Carbon Dioxide 0.035%

I fully believe we coupld triple that number and it would have not catastrophic results. CO2 occurs naturally, and as it occurs naturally, there are things set up to naturally regulate its level.

Can anyone name me the single most devastating natural disaster over the past 20 years (since this global warming thing has aparently been kicked into high gear)? It was a Tsunami caused by an earthquake. Buy all the hybrid cars and cleaner gas you want, you're not gonna stop that. Tornados, Hurricanes, earthquakes, and extreme raining and drought periods have all been part of a natural cycle since the earth had a climate. Its not gonna stay the same temperature over the course of billions of years. During the time of the dinosaurs, there was no such thing as a polar ice cap. This has been proven by the finding of plant fossils in australia and antarctica that were around at approximately the same time.

Why is some water considered "fresh water" and some water considered "salt water" and how might the differences have come about?

During this time, the water reservoirs acted as sinks for the large amounts of carbon dioxide (as they do today) and through chemical and biological processes became locked up in sedimentary rocks as limestone. The nitrogen, which is not very chemically active continued to accumulate in the atmosphere. In addition, evidence exists that the Sun was stronger several billion years ago, strong enough to radiatively split (called photodissociation) water vapor molecules into hydrogen and oxygen. The hydrogen, being very light, escaped into space, while the heavier oxygen accumulated in the atmosphere.
These processes acting sequentially and simultaneously appear to have produced the delicate balance of 78% nitrogen (N2) and 21% oxygen (O2) we observe today.

There goes the theory that we're doing it directly, the theory that earth is closed off, and that we are even capable of dramatically altering our climate. It will rain, it will snow, and tornadoes will blow stuff around wether we like it or not.

As for gas becoming more expensive, they have found a new type of fossil fuel (ice hydrate, or something like that) that is noticeably more efficient in providing power but it also releases the devils breathe co2 Research is ongoing to find feasible ways to extract this fuel while we are continuing research on fusion which won't be perfected for nearly another 50 years. There's been research suggesting that mass will shift into a new phase around the end of 2012 (which would make any current living needs obsolete as we would then exist in a 4d grid with time being the 4th dimension or something like that) but it remains to be seen if its really going to happen or not.