Paris NDCs vs. Clean Air Act: The Real Regulation Update

Most people think new environmental regulation is the main lever for cutting emissions. That’s wrong. The biggest recent updates are not new laws but the ratcheting of existing frameworks—and the winner is the one with teeth. As practitioners, we’ve spent years watching how rules actually move the needle. The Clean Air Act’s track record shows what binding limits can do: between 1970 and 2020, combined U.S. emissions of six common pollutants dropped by 78 percent (EPA Progress Cleaning the Air). Meanwhile, global greenhouse gas emissions hit a record 57.7 gigatonnes of CO2 equivalent in 2024, up 2.3% from 2023 (OECD Climate Action Monitor 2025 / UNEP). That gap tells us voluntary pledges alone aren’t enough.

The contenders: three regulatory updates

When we advise clients on compliance strategy, we look at three live options: the Paris Agreement’s nationally determined contributions (NDCs), the U.S. Clean Air Act’s National Ambient Air Quality Standards (NAAQS), and the Montreal Protocol’s Kigali Amendment. Each represents a different regulatory model. Paris relies on voluntary five-year cycles. The Clean Air Act sets enforceable limits on specific pollutants. The Kigali Amendment phases down hydrofluorocarbons, a class of potent greenhouse gases. We judge them on four criteria: legal force, speed of implementation, scope of coverage, and political durability.

How they stack up on the criteria

Legal force matters most. Paris is a legally binding treaty—it entered into force on 4 November 2016, with 195 Parties (UN Climate Action: Paris Agreement). But its core commitments, the NDCs, are not binding. The Clean Air Act, by contrast, is codified at 42 U.S.C. §7401 et seq., and its NAAQS are enforceable. That’s why we’ve seen 91 percent improvement in sulfur dioxide concentrations between 1990 and 2020 (EPA Progress Cleaning the Air). The Kigali Amendment is binding on parties to the Montreal Protocol, which has been adjusted or amended six times since 1987. It’s a proven model: the ozone layer is well on its way to recovery thanks to global cooperation (UNEP OzonAction: Montreal Protocol).

Speed is another differentiator. Paris operates on a five-year ratchet, with the first global stocktake concluding at COP28 in 2023. That’s slow. The Clean Air Act’s deadlines, though often missed, force action: new coal-fired power plants typically install controls capturing up to 98 percent of sulfur dioxide and, in many cases, 90 percent of nitrogen oxides (EPA Progress Cleaning the Air). Kigali’s phase-down schedule is also binding but allows flexibility for developing countries. In practice, we see companies respond faster to enforceable limits than to voluntary pledges.

Scope differs. Paris covers all greenhouse gases economy-wide. The Clean Air Act regulates six criteria pollutants plus greenhouse gases, but its reach is limited to U.S. sources. Kigali targets a specific sector—refrigerants—but that sector’s emissions are significant. The Global Methane Pledge, launched at COP26, has over 100 countries representing 70 percent of the global economy and nearly half of global methane emissions, yet methane accounts for half of the 1.0°C warming over the past decade (US State Department: COP26 Global Methane Pledge). That’s a huge blind spot for Paris, which lacks sectoral mandates.

Political durability is the wild card. Paris survived the U.S. withdrawal under Trump, but NDCs are only as good as the governments that submit them. The Clean Air Act has been amended twice—in 1977 and 1990—and has weathered administrations. Kigali was ratified with bipartisan support in the U.S. Senate. But none are immune to political shifts. The OECD reports that only 30 countries and the EU, covering 17.7% of emissions, have enshrined net-zero targets in law (OECD Climate Action Monitor 2025 / UNEP). That’s a fragility we can’t ignore.

Who each option is for—and the winner

If you’re a multinational corporation with global operations, Paris’s NDC framework is your primary interface for climate policy, but it won’t force you to cut emissions quickly. If you operate in the U.S., the Clean Air Act is your daily reality—its NAAQS and MACT standards dictate your permits and technology choices. If you make refrigerants or HVAC equipment, Kigali is your binding constraint. For everyone else, the best move is to treat the Clean Air Act as the gold standard for enforceable regulation and push for Paris to adopt similar teeth. The numbers back this: under current policies, we’re headed for 2.8°C warming this century, far above the Paris goals (OECD Climate Action Monitor 2025 / UNEP). Voluntary pledges have delivered only a 14% collective reduction by 2030 versus 2022 levels, short of the 43% needed for 1.5°C (OECD Climate Action Monitor 2025 / UNEP).

We’ve seen this movie before. The Montreal Protocol succeeded because it had binding targets and trade sanctions. The Clean Air Act succeeded because EPA could sue polluters. Paris has neither. That’s why our recommendation is simple: prioritize regulatory updates that include enforceable limits, not just reporting requirements. The Kigali Amendment is a close second because it’s binding, but its narrow scope limits its impact. The Clean Air Act wins for its proven ability to cut emissions across multiple pollutants while surviving political change.

Bottom line

The single best move for practitioners is to advocate for binding, enforceable emissions limits modeled on the Clean Air Act, and to treat voluntary NDCs as a floor, not a ceiling. Until Paris gets teeth, we’ll keep missing the targets that matter.

Sources

• EPA Progress Cleaning the Air - https://www.epa.gov/clean-air-act-overview/progress-cleaning-air-and-improving-peoples-health
• OECD Climate Action Monitor 2025 / UNEP - https://www.oecd.org/en/publications/2025/11/the-climate-action-monitor-2025_aed0c4bb.html
• UN Climate Action: Paris Agreement - https://www.un.org/en/climatechange/paris-agreement
• UNEP OzonAction: Montreal Protocol - https://ozone.unep.org/treaties/montreal-protocol
• US State Department: COP26 Global Methane Pledge - https://2021-2025.state.gov/dipnote-u-s-department-of-state-official-blog/five_things_to_know_about_cop26/