Yeah, and while people like to say the rainforests are the "lungs of the world" it's actually the Siberian Taiga that contributes the most to O2 levels on Earth.
I read an article some time back, a science based one, that concluded that the Tunguska event (2000 Km^2) actually caused a measurable temperature blip. The effects of a burn off of this size will certainly pale those of the 1908 air-burst asteroid.