b'THREEThe pope uses his papal authority to address ecology.Pope Francis addresses ecology with one of the most authoritative means of papal teaching authorityan encyclicalto date. 1This is especially so with his treatment of climate science, wherein he recognizes that a very solid scientific consensus indicates that we are presently witnessing a disturbing warming of the climatic system (LS 23) and invokes the precautionary principle:If objective information suggests that serious and irreversible damage may result, a project should be halted or modified, even in the absence of indisputable proof. Here the burden of proof is effectively reversed, since in such cases objective and conclusive demonstrations will have to be brought forward to demonstrate that the proposed activity will not cause serious harm to the environment or to those who inhabit it. (LS 186)He has done this at a critical moment in history as the world faces the prospect of runaway, effectively irreversible climate change. Timing is everything, and Pope Franciss choice to address ecology in his first major encyclical signals to all people of faith and goodwill the gravity with which he views present environmental challenges. 2ARTICLE 9'