Here's my short list of stuff we don't know or can't explain at the present time, regarding earth climate/climate change.
1. The cycle of influence in the 65 Million year rotation of our solar system around the galaxy, and the "climate" we encounter in that cycle, due perhaps to our changing position in regard to large-scale variations in particle and radiative impacts on our upper atmosphere. We see an example of such impacts during our solar cycles, episodic variations in radiation and particle emissions, which we do correlate with weather changes on a 22-year cycle. The solar cycle is significant enough to require us to adapt our data somehow to remove that source of variation from our graphs and charts attempting to track greenhouse gas concentrations and climate.....but do we???/ nah. It just gets "too complicated" for inclusion, so we choose to ignore it. lol.
2. The cycle of internal changes in earth heat generation from nuclear physics. Lots of heavy stuff in the earth's molten core.... not just "Iron" really. Most of the heavy elements.... Uranium and Thorium for example. Well known fact that Uranium fission is impressively dependent on a chain reaction. We know we have plumes of hotter stuff coming up, melting their way up through the crust, all the time. We know we have epochs where volcanism and plate tectonics accelerate tremendously, interspersed with ages of calmer, slower action. We are in one of the slower phases, but are we getting hotter from increasing action? Nobody has even tried to answer that.
3. Stored crustal/oceanic heat fluxes. Non-atmospheric cycles of heat near the surface. To separate this from (2) above, let's just consider stores from atmospheric or ocean current action that convert to surface or near-surface heat. The big factor in play here, perhaps, is ocean temps at depth. During ice ages, the coldest, densest water (4C) actually settles to the bottoms of all our oceans, along with stuff like D2O or isotopically heavy water. That "layer" at depth actually is most of the volume of the ocean..... and most of the heat in the ocean. I mean, it's more heat per gram than what's in the ice shelfs off Antarctica.
I suspect our 100,000 year ice age cycle is the result, for the greater part, of this cycle. When our oceans begin to warm up at the end of the ice ages, there must be a corresponding change in atmospheric moisture.
4. Atmospheric moisture as a counter-cycle source acting in opposition to atmospheric carbon dioxide. Water in a heat sink for radiative energy, too.
During Ice ages, with cooler atmospheric temps assumed, there will be less humidity. Most ice sheets are precipitation deserts. Yes, it snows. But the water settled isn't any rainforest sort of gauge-rocker. The amount of water in the air is less than temperate values. Stores less heat. Ice shines white, the radiative inputs are radiated back out.... so things will stay cooler.... until something changes somewhere else. How will an Ice Age ever end???? Oceans at depth get colder, polar and elevated areas become ice mirrors.
What is the 100,000 cycle that tilts things back to warmer???
Well, ice on land is wetter than deserts. When enough land is covered it reaches a point where the ice and lakes begin to increase overall atmospheric humidity, and increase the heat retained in our lower atmosphere.
Well, enough for now.
