And generally, the use of energy itself is a problem. Generating electricity adds heat to the Earth's system, or at the very best, moves heat from one place to another. Taken on a large scale, this alters climate patterns.
Instead of looking for cleaner sources of energy, we should be looking for ways to use far, far less energy. Converting to alternate energies costs a lot in terms of both money and resources (which then has other environmental impacts). Conserving energy can cause an immediate reduction in emissions without any investment of money or resources.