The whole passage here is causal. We can use similar diagramming that we would for sufficient/necessary to make life easy. Try not confuse it with conditional, but the idea is that the diagrams can still help.
Increase in level of atmospheric carbon -> atmosphere holds more heat -> causes more water to evaporate from the oceans -> increased rain -> washes some carbon from air into oceans -> becomes part of the seabed.
Decrease in level of atmospheric carbon -> atmosphere holds less heat -> causes less water to evaporate from the oceans -> decreased rain -> less carbon washed into oceans
This is more or less how I would diagram if I was forced to. But as you see, this is hugely time intensive. Better to focus on what you're reading and try to visualize this or write supper abbreviated versions. This question has a ton of causal layers making it tough time wise. But regardless here it is!
I hope this helps. Please let me know if you have any other questions!
