In diplomacy and governing, there are few permanent victories, mostly hard-fought opportunities to make continued progress with continued attention. I often think of Benjamin Franklin’s comment to a young citizen after the delegates finished drafting the Constitution in Philadelphia, promising that they had created “a republic, if you can keep it.” After COP26, something similar could be said for climate diplomacy: It was an important breakthrough, if we can follow through on it.

A gap remains between the ambition the world...

Delegates negotiate ahead of COP26, the U.N. Climate Change Conference in Glasgow, Nov. 13.

Photo: Christoph Soeder/Zuma Press

In diplomacy and governing, there are few permanent victories, mostly hard-fought opportunities to make continued progress with continued attention. I often think of Benjamin Franklin’s comment to a young citizen after the delegates finished drafting the Constitution in Philadelphia, promising that they had created “a republic, if you can keep it.” After COP26, something similar could be said for climate diplomacy: It was an important breakthrough, if we can follow through on it.

A gap remains between the ambition the world demonstrated at the climate conference in Glasgow and the actions we need to take to avoid chaos by limiting the Earth’s temperature increase to 1.5 degrees Celsius above pre-industrial levels. The outcome of COP26 kept the ability to avoid that disaster within reach. At the climate conference, the world finally brought together the coalition we need to win this fight, not only almost 200 governments but the private sector, large organizations, tribal and indigenous communities, and young people. With continued cooperation across this alliance, we are entering the decisive decade of our climate battle prepared for the fight.

The Glasgow Climate Pact sends a clear signal that the world intends to win it. After years of negotiations, we finally finished the backbone of the Paris Agreement. The implementation “rulebook” attendees agreed to will guide global cooperation, ensuring transparent reporting and aligned emissions timing targets the market has needed and environmental advocates have long sought. The pact’s text also took unprecedented steps by recognizing the need to reduce global carbon-dioxide emissions at least 45% by 2030 so we can reach a net-zero, pollution-free world by midcentury. It included the first-ever calls from a climate agreement to phase down unabated coal and eliminate wasteful fossil-fuel subsidies.

This climate agreement also called for a doubling of the funding commitment to help developing countries adapt to a warmer world, many of which have caused little of the problem but whose people stand to suffer some of its worst consequences.

Perhaps most important, at COP26 we reached a newfound global consensus to take wide-reaching action to protect the Earth. Starting this year natural treasures and forests will be better protected. Waters and ecosystems will be healthier. Agriculture will be more resilient. The world will be less polluted and closer to environmental justice.

At his global virtual summit in April, President Biden laid out ambitious new U.S. climate commitments and challenged others to follow suit by the time we met at Glasgow. As of the close of the conference, countries representing 65% of the world’s economic output are committed to specific actions to hold global temperatures’ rise below 1.5 degrees Celsius. Even nations that have traditionally been skeptics announced plans to deploy renewable energy and move away from fossil fuels. In the months leading up to COP26, India pledged to deploy 450 gigawatts of renewable energy. Other large economies, including Indonesia, South Africa and Mexico, are prepared to reduce coal or oil dependency providing they can get help with finance and technology. This summer, Saudi Arabia announced an enormous and potentially game-changing plan for a transition into the renewable energy market.

The world saw enormous progress on cutting emissions of methane, a greenhouse gas up to 80 times as destructive as carbon dioxide—the single fastest step to slow global warming. In the runup to the conference, President Biden and European Commission President Ursula von der Leyen announced a global pledge to reduce methane emissions by 30% by 2030, and more than 100 nations representing 70% of the world economy quickly signed on.

Methane was at the core of a significant breakthrough between the U.S. and China at Glasgow. By next year, China agreed to develop a comprehensive and ambitious plan to reduce methane and make best efforts to accelerate the phase-down of coal. Our nations have no shortage of differences, but we must cooperate to solve our climate challenge.

All elements of the COP26 coalition will have to work together to stave off global warming. No government can fully fund the trillions of dollars necessary to make the transition to clean energy. To reach that goal, we need the private sector. Half of the emissions reductions the world needs to keep temperatures’ rise below 1.5 degrees Celsius will have to come from technologies not yet on the market. This is why President Biden launched the First Movers Coalition of companies, including Amazon, Apple

and United Airlines at Glasgow. The firms placed some of the first orders for zero-carbon ships, green steel, and 85% cleaner jet fuel, accelerating demand in these potentially multitrillion-dollar new industries. Banks and asset owners with trillions under management came to COP26 committed to accelerating and investing in this transition.

Add it up, and we have assembled both the team and tactics necessary to beat climate change. Now we all have a choice. We can bemoan that there still exists a gap between the world’s climate ambitions and its concrete commitments, or we can work ferociously to close them. It’s not too late to avoid the worst of a climate crisis. The International Energy Agency tells us that if every one of the Glasgow commitments are fully kept and implemented, it could hold global warming at 1.8 degrees by the end of the century. That’s not 1.5, but it’s progress—if we can keep it.

Mr. Kerry is special presidential envoy for climate. He served as a U.S. senator from Massachusetts (1985-2013) and secretary of state (2013-17).

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