about co2 levels in the air..., page-59

Wouldn't you say too much oxygen is more dangerous ???

The fossil record of fire first appears with the establishment of a land-based flora in the Middle Ordovician period, 470 million years ago,[11] permitting the accumulation of oxygen in the atmosphere as never before, as the new hordes of land plants pumped it out as a waste product. When this concentration rose above 13%, it permitted the possibility of wildfire. Wildfire is first recorded in the Late Silurian fossil record, 420 million years ago, by fossils of charcoalified plants.[12] Apart from a controversial gap in the Late Devonian, charcoal is present ever since.[12] The level of atmospheric oxygen is closely related to the prevalence of charcoal: clearly oxygen is the key factor in the abundance of wildfire.[13] Fire also became more abundant when grasses radiated and became the dominant component of many ecosystems, around 6 to 7 million years ago;[14] this kindling provided tinder which allowed for the more rapid spread of fire.[13] These widespread fires may have initiated a positive feedback process, whereby they produced a warmer, drier climate more conducive to fire.

http://en.wikipedia.org/wiki/Fire