There won't be a carbon tax in Germany. People are allergic to anything that has tax in the name. Instead Angela Merkel has chosen to strengthen the CO2 certificate trade in Germany which is known to be ineffective by design [0]. So if international carbon trading doesn't work either then that means there is no effective policy that will allow us to reach our CO2 goals.

The only hope that we have left is that speculative investors drive up the price. The more middlemen the better. If everyone bought 100€ worth of certificates every year and only sold when the price goes up it and keep them forever if the price goes down then this would at least simulate the effects of a CO2 tax because the effects would ripple through the entire economy without requiring action from politicians.

Paying directly for your own carbon sequestration doesn't work because it only has local effects, doesn't encourage prevention of emissions and it is effectively a letter of indulgence ("I'm free of my sin").

[0] many sectors are exempt, a base amount of certificates is handed out for free, the price is always low because there are too many CO2 certificates