There is little novelty to be found in the Paris Climate Agreement. Nevertheless, it may have serious implications for climate policy-making. It establishes an international framework for decentralized climate policy-making by states, which should aim to achieve an ambitious collective objective of limiting global average temperature increase to well below to well below 2 °C or even 1.5 °C. The agreement does not set any mechanism, methodology or criteria, however, for assigning individual mitigation obligations to party states. It does not impose any significant substantive obligations on the parties, and, from a legal, as opposed to political or moral, viewpoint, it seems to be virtually non-binding. This gap is destined to become the Paris Agreement’s Trojan horse, because, under the guise of direct democracy in a system of multi-level, non-hierarchical governance, it grants not only credibility but also de facto authority to climate activists, thus posing a threat to constitutional government and representative democracy. The agreement demands that nation states explicitly acknowledge that their efforts are inadequate, while setting them up for failure, thereby changing the political environment in which climate policy is made. The ambition-obligation disparity creates a large arena for climate activism at international and national levels, effectuating a transfer of power, or at least of influence, that is inconsistent with the fundamental principles of constitutional government. If the collective efforts appear to fall short of achieving the Paris Agreement’s objectives, the judiciary is likely to be dragged into climate policy-making. Climate action groups or executive governments supporting ambitious action will charge the body politic with impotence, declare “government failure,” and seek the help of the courts to get governments to “do the right thing.” To support their claims, they can invoke the admissions and objectives set out in the Paris Agreement. Thus, in demanding that the signatories acknowledge explicitly that their efforts are inadequate, the Paris Agreement paves the way for the new international climate governance. Its implicit reliance on political activism by the climate movement and the related non-hierarchical governance by the courts constitute a threat to constitutional government, the rule of law, and representative democracy. It risks an unconstitutional usurpation of power by activist groups and unelected and unaccountable judges that could undermine legislative power and the role of positive law in deciding legal disputes. This risk of subversion is not well understood by politicians and governments. Nations should protect themselves against these threats. After all, signing away control over climate policy to unaccountable and unelected actors is not in the public interest. Nor is it, under even the most optimistic of circumstances, a viable path to rational, effective and sustainable climate policies. Indeed, the future of representative democracy may be at stake. Climate policy-making should not be left to the UNFCC secretariat, the climate movement and the judiciary. Now is the time for national legislatures to assert and defend their prerogatives.