The leading question of this paper is: Where does the normativity of the ethics of science and technology come from? This is a challenging question given that the traditional reservoirs of convenience (like metaphysical universalism) are no longer at our disposal the way they used to be. The paper is divided into eight sections: (1) It is specified what challenges a non-foundationalist justification and normativity has to meet. (2) A three-dimensional conception of responsibility is developed based on the human triangular (...) I–We–World relations. (3) The concepts of bounded responsibility and bounded ethics of science and technology are formulated. (4) The principle of reflective equilibrium is introduced as a principle of rationality, and it is shown how this principle generates rational and reasonable justifications in the ethics of science and technology. (5) Against this background, a reconception of internal and external responsibilities of science is given. (6) The type of responsibility demanded is exemplified by today’s climate research. (7) The paper argues for a hand-in-hand model of uncertainties in the sciences and for ethical obligations to preserve the conditions of human life on earth. The ethical argument is spelled out in terms of ethical care, preservation, and precaution. (8) Additionally, some arguments are developed to answer the question of why it is reasonable at all to preserve human life on earth. (shrink)