The government in Australia is going to start pricing carbon. If its like other markets the government creates they will just print as many carbon credits as they need or to hand out to their buddies. The least we could do is call their bluff and make it provably auditable by having a block chain.
What if a fork of bitcoin was created called carboncoin that you could use to buy trees to offset your carbon with ? Companies could trade them and this means the coins are backed by the need to offset emissions. This would need nurseries to accept the coins which they could then sell through a carboncoin exchange to companies. I know there are ways to buy carbon credits already so possibly you could also use that as the starting point when issuing coins ? Maybe the carboncoin exchange could sell those as well.
You might even buy them to offset your bitcoin mining emissions
carboncoin.org ? Just like bitcoin the .com was taken already....
I think this could ensure the market wasnt subject to the whims of corporations and governments but instead was decentralised.