Guy Stewart Callendar (/ˈkæləndər/; 9 Fabrairu 1898 - 3 Oktoba 1964) ya kasance injiniyan tururi na Ingila kuma mai kirkiro.[1] Babban gudummawar sa ga ilimin ɗan adam shine haɓaka ka'idar da ta haɗa haɓaka carbon dioxide a cikin yanayi zuwa zafin jiki na duniya. A cikin 1938, shine na farko daya nuna cewa zafin ƙasa na Duniya yatashi a cikin shekaru 50 da suka gabata.[2] Wannan ka'idar, wanda Svante Arrhenius ya gabatar a baya, an kira shi tasirin Callendar. Callendar yayi tunanin cewa wannan dumama zai zama mai fa'ida, yana jinkirta "komawar mummunan kankara".