Rapid loss of sunlight could have triggered snowball events in the past

Not all glaciations are equally brutal. In the most extreme glaciation events known to science, ice spreads from Earth’s polar regions and spreads to lower latitudes, literally reshaping the face of the planet.

Evidence of such epic transitions can be found in the geological record, most recently in formidable glaciations during the cryogenic period. Scientists think that these extreme cooling events had potentially global reach and ramifications: a phenomenon called ‘Snowball Earth’.

But what the hell could unleash a cold so devastating and unforgiving that most, or all, of our planet would end up wrapped in a frozen sphere of ice and snow? While the exact triggers remain unknown, researchers have uncovered a new theoretical explanation for how such a thing could happen.

“There are many ideas about the cause of these global glaciations, but they all boil down to an implicit modification of the incoming solar radiation,” says planetary science researcher Constantin Arnscheidt at MIT.

“But it’s generally been studied in the context of crossing a threshold.”

In other words, the conventional explanation for how a Snowball Earth could transpire is that, in some kind of cataclysmic shadow cast, a reduced amount of sunlight would hit the planet’s surface, resulting in a colder Earth freezing .

Another hypothetical explanation, having to do with the carbon cycle, would be the opposite of the global warming crisis facing Earth now: what if our planet had so little carbon dioxide that it traps heat in the atmosphere that we lose completely the temperate climate of the Earth, with its heat? adrift in space?

“Although there is still debate about the specific triggers for low-latitude glaciations in Earth’s geological past, there is a general understanding that glaciation begins when changes in radiative fluxes or CO2 fluxes exceed a critical threshold. “Arnscheidt and his co-author, MIT Geophysicist Daniel Rothman, explains in a new article.

While the theory has focused on such critical thresholds previously, researchers have found a new avenue to think about Snowball Earth’s precursors: what would happen if a critical threshold was not met (in terms of solar radiation decay, by example), but was a critical rate of change reached?

In a new model, the researchers simulated Earth’s dynamic systems in glaciation scenarios, primarily the interaction of ice-albedo feedback and the carbonate-silicate cycle.

The first is an example of positive feedback. As Earth gets colder and closer to Snowball Earth, its icy ice and snow cap ends up reflecting more sunlight away from the planet, which in turn accelerates the cooling effects already underway.

However, as the Earth becomes colder, our usual carbonate-silicate cycle is disrupted. With Earth’s rocks sealed under ice, they are less able to absorb atmospheric carbon, so it stays in the air trapping heat. That is why, anyway, at a distance from Earth from the Sun, our planet in theory would not be trapped in a permanent Snowball state, despite the perpetuation of ice-albedo feedback.

With these types of factors incorporated into their models, the researchers examined whether the frequency-induced tip could induce a Snowball Earth event. Under the right circumstances, it did.

In the simulations, Arnscheidt and Rothman discovered that if solar radiation fell fast enough long enough, that in itself might be enough to unleash a Snowball Earth, and all it would take would be a 2 percent drop. percent of sunlight on the surface over 10,000 years, the researchers estimate.

In the grand scheme of things (read: approximately 4.5 trillion Earth years), that’s not very long. But what could Earth hide from the Sun like that, for 10,000 years in a row?

No one knows for sure, but it is plausible that something like a planetary-scale volcanic winter unleashed by volcanic eruptions could cloud our atmosphere enough. Alternatively, some sort of biological phenomenon in Earth’s ancient past, like a wave of moisture-producing algae, could generate condensation clouds that could eventually freeze them and everything else forgotten.

Of course, all of these ideas are quite pretty. But that doesn’t mean that we shouldn’t go looking for what might have caused Snowball Earth to unfold, or explore how quickly this ancient and icy story could have unfolded.

Especially since we are now running so fast in the opposite direction, the researchers say.

“It teaches us that we must be careful with the speed at which we are modifying Earth’s climate, not just with the magnitude of the change,” says Arnscheidt.

“There could be other velocity-induced tipping points that could be caused by anthropogenic warming.”

The findings are reported in Proceedings of the Royal Society A.