In recent years the world has witnessed pandemics, conflicts, and economic downfalls. Climate change is to a considerable extent behind all these crises, and their increasing frequency and magnitude requires nations to act collaboratively and with greater ambition. Curbing greenhouse gas emissions is a necessity, requiring full implementation of commitments pledged by countries to the UN Convention on Climate Change under the Paris Agreement. Trickling down agreements into local regulations, it will be necessary to consider such gases as pollutants and control them—as with conventional air pollution enforcement. Through a half-century comparison with Brazil, this article describes how the United States is still a global benchmark for climate policies, despite the Supreme Court decision repealing the Clean Air Act. It shows expectations that greenhouse gases should become considered as criteria pollutants by the US Environmental Protection Agency. In particular, the Brazilian attempts to establish such provisions in its own territory can be considered as a means to gauge the effectiveness of the Paris Agreement from grassroots implementation. This study’s focus on regulating greenhouse gases certainly applies to many other democratic jurisdictions and opens a reflection on how to ensure that the global mean temperature goals can be achieved.