The European Union’s climate policy chief, Frans Timmermans, has strongly backed the proposal.
The most challenging of them is around how to ensure there is no double-counting, in which both countries in a credits sale wind up claiming the emissions reductions toward their targets.
A second sticking point is around whether a small share of each transaction under the trading system should be levied into a fund for climate adaptation.
Yet another long-standing debate around Article 6, but one that appears closer to resolution, is around what to do with credits created under an abandoned past attempt at an international carbon trading market.
If negotiators are able to steer through all those issues, the hope is that the credit system will ultimately lead to greater collective emissions reduction than would otherwise be the case.