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“Snowballs” could be triggered by the incoming sunlight – “Be careful at speed”



Snow globe Earth

The findings also suggest that exoplanets found in habitable zones may be sensitive to ice age.

At least twice in Earth’s history, almost the entire planet has been covered with a layer of snow and ice. These dramatic “Snowball on Earth” events occurred in rapid succession, somewhere around 700 million years ago, and evidence suggests that successive global ice ages paved the way for a subsequent explosion of complex multicellular life on Earth.

Scientists have considered several scenarios of what could have changed the planet into each ice age. Although no driving process has been identified, it is assumed that anything that caused a temporary stop must do so in a way that has moved the planet around a critical threshold, such as reducing incoming sunlight or atmospheric carbon dioxide to a level low enough to adjust. from the global expansion of ice.

but WITH Scientists now claim that the snowball was probably the product of “speed-induced icing.” This means that they have found that the Earth can be tilted into the global ice age, when the level of solar radiation it receives changes rapidly over a geologically short period of time. The amount of sunlight does not have to drop to a specific threshold; if the drop in incoming sunlight occurs faster than the critical speed, a temporary icing or snowball will follow.

These findings are published in Proceedings of the Royal Society, suggest that everything that triggered the Earth ‘s ice age most likely involved processes that rapidly reduced the amount of sunlight coming to the surface, such as large volcanic eruptions or biologically induced cloud formation that could significantly block the sun’ s rays.

Snow globe Earth

According to an MIT study, the trigger of the global ice age “Snowball Earth” may be drops in incident sunlight, which occurred geologically quickly. Credit: NASA, Christine Daniloff, MIT

The findings may also apply to the search for life on other planets. Scientists have been trying to find exoplanets in a residential area – a distance from their star that would be in a temperature range that could support life. A new study suggests that if there are sudden climate changes, these planets, like Earth, could temporarily freeze. Although located in a habitable zone, Earth-like planets may be more susceptible to the global ice age than originally thought.

“You could have a planet that stays well in the classic habitat, but if the incoming sunlight changes too quickly, you can get the Earth’s snowball,” said lead author Constantin Arnscheidt, a graduate student at MIT’s Department of Earth, Atmosphere and Planetary Sciences. (EAPS). “This is underlined by the fact that there is much more nuance in the concept of habitability.”

Arnscheidt was co-authored by Daniel Rothman, Professor of Geophysics at EAPS and co-founder and co-founder of the Lorenz Center.

Escape a snowball

Regardless of the specific processes that triggered the previous glaciation, scientists generally agree that the snowballs were created as a result of a “runaway” effect of feedback from the ice album: When the incoming sunlight decreases, the ice expands from the poles. at the equator. The more ice covers the globe, the more reflective or higher the planet in the albedo, which further cools the surface to spread more ice. Eventually, if the ice reaches a certain level, it becomes an escape, leading to global icing.

The global age of ice on Earth is temporary due to the planet’s carbon cycle. If the planet is not covered with ice, the levels of carbon dioxide in the atmosphere are to some extent regulated by the weathering of rocks and minerals. When the planet is covered with ice, the weather is greatly reduced, so that carbon dioxide accumulates in the atmosphere, creating a greenhouse effect that will eventually melt the ice age planet.

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

“There are a lot of ideas that caused these global icing, but they’re all really shrinking to an implicit change in incoming sunlight,” says Arnscheidt. “But in general, it was examined in the context of exceeding the threshold.”

He and Rothman had previously studied other periods in Earth’s history in which the rate or speed at which certain climate changes occurred played a role in triggering events such as mass extinctions in the past.

“During this exercise, we realized that there was an immediate way to do it in a serious way when such speed-guessing ideas were applied to the Earth’s snowball and its habitability,” says Rothman.

“Watch your speed”

Scientists have developed a simple mathematical model of the Earth’s climate system that includes equations representing the relationships between incoming and outgoing sunlight, the Earth’s surface temperature, the concentration of carbon dioxide in the atmosphere, and the effects of weathering in introducing and storing atmospheric carbon dioxide. The scientists were able to fine-tune each of these parameters and observed what conditions created a snowball.

Eventually, they found that the planet was more likely to freeze if the incoming sunlight was declining rapidly, at a speed that was faster than the critical speed, and not to a critical limit or a specific level of solar radiation. Exactly such a critical measure would be uncertain, as this model is a simplified representation of the Earth’s climate. Nevertheless, Arnscheidt estimates that the Earth would have to experience about a 2 percent drop in incoming sunlight over about 10,000 years to enter the global ice age.

“It is reasonable to assume that previous glaciations were caused by geologically rapid changes in solar radiation,” says Arnscheidt.

Specific mechanisms that may have darkened rapidly or over tens of thousands of years still need to be discussed. One possibility is that extended volcanoes could disperse the aerosol into the atmosphere and block incoming sunlight around the world. Another possibility is that primitive algae may have developed mechanisms that facilitated the formation of light-reflecting clouds. The results of this new study suggest that scientists may see processes such as these, which rapidly reduce incoming sunlight, as more likely triggers for the Earth’s ice ages.

“Even if humanity does not cause the snowball to ice on our current climate trajectory, the existence of such a ‘perversion point caused by peace’ on a global scale may still be a cause for concern,” Arnscheidt said. “For example, it teaches us that we should be careful about the speed at which we modify the Earth’s climate, not just the magnitude of change. There could be other such points that could be caused by anthropogenic warming. Identifying them and limiting their critical measures is a useful goal for further research. “

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

This research was partly funded by the MIT Lorenz Center.




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