Schwarzenegger signed another executive order on October 17, 2006 allowing California to work with the Northeast's Regional Greenhouse Gas Initiative. They plan to reduce carbon dioxide emissions by issuing a limited amount of carbon credits to each power plant in participating states. Any power plants that exceed emissions for the amount of carbon credits will have to purchase more credits to cover the difference. The plan took effect in 2009. In addition to using his political power to fight global warming, the governor has taken steps at his home to reduce his personal carbon footprint. Schwarzenegger has adapted one of his Hummers to run on hydrogen and another to run on biofuels. He has also installed solar panels to heat his home.