July 3, 2015
We can expect that those of a particular political persuasion will be quick to point out that Laudato si’ is not infallible teaching, which is, actually, true. “‘The Roman Pontiff, head of the college of bishops, enjoys this infallibility in virtue of his office, when, as supreme pastor and teacher of all the faithful - who confirms his brethren in the faith he proclaims by a definitive act a doctrine pertaining to faith or morals.... the infallibility promised to the Church is also present in the body of bishops when, together with Peter's successor, they exercise the supreme Magisterium,’ above all in an Ecumenical Council. When the Church through its supreme Magisterium proposes a doctrine ‘for belief as being divinely revealed,’ and as the teaching of Christ, the definitions ‘must be adhered to with the obedience of faith.’” (Catechism of the Catholic Church (CCC) §891)  Papal encyclicals do not, in and of themselves, have this infallibility. But that does not mean that the teachings of papal encyclicals can be disregarded by faithful Catholics.
This very question was addressed by the Second Vatican Council, which said in Lumen Gentium:
“In matters of faith and morals, the bishops speak in the name of Christ and the faithful are to accept their teaching and adhere to it with a religious assent. This religious submission of mind and will must be shown in a special way to the authentic magisterium of the Roman Pontiff, even when he is not speaking ex cathedra; that is, it must be shown in such a way that his supreme magisterium is acknowledged with reverence, the judgments made by him are sincerely adhered to, according to his manifest mind and will. His mind and will in the matter may be known either from the character of the documents, from his frequent repetition of the same doctrine, or from his manner of speaking.” 
This kind of teaching, while it is not arrived at by means of an “infallible definition,” and is not pronounced in a “‘definitive manner,’” is given divine assistance. (CCC §892) Thus, every Catholic is obligated to submit to it with “religious assent,” and sincere adherence. It is not to be responded to with a glib remark that the Holy Father should leave “‘leave science to the scientists.’” 
In Laudato si’, Pope Francis tells us that his Encyclical Letter “is now added to the body of the Church’s social teaching,” with the hope that it “can help us to acknowledge the appeal, immensity and urgency of the challenge we face.”  Faithful Catholics are not at liberty to reject it.