Except that temperature was lowered because less sunlight reached the ground (and plants) due to particulate (soot, ash, etc) clouds that eventually settle putting an end to the effect. If temperature is raised due to excess CO2, the only way to change that is by reducing the CO2, of which the only way we know that won't use more energy (and produce more CO2) is through plants metabolizing it.
Besides, what happens if you compound human emissions with another enormous volcanic eruption? No one knows, things might cancel eachother out, or they might be far worse.