Mark Jacobson provides an excellent overview and ranking of carbon-reducing energy technologies from solar to nuclear by their potential to positively affect the climate and air quality, their land-use impact, and their ability to supply sufficient energy to meet global demand. There is also an online presentation available with some useful graphics which summarizes the results.
Here is the take-home point for those who don't wish to read the whole article:
In summary, the use of wind, CSP, geothermal, tidal, solar, wave, and hydroelectric to provide electricity for BEVs and HFCVs result in the most benefit and least impact among the options considered. Coal-CCS and nuclear provide less benefit with greater negative impacts. The biofuel options provide no certain benefit and result in significant negative impacts. Because sufficient clean natural resources (e.g., wind, sunlight, hot water, ocean energy, gravitational energy) exists to power all energy for the world, the results here suggest that the diversion of attention to the less efficient or non-efficient options represents an opportunity cost that delays solutions to climate and air pollution health problems.
and here are a few choice quotes:
Globally, about 1700 TW (14900 PWh per year) of solar power are theoretically available over land for PVs ... the capture of even 1% of this power would supply more than the world's power needs.
[W]ind resources off the shallow Atlantic coast could supply a significant portion of US electric power on its own.
Converting to corn-E85 could cause either no change in or increase CO2 emissions by up to 9.1% ... Converting to cellulosic-E85 could change CO2 emissions by +4.9 to −4.9% relative to gasoline.
[I]nvestment in an energy technology with a long time between planning and operation increases carbon dioxide and air pollutant emissions relative to a technology with a short time between planning and operation ... the delay permits the longer operation of higher-carbon emitting existing power generation, such as natural gas peaker plants or coal-fired power plants
(Via Gristmill.)