Adam said:

"The total amount needed is 3 billion tons, or 60 million per year over 50 years. In 100 years Mars would be warm, wet and have enough air-pressure to throw away the space-suits."

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I am skeptical about those numbers. I suspect there would be photochemical processes that would breakdown the C3F8 thus requiring a much larger amount. However assuming the numbers are correct, the requirement of 3 billion tons over 50 years means Mars would need to be colonized and have a significant industrial capability. This is a point that I've made more than once. Terraforming Mars logically follows colonization. There is almost no point in arguing about the method or ethics of terraforming Mars since terraformation is almost unavoidable after a self sustaining colony has been established (terraforming on Mars comes from "pollution"). There is actually a subtle issue about a colony NOT wanting to terraform the planet. Mars is very rich in iron. Most structures on Mars will be made out of steel. In the beginning there would be no reason to plate or coat steel structure because there would be no mechanism for oxidation (no free oxygen or liquid water). A structural engineer would certainly specify keeping the steel structure open and easily accessible so it could be inspected for cracks, x-rayed, magnafluxed, etc. Let 2 hundred years go by and the martian population built up to 100 million people with a supporting industrial structure made out of exposed steel. The atmospheric pressure has now risen to 20 millibars and liquid water becomes stable at room temperature. For the first time in the history of Mars, dew can form on the planet's surface. This dew is now forming and evaporating on the exposed steel structure that previously did not have an oxide layer (it's shiny steel). The colonists would now have a real problem because their entire infrastructure would begin to rust at the same rate from the same start time. This would probably be seen as a "bad thing".

Gary