More trees and plant cover can help in the short term, but it's not going to solve the long term problem because those trees will break down and release the CO2 they've captured. This wasn't always the case as the ability for microbes and fungi to break down trees evolved later, which is how many of those coal deposits were created in the first place.

The main benefits from forest are habitats for wildlife, prevention of erosion, and ways to improve biodiversity. Their benefits to climate change are limited to reduced sunlight absorption because of their higher reflectivity and a small amount of a carbon sink if they take over land that was cleared and turned into plains, or farms or whatever.