With the demise of climate change legislation last year,
attention has shifted to the possibility of a patchwork of other
rules that would have the effect of cutting carbon dioxide
emissions. On the state level, one popular step is a renewable
energy standard for the electricity industry. Generally the
renewables standard is expressed as a percentage of the
electricity generated by all energy sources, often with
subquotas for solar power or geothermal energy. A few years ago,
there was talk of a national renewable energy standard, but in
his State of the Union address in January, President Obama
called for something slightly different — a “clean energy
standard,” with 80 percent of the nation’s electricity coming
from clean sources by 2035. “Clean” is a broader category than
“renewable,” but just what is it? Mr. Obama wants nuclear
energy, natural gas and “clean coal” — or plants that burn coal
more cleanly or use their technology to capture and store carbon
dioxide emissions — counted in the total. In March,