We propose a novel macrofinance model for the EU area comprising both climate damages and an Emission Trading System that interacts with credit markets with a bias for 'net-zero' brown firms and opaque voluntary carbon credit markets. Our model suggests that the implied allocation is far from the first-best. Relevant welfare gains can be obtained in a setting in which a Green Coin Central Bank (GCCB) runs a transparent blockchain in which coins are mined after a decentralized verification of private offsets, and the GCCB manages green coin prices through open market operations.