Excess heat from air conditioners raises outdoor temperatures at night by nearly 2 degrees F (1 degree C), worsening the urban heat island effect and increasing cooling demands, according to research from Arizona State University. Studying the Phoenix metropolitan area, researchers found that air conditioning systems pumped more waste heat into the air during the day, but the effect on near-surface temperatures was negligible. The same was not true for nighttime temperatures, however, when waste heat significantly boosts air temperatures because of nighttime atmospheric conditions. Air conditioning systems can consume more than 50 percent of total electricity during extreme heat, the researchers note, and summertime extreme-heat days are projected to become more frequent and intense as a result of climate change. Redirecting waste heat from air conditioning systems to household appliances such as water heaters, for example, could help alleviate the problem, the scientists say. They project that such strategies would save at least 1,200 to 1,300 megawatt-hours of energy per day in the Phoenix metropolitan area alone.