Why not reduce taxes for corporations building green tech? And provide R&D credit to pay the salaries of engineers working on the problem? Reduce capital gains taxes on investments in green tech? Make it easier for really smart immigrants to come to the US to work on the problem? Create a commission who's job is to review and simplify/eliminate/modernize regulations to reduce barriers to entry in the marketplace? etc.
There are lots of ways to incentivize industry to solve this problem instead of adding more taxes and hoping the government works as a good VC.
The Canadian government tried (and is trying) the angel investor/VC thing here and it hasn't worked at all well. They do stuff like matching investments of other angels or giving loans to entrepreneurs. I'd much rather they made it easier for me to start and run a company by reducing the stuff they are already doing instead of doing more things... like pretending they are private investors. For example, they recently announced a Startup Founder Visa which I think is a great idea and a step in the right direction: http://www.cic.gc.ca/english/immigrate/business/start-up/