Humans tend to cut down trees and use the land for agriculture. This has been happening for thousands of years. Is this the real cause of global warming? Are gas guzzlers and coal power plants just salt in the wound, causing pain and blame? But the wound would still be fatal without them?

If this is the case, why is the world so focused on such pain and blame, and not focused on the real cause, and what to do about it? Can’t we somehow undo the effects of deforestation?

What would happen if every city and county were to plant hundreds or thousands of giant redwood trees? In WWII people had victory gardens. Why can’t we use the same principle as victory gardens to have clean air parks? Millions of parks around the world with land devoted to reversing global warming by consuming carbon dioxide and replacing it with oxygen? Whatever plants grow best in each climate and contribute the most oxygen.

Would this make sense? Or what don’t I understand?
"It’s a combination of causes" is clearly not a good answer, because it’s already known and assumed, and doesn’t even address the question. The question is not "what are the causes" but rather "what is the main cause" and "what can we do about that main cause".
Answers such as "emissions are a bigger cause than deforestation" need some kind of support or references, because, if they were obvious, the question would not be asked.
The answer posted by Nickel Johann giving the flowchart http://cait.wri.org/figures/World-FlowChart.jpg
is an eye-opener. If nobody can post any data to refute those figures, that answer is the most enlightening yet.
"If 90% of the planet would be forests and oceans" is an interesting hypothesis, but it seems to me it would imply a much lower world population, with a lot less industry and agriculture. But even with the same population and the same amount of pollution as now, would it really be correct? How much effect does each square mile of ocean have, vs each square mile of forest? If the amount of forest increased, but the oceans stayed the same, as they probably would no matter how much reforestation we did, and we kept reforesting till 90% of the planet’s surface was either ocean or forest, would that really not be enough to overcome our present carbon dioxide production?