https://www.scientificamerican.com/article/as-temperatures-soar-during-heat-wave-so-will-co2/ > Greenhouse gas emissions will spike today as temperatures along the East Coast approach triple digits and grid operators fire up nearly all of their power plants to help Americans beat the heat. > The spike in emissions as temperatures rise is a characteristic of the nation’s electric grids. Many of the dirtiest coal- and oil-fired power plants sit idle for most of the year, because it doesn’t pay to run them. That changes on hot days. Residents and businesses turn on their air conditioners, pushing electric demand up and prompting grid operators to call on their seldom-used plants.