How much does reforestation actually help?

According to an article in ScienceDaily entitled "Agricultural Methods of Early Civilization May Have Altered Global Climate," recent generations are not completely to blame for Earth's climate heading in a downward spiral. The slash and burn method used in early civilization was used to clear large plots of land for farming. This method was counter-effective in many ways. First of all, large amount of carbon was being emitted into the atmosphere which, as we know today, diminishes the quality of air as well as the overall well-being of the environment. Secondly, the amount of crops being grown on these huge plots of land is incomparable to the amount of people we can support on significantly smaller plots in today's world. Lastly, they did not realize that as population grew and new land became scarce they would have to change their methods.
Despite these troubles, which for the most part we have overcome, forests have been growing back in areas which have previously been burned down. We as a globe have been trying to reverse the consequences of our actions as well as the actions of generations before us. We have been making strides to grow more trees and keep more forested land to reverse the excess carbon in our atmosphere. What we have a problem realizing is the fact that we are going against our own efforts with the amount of fossil fuels being burned every day in all parts of the world. As a globe, we are completely dependent on fossil fuels and are emitting an irreversible amount of carbon and other harmful gases into our environment. We need to come up with cheap and more efficient ways to produce energy before we reach a self-inflicted rock bottom.
http://www.sciencedaily.com/releases/2009/08/090817073502.htm