A plunge in incoming sunlight may have triggered 'Snowball Earths' | Hacker News Reader

A plunge in incoming sunlight may have triggered 'Snowball Earths'

phys.org

44 pointspseudolus22 comments

There are many really interesting episodes in Earth's history. The one that I'm really fascinated by lately is the so called Azolla Event, in which it is hypothesized that Azolla aquatic ferns at the North Pole at the beginning of the Eocene soaked up carbon from the atmosphere, to be deposited on the sea floor, taking the earth from a hothouse (where the poles were above freezing) to an icehouse.

https://en.wikipedia.org/wiki/Azolla_event

It begins to look like every large drop in atmospheric carbon is linked to photosynthesis, in one way or another.

You may find the Great Oxygenation Event from my book to be of relevance (it supports what you're saying):

https://impacts.to/preview.html

If you'd rather read it as a PDF instead of images:

https://impacts.to/downloads/lowres/impacts.pdf

Volcanoes seem like most likely culprit. Although, I wonder if there was evidence of reduced geomagnetism which increased cosmic ray cloud nucleation via the Svensmark Effect. See:

Winter monsoons became stronger during geomagnetic reversal https://www.sciencedaily.com/releases/2019/07/190703121407.h...

The Milankovitch cycles[1] almost certainly play a significant role. The arrangement of the continents also has a huge effect on climate, because an Earth with only one large ocean transfers heat much differently than one with two major oceans. It's largely because of the positions of the continents, including a large polar continent, that we are still in an ice age[2]. However an event like a massive volcanic discharge could conceivably start a positive feedback loop of cooling. Since ice has a high albedo, we could get a runaway, well, snowball effect.

[1] https://en.wikipedia.org/wiki/Milankovitch_cycles [2] https://en.wikipedia.org/wiki/Quaternary

This is a strange result -- it's saying that an ice age could be caused by a change in sunlight. With made up numbers, it's saying that a change from 100W/m2 to 60W/m2 could cause an ice age, even though a stable regime at 60W/m2 would not create an ice age. Even if it just claims that a change in temp speeds the onset of an ice age that's surprising to me.

The positive gain from albedo feedback has been well-known for quite some time. Its part of why the Arctic is heating up so much faster than the rest of the world right now.

The negative gain from weathering and volcanism is also quite well-known.

The authors of this paper put 2 and 2 together and showed that you only need a brief period of reduced insolation to trigger a snowball earth, and that once insolation returns to normal it can stay in the snowball state for much longer.

Hysteresis[1].

[1] https://en.wikipedia.org/wiki/Hysteresis

Weird question, how large would an alien spaceship have to be to position itself between the sun and the earth and cause us major problems? Distance would also play a factor as would the degree of “major problem” (varying effects on plant life/temperature). The equivalent of finding a parked car in front of your driveway, on a cosmic scale.

Would be fun to learn the mathematics, physics, and macrobiology to solve this!

An object capable to completely shade Earth must be larger than Earth itself. The Moon can only shade a small fraction of Earth at a time, see eclipse path maps, for example https://www.timeanddate.com/eclipse/map/2024-april-8.

This is plainly untrue.

Hold a finger up in front of a torch, and look at the size of the shadow cast. Move the finger closer to the torch, and watch the shadow area increase.

A shadow is always larger than the light-facing area of the object blocking the light. This is true even of your own shadow in sunlight, even though your distance from the light source means the change is so tiny you don't even notice it.

                      ------
                ------     S
          ------           S
    ------     A           S
    E          A           S
    ------     A           S
          ------           S
                ------     S
                      ------

    *drawing not to scale

For the shadow to be significantly larger than the shading object, the object must be significantly closer to the light source.

For Earth, in solar orbit, that means you'd have to get inside the orbit of Venus.

Then you have a huge energy cost in keeping your shading object in the correct position relative to Earth. Its natural orbit is not going to work at all.

A finger is comparable size to a torch. Not much light goes around a finger despite the non-zero size of the light source making the rays both non-parallel and originating from different places.

Sol has a diameter of ~100 times the Earth. A shade near Earth would have to be similar size to Earth to block most of the light, and likewise similar size to Sol if it was near Sol.

That's a good point. I made the mistake of treating the sun as a point light source, which of course it is not! https://www.timeanddate.com/eclipse/shadows.html explains the difference clearly.

My guess is the actual sun has periods of less activity / heat.

How would that even be possible on these scales?

The article mentions in the end that the opposite effect of rapid warming-up might be possible, tripped by a similar rapid spike in one of the global climate variables.

A large asteroid is the obvious possibility to create such an event

I doubt the dust from a large impact would stay in the atmosphere long enough to trigger a snowball earth. It didn't happen with the Chicxulub impact/non-avian dinosaur extinction.

All life that survived snowball Earth has genes that improves health in cold temperatures, and this has been documented in humans as well.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4486781/

The article you cited makes no claims about 'all life having genes that improve its health in cold temperatures'.

The leap between its claim, and yours, is massive, and would require incredibly extraordinary evidence.

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