quote: Carbon monoxide, not dioxide. It's toxic to humans and animals. Its the leading cause of death by air pollution, and its produced in engine exhaust, along with C02 and heaps of other compounds.
quote: You're right, but it's very unlikely that organisms of today (including many food crops) would be able to survive such conditions, as a result of the millions of years of evolution that have taken place. Also, the higher temperatures would melt the ice caps, leading to sea level rise.
quote: It's both. A imbalanced diet is bad for you, so too is an excess of anything. Vitamin A is essential to the body, but only in minute quantities. Too much leads to death.
quote: Equilibrium isn't; constant though. It can occur over long timescales, but if the balance is shifted over a short period of time then the results can be very violent or unpredictable. Massive hurricanes, solar storms and other natural phenomena are an example of this.