The archaic and medieval practice of selling indulgences whereby sinners were assured that they would escape or evade purgatory was abolished by the Christian church in 1563.

When applied to the practice of selling carbon permits for the purpose of curbing carbon emission, it seems ludicrous. Yes, the environment is not ours to sell. And yes, allowing the indulgence of some but not all does not seem quite the "moral" practice. Although, this conceptual adaptation requires the action of environmentally destructive pollution to be "sinning," which is contentious, but I can accept. Where I do disagree, is in the labeling of the exercise of regulating carbon emission, (through a gradual, innovative and cost-effective method of cap-and-trade) as the allowance, through monetary payment, of monitored "sinning."

Had we allowed any of the seven deadly sins to become this destructive, would we simply dismiss the method of reducing their destructiveness because those of questionable (environmental) moral standing foolishly partisan the environmentalist community? (You can argue for the destructiveness of the other deadly sins if you like, but for the sake of argument, let's assume that the socioeconomic ramifications of climate change will be life-changing, to the point of resource war, mass famine, global instability).

Two "non-indulgent" alternatives:  

Voluntary market-mechanisms (VMMs) may propose "win-win" solutions at not cost to the social or economic infrastructure. It may bring previously uninvolved participants onto the environmental platform and it does increase peer influenced decision-making, which isn't always so bad. The major problems, which rule out VMMs as a pragmatic policy decision are: 

Foremost, the performance of "least-cost" upgrades. Corporations, Governments, or individuals who participate in these voluntary environmental programs make upgrades based on social status and market benefit. There is not fear of punishment or reparation.

Its ineffective targeting of affected areas does not create any incentive for major carbon-emitters to improve local conditions, leaving local communities to argue it's idiocy.

The other solution, command-and-control regulation, is far less practical in terms of creativity and progressive qualities. Yes command-and-control regulations establish a cap, is quick and effective, relatively unambiguous, and produces stable rule-enforcements. However, the problems should be obvious.

-Command-and-control regulations provide no incentive to advance green technologies, placing all the responsibility on government subsidies and private donors. 

-it relies solely on the power of the state and the accuracy of a newly established carbon register.

-It creates new, heedless bureaucracy. Not to mention, it would be very costly. 

Ok, so cap-and-trade:

C-and-T would be flexible. It would not conflict with capitalism or conflict with the way the state and global free-market economy have progressed (more appropriate- regressed) over the past decade. It would thrive on capitalism, and as we can already see evolving, create a global competition to develop renewable technologies. It would also install a cap on emissions, the same as command-and-control, but create incentive for polluting institutions to lower their emissions, as to increase profit revenues and punish those to pollute too much. Yes, it would create new bureaucracy, but far less than would be established under command-and-control, and through the punishment polluting institutions and the auction of carbon permits, a new source of revenue would be created. It can also target specific locales more effectively than voluntary market-mechanisms and would allow for marketed PR in specific polluting-institution locations. 

I would not consider this to be a purchase and sale of indulgences. If it is the most immediate and economically congruent method to save the planet, don't we have to adopt it?