global ice age.

“It is fitting that the previous glaciers were driven by geologically accelerated changes in solar radiation,” says Arnshechid.

The special mechanism that can quickly blacken the sky in tens of thousands of years is still up for debate. One possibility is that widespread volcanoes can spew atmospheres into the atmosphere, preventing worldwide sunlight. Another is that primitive algae may have evolved mechanisms that facilitate the creation of clouds that reflect light. The results of this new study suggest that scientists may consider these processes, which may reduce incoming solar radiation, as the Earth is more likely to have ice ages.

“Even though humanity will not trigger a snowball glacier on our current climate trajectory, the existence of such a ‘rate-induced tipping point’ on a global scale can still be a concern,” explains Arnschet. For example, it teaches us that we must be mindful of the speed at which we are modifying the Earth’s climate, not just the magnitude of change. There may be other rate-induced tipping points that may be triggered by anthropogenic warming. Identifying these and reducing their critical rates is a meaningful goal for further research. “

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Reference: “Pathways to Global Glaciation”, 29 December 2020, by Constantin W. Arnscheid and Daniel H. Rothman Proceedings of the Royal Society A..
DOI: 10.1098 / rspa.2020.0303

The research was funded, in part, by the MIT Lorenz Center.

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