Why? An analogy I have seen is climate as a car speeding towards a cliff, and that waiting to get more data isn't enough. The suggested solution have been to remove the foot from the pedal and eventually the car will come to a halt. If I were to agree with the analogy I wouldn't just release the gas, I would hit the brake. That would be an active solution. Actively trying to prevent global warming by releasing chemicals that reverse the effect of greenhouse gases would be like braking.
The problem is that there is a political movement that is more concerned with reducing human impact on the environment than with actually saving it, they give fuel to the other side that doesn't care about the environment but just want the hippies to leave their back yard.
If people were really concerned about the environment then it would be irrelevant if global warming was man made or not, if a natural climate changed with lead to catastrophic consequences we would still have to do something about it.
Too bad the environment is not so discreet a system as your car. If we are brilliant at one thing, it is underestimating the unintended consequences of our actions. So no, let's not rush out an fill the air with pine forest vapor.