The National Renewable Energy Laboratory of the US Department of Energy has recently published a detailed harmonized lifecycle analysis of the greenhouse gas emissions of various energy sources. In summary, the results show that:

• all renewable and nuclear sources of energy supply except for the worst cases of biopower perform very significantly better than natural gas, oil, and coal.
• the range of possible emission scenarios for biopower, photovoltaics, and nuclear is greater than the range for concentrating solar, geothermal, hydro, ocean, and wind.
• the median of GHG emissions data for concentrating solar, hydro, ocean, and wind is significantly lower than that for biopower, photovoltaics, geothermal, and nuclear.
• post-combustion carbon capture and sequestration has the potential to bring total lifecycle GHG emissions within the upper 25th percent of the range of several renewable technologies.

Very detailed results are published in a number of locations with links at http://www.nrel.gov/analysis/sustain_lcah.html For a summary of results click on the Findings and Results link.