Despite two years of international diplomacy and two weeks of intensive negotiation, Glasgow’s COP26 summit was unlikely to be a decisive moment in the 25-year journey of UN-led climate change negotiations. Sure, positive steps have been made, and the negotiations didn’t collapse, a real threat at some previous COPs, such as Copenhagen in 2009. The mood in Glasgow was also lifted by a surprise US-China cooperation agreement which, while short of specifics and lacking the ambition of Washington and Beijing’s pre-Paris agreement in 2015, created more political space for a Glasgow deal. Nevertheless, even optimists must acknowledge that the event lacked the ambition needed to fulfil the promise of Paris six years ago, which set a cap on global warming of 1.5C above pre-industrial levels. Several key bodies, including the International Energy Agency, have said that if all the commitments announced wereimplemented in full — a huge “if” — global temperatures could be limited to just under 2C. However, Selwin Hart, the UN assistant secretary-general for climate change, has challenged such forecasts and asserted that the world is still on a “catastrophic” course to well over 2C. He highlighted a gloomy UN assessment of the 2030 picture, which indicates global emissions are on track to rise by 13.7 percent, a huge gap to bridge between today’s policies and action and long-term ambitions, and warned: “We cannot celebrate before we’ve done the job.” This confusing picture is one key reason why it is likely that there will be divergent views of COP26’sachievements. The only certainty is that there is no room for complacency, and the best that can perhaps be said is the event brought greater definition to the roadmap needed to keep 1.5C alive as the COP presidency baton is handed to Egypt in 2022 and the UAE in 2023. A fundamental question now is what needs to change to get even more traction, with the clock ticking toward what scientists warn are dangerous levels of climate change. After all, Egypt will not be able to mobilise the same diplomatic resources for COP27 as the UK did, despite the uneven commitment of Boris Johnson’s government. The answer is complex, but an increasing number in the international community perceive that there may now be a three-year window of opportunity, while President Joe Biden remains in office, to act in what he has called a decisive decade. After January 2025, when Biden’s term ends, the election of a Republican climate-skeptic president — possibly even Donald Trump — cannot be ruled out. Post-Glasgow, there is much needed to build irresistible momentum in future talks. This includes high levels of business engagement, which was one of the key themes of Glasgow. On Friday, for instance, the Investor Group on Climate Change — 733 major institutional investors worth more than $52 trillion dollars, more than half of all the assets under management globally — called on countries to go further with negotiating texts, including ending fossil fuel subsidies. This underlines that, ultimately, the world’s success in tackling climate change rests on deep, collaborative partnerships across the public and private sectors, with each challenging the other to deliver greater ambition. To enable this, greater clarity is needed on the post-Glasgow roadmap so that action can be taken, decisively and immediately, right across society. This highlights the critical importance — now, not decades later — of implementation after what is sometimes seen as a half dozen lost years of delivery after Paris. One of the key lessons of that period is that implementation of climate deals is best achieved through national laws as country emission commitments are most credible and durable if they are backed up by legislation. In the US, part of the reason Trump was able to unravel Barack Obama’s Paris ratification so easily is that it was politically impossible to have the treaty approved by Congress. Obama therefore embedded the agreement through executive order, which Trump rescinded, before Biden reinstated it. Compared to executive orders and other regulatory devices, legislation is more difficult to roll back. This is especially so when it is supported by well informed, cross-party politicians who can put in place a credible set of policies and measures to ensure effective implementation. While we are not yet close to meeting 1.5C, these domestic legal frameworks are potentially crucial building blocks to measure, report, verify and manage emissions. The ambition must now be that they are replicated in even more countries, and progressively ratcheted up, creating a global sustainability framework for billions across the world.