Only start producing and eating the optimal gruel as food. No more wasteful and useless things like coffee or fruit that isn't optimal for calorie-CO2.

Evaluate diet containing all micro and macronutrients with absolute minimum carbonfootprint and ban everything else. Enforce these bans harshly.

Stop producing meat, stop international flights, stop selling cars, stop producing clothes. That's the only way people will abide these policies. What's the point of saving the planet if you destroy your life?

As we have already seen this pandemic, you can't always guilt or shame people into action.