In the history of planet Earth the climate has swung between “warm and wet” and “ice age.” One of the great mysteries of paleoclimatology is “what triggers the transitions between warm and wet and ice age?” I’m sure there are others out there who have multiple publications on this point, but despite my training in biology and chemistry I’m not a true expert in the fields of cosmology, astrophysics, or some of the other disciplines that I’m writing about here. So if you are an expert in those fields, and I get something wrong, please feel free to leave a comment.
“What Causes Ice Ages?” https://www.pbs.org/wgbh/nova/article/cause-ice-age/ To sum up the pbs article, it could be a complex myriad of everything from plate tectonics to CO2, but in the end it’s a big shrug of “we don’t really now.”
I think that now I can offer some of the mechanisms that trigger these switches between warming and cooling. First up, lets talk about going from “warm and wet” to “ice age.”
Solar output is not a constant, CO2 content of the atmosphere is not a constant, and the albedo of the planet is not a constant. Of these three variables, CO2 is irrelevant to going from “warm and wet” to “ice age” when the following conditions occur.
1. Solar output minimizes and decreases energy output and decreases the intensity of the “solar wind” which helps lower the “flux” of cosmic radiation reaching earth. This directly causes a decrease in solar energy to reach the surface. https://aasnova.org/2017/12/01/a-shifting-shield-provides-protection-against-cosmic-rays/
2. More cosmic radiation reaches earth, and the increase in cloud seeds causes a statistically significant increase in cloud cover. This changes the albedo of the planet so that even less solar energy reaches the surface. https://physicsworld.com/a/physicists-claim-further-evidence-of-link-between-cosmic-rays-and-cloud-formation/
3. With less energy coming from the sun, and more energy reflecting off of clouds, the planet goes into a cooling cycle, increasing the snow pack and increasing the size of glaciation on the planet. Think of clouds as just “insulation” that slows energy in, and slows energy out. http://www-das.uwyo.edu/~geerts/cwx/notes/chap09/rossow.html
4. When solar output increases, if conditions 1-3 have gone on long enough, now there is enough highly reflective snow/ice on the surface of the planet to maintain the “ice age” even in with fewer clouds and higher solar output.
5. When the planet is in an “ice age” state, the oceans cool and cool liquid can hold more gas than hot liquid, so the atmospheric CO2 content shifts to the oceans, and decreases. If atmospheric CO2 decreases to the point where plant life starts to be impacted, we may be able to hit the transition point from “ice age” to “warm and wet.”
Everybody follow that logic?
The steps to get out of an ice age. I have less confidence in this because I hate to reference anyone whose published works include crap like “Thoth, Architect of the Universe” as the primary source of this explanation. But just because I don’t like the credentials of the source doesn’t mean that I can ignore the logic of the argument. However, this is the primary paper that makes a logical explanation of events: https://www.sciencedirect.com/science/article/pii/S1674987116300305
1. The sun has to be in a high output cycle to increase the solar winds to lower the cosmic ray “flux” reaching earth, which lowers overall cloud cover. This allows more energy to reach the surface.
2. The ice age had to have gone on long enough to deplete atmospheric CO2 to the point where plant life begins to die off, desertification begins, and large amounts of dust can become airborne and fall onto the ice and snow, changing the albedo of the planet (the exact same mechanism as “black carbon/soot” changes the albedo of the poles from commercial shipping exhaust, https://e360.yale.edu/features/carl_zimmer_black_carbon_and_global_warming_worse_than_thought ).
3. The solar output remains high enough to warm the surface of the planet to the point where glaciers and snow fields recede, and oceans begin to warm.
4. As atmospheric CO2 increases, plant life comes back and further changes the planet albedo to absorb more energy. https://www.csiro.au/en/News/News-releases/2013/Deserts-greening-from-rising-CO2
5. Warming will continue as long as the sun is in a high output phase until the planet reaches a new equilibrium with its new albedo of heavy plant cover rather than ice.
So there you have it, a series of converging conditions that trigger the planet to go from “warm and wet” to “ice age” and back again.
What this means in the broader sense, not much. The conditions for both triggers completely ignore any sort of human intervention since they explain the natural changes from “warm and wet” to “ice age.” However we can assume that CO2 concentrations in the atmosphere will NOT prevent an ice age, and that high concentrations of CO2 in the atmosphere will NOT get the planet out of an ice age. With those conclusions, the concentration of CO2 in the atmosphere becomes less important than the overall planetary albedo, and the planetary albedo is something that humans have changed immensely due to construction, agriculture, and large scale engineering. This isn’t to say we shouldn’t worry about emissions, we should, just that we shouldn’t worry too much about CO2 at this point.
There are other opinions on the matter though: https://www.scientificamerican.com/article/sun-spots-and-climate-change/