FORT COLLINS, Colo. — This city takes pride in being green, from its official motto, "Where renewal is a way of life," to its Climate Wise energy program, which helps local businesses reduce the carbon emissions that scientists say can contribute to global warming.

But now two proposed energy projects are exposing the hard place that communities like this across the country are likely to confront in years to come as the tangled nuances of thinking globally come back to bite.