Men and women are the "stewards" of the earth, not its "masters", Pope Francis said on Monday, recalling the theme of his acclaimed encyclical on the environment."We are stewards, not masters of our earth. Each of us has a personal responsibility to care for the precious gift of God’s creation," Francis tweeted.The Pope's nine-language @Pontifex account on Twitter has over 22 million followers.Environmental activists hailed the pontiff's environmental encyclical Laudati Si (Praise Be) published last June for its denunciation of the world’s fossil fuel-based economy and demand for greener energy sources.