China will start a cap-and-trade system for carbon emissions.

This could be a big help in curbing global heating, or it might do nothing at all. A cap-and-trade system tends to be ineffective when the economy shrinks, and corruption can make it a no-op as happened in Europe.

By contrast, a tax on substances and activities that emit greenhouse gases is easier to enforce, and has its effect even if the economy shrinks.

Here's a proposal for a different way to do cap-and-trade, using a fixed total carbon emissions budget. Would that avoid the flaws? I don't know. But I think it is important to design the system so that the budget can be reduced.