aggressively stimulating renewables is one thing, but a lot of people are calling for a world wide flat carbon tax. That is a very regressive tax that will hit the poorest the hardest. It will barely register for the average californian, but it will cause many products and services to be priced out of reach from people in developing economies.
So the worst case scenario all depends on what is being proposed.
The "regressive" part of the tax can be mitigated just by rebating some (most?) of the money back to the people who would be most impacted. The rest can be used for R&D into clean energy, power grid improvements, etc.
The bigger issue is making sure the tax is applied consistently everywhere, otherwise we just move polluting industries to countries with lax enforcement and put countries that are enforcing the tax at a disadvantage.
So the worst case scenario all depends on what is being proposed.