Q1- What caused atmospheric CO2 concentrations to reliably increase by about 100 ppm in roughly 25,000 years for each (roughly) 100,000 year cycle?

Q2- What made CO2 concentration decrease over 50K to 75K years?

The answers to these questions are simple:

A1: Fires. Massive continent-scale fires...burning forests.

A2: Massive natural reforestation and weather. Yup. Hurricanes, cyclones, rain, etc.

While the idea of planting trillions of trees is excellent, we also have to understand an important point. The more trees we have the greater the probability of going backwards by decades when --not if-- a large fire rips through millions of them. We can't fight fires at those scales. And, if we could, you'd have to calculate the energy and CO2 we would produce in doing so (planes, trucks, equipment, etc.).

Climate change isn't an easy problem, not even close. I don't know if I want to laugh or cry when I hear politicians pushing some of the truly brain-dead stuff they get behind.

Thankfully some math has been done with regards to planting trees [1].

The next questions are:

How much suitable land is there and how many trees can it sustain?

How much water will they require?

Will they require chemicals (fertilizers, pest control, etc.)?

How much petroleum will they require? Keep in mind that oil is an inescapable part of most processes. An easy example of this would be transportation, tractors, cranes, packaging, etc.

Not being negative at all. Just want to make sure we all understand that without quantification anything sounds great.

As far as my investigation into this domain has revealed, yes, trees are the ONLY technology we have that stands a chance to do some good without making a larger mess in the process. The problem is that deployment at the planetary scale isn't easy. And there exists a real limit function on just how many trees you can actually plant around the world.

Not sure about your claim that trees can solve this problem in centuries.

Ideas like seeing the oceans with iron scare the hell out of me. Again, we are talking about planetary scale effects here. The energy and resources required for such a task are monumental. Beyond that, I don't know about you, but I've had plenty of experiences where an experiment was predicted to result in A and I we got Z instead. I cannot imagine doing something like that at a planetary scale. We could literally kill-off half the species in the ocean if we are not careful.

The most important thing we need today is to stop our politicians from spewing nonsense. Seriously. These people are dangerous beyond belief. It isn't only about none of their proposals being worth the paper they are not written on, they could actually cause massive harm and hamper real science-based approaches to making things better. In general terms, politicians have turned climate science into a disgusting circus act (or whatever analogy applies best). If you ask me, THAT is the most urgent task ahead for the scientific community: Getting politicians the hell away from this domain.

[1] https://e360.yale.edu/digest/planting-1-2-trillion-trees-cou...