B.C. Hydro—one of North America’s greatest champions of compact fluorescent light bulbs—has discovered an “unintended consequence” in their increased use. The cool-burning bulbs have resulted in a substantial decrease in electricity use. But unlike inefficient incandescent bulbs, which give off excess heat, CF bulbs don’t help warm the house . . . so people turn up the thermostat. The result, B.C. Hydro estimates, will be a 45,000 tonne annual increase in greenhouse gas emissions by 2017.