Mark Jacobson, Stanford University professor of civil and environmental engineering, lists the top energy sources, from best to worst:
The top electrical generating energy sources are:
- Wind
- Concentrated Solar Power (CSP)
- Geothermal power
- Tidal power
- Solar photovoltaics (PV)
- Wave power
- Hydroelectric power
- Nuclear power
- Coal (even with Carbon Capture and Sequestration, CCS)
Nuclear and coal actually tied for last place.
Read more from the Energy and Environmental Science Journal. For the non-academic, less-geeky version, Grist.org has a good summary.
Here's Jacobson discussing carbon dioxide: