On the other hand , any doubling of the percentage of carbon dioxide in the air would raise the temperature of the earth 's surface by 4 Â ; and if the carbon dioxide were increased fourfold , the temperature would rise by 8 Â '' . On the other hand , any doubling of the percentage of carbon dioxide in the air would raise the temperature of the earth 's surface by 4 Â ; and if the carbon dioxide were increased fourfold , the temperature would rise by 8 Â . ''