I liked the response of one of the real climate scientists (as opposed to Gore's cosmetologist, landscape architects,
psychologists, lawyers, a philosopher, and a dermatologist) when asked if global warming is real. He said yes it has been warming up since the last ice age, but disagreed on the cause. In fact Dr. Schneider (one of only 5 of Gore's "scientist's" with training in climate, weather or other atmospheric sciences) in the 1970's was advocating global cooling and warning of a coming ice age.
The increases in green house gases in my life time is more due to the increase in people than industrial causes. When you consider each additional person generates as much CO2 as a hummer being driven 18,000 miles a year. However, more trees would help reduce the CO2 levels. The debate I have read though was if the old growth forests are doing as much good as a similar amount of new growth. IIRC there was some talk about the old growth being more static and not requiring as much CO2.