How do you know how much forest land there was when people thought the earth was flat?
Sounds like a load of **** to me.
There's certainly not more forest land now days, you only have to look at the rate that trees are being chopped down in South America and Asia.
That's why they invented catalytic converters, to convert the carbon monoxide to carbon dioxide. But that's not really the issue, the problem is more carbon dioxide is being produced than can be absorbed by the oceans/plant life/what ever else absorbs it.