(Reuters) -Californians were urged to ratchet down the use of electricity in their homes and businesses on Wednesday as a wave of extreme heat settles over much of the state, stretching tight power supplies to their breaking point. Temperatures in the most populous state are forecast to climb to well above 100 Fahrenheit (38 Celsius) during the afternoon. The extreme conditions are the latest sign of the impact of climate change in the U.S. West, where wildfires and severe drought have emerged as a growing threat. As spells of excessive heat become more frequent, the strain on power and water...