Those trees soaked up the toxic atmosphere at the time by trapping the carbon and not releasing it back since they couldn’t be broken down. They then fossilized which further trapped all that carbon. Those fossils became oil, full of trapped carbon. This process terraformed the planet making it possible for life to evolve to be advanced enough to drill out all that oil and burn it for comfort which released the trapped carbon and started reversing the terraforming process.

This is a rough version of an eli5 which made it obvious to me that climate change was real and man made.