How Cap and Trade is Like Prior Appropriation Rights

An article about the proposed carbon dioxide cap and trade system compares the process for allocating emission permits to prior users to the prior appriopriation water rights scheme that most Western states have adopted:

"Water is a finite quantity, so the cap is often set by nature rather than by a political body, but the effect is the same. In the same way that some people gained the right to withdraw water from a river or lake based on their past use, power companies under the sulfur program gained the right to emit sulfur based on their past emissions. If one views the right to emit gases into the air as a resource such as water, there is little difference between the two cases."