With a career spanning 45 years, he has been engaged in environmental issues since the 1970s. He is the author of the "bible" of solar design, The Passive Solar Energy Book. Most significantly, he closed his practice in 2006 to start Architecture 2030, a nonprofit that challenges designers to achieve carbon neutrality in buildings by the year 2030. Carbon neutral buildings are ones that do not emit greenhouse gases or offset any emissions by producing renewable energy.