The Global Climate Action Summit: sub-national climate action explained

What was the Global Climate Action Summit?

The Global Climate Action Summit was a three-day gathering held in San Francisco in September 2018. Its guiding slogan was to "take ambition to the next level" — the idea being that governments alone were not moving fast enough, and that a coalition of states, cities, companies and campaigners could raise the pace of decarbonisation.

Rather than negotiating a treaty, the summit was designed as a showcase and a rallying point. Delegates announced fresh commitments on cutting emissions, phasing out coal, greening transport, protecting forests and mobilising finance. It was as much about momentum and signalling as about any single binding agreement.

The event drew participants from across the world — regional governors, mayors, chief executives, investors, scientists and non-governmental organisations — and ran alongside a busy programme of side events, exhibitions and public art across the city.

Why did it happen when it did?

The timing was no accident. The Paris Agreement had been adopted in 2015, committing countries to hold global warming well below 2 °C. In 2017, however, the United States announced its intention to withdraw from the accord, casting doubt over international cooperation.

In response, a broad movement of American states, cities and businesses declared that they were "still in" — that they would continue to honour the spirit of Paris regardless of federal policy. California, one of the world's largest economies in its own right, positioned itself at the head of that movement, and the summit became its flagship moment.

The message to the rest of the world was straightforward: even where a national government steps back, the economic and political weight of sub-national actors can keep climate ambition alive.

Who took part and what did they pledge?

The summit was convened by Jerry Brown, then Governor of California, and backed by a group of co-chairs drawn from business, philanthropy and international climate diplomacy. Participants spanned every continent and many sectors of the economy.

The commitments announced clustered around a handful of themes:

• cities and regions pledging to reach net-zero emissions and to run on clean electricity;
• companies committing to renewable power, electric vehicle fleets and cleaner supply chains;
• investors moving capital away from fossil fuels and towards low-carbon assets;
• coalitions to protect forests, restore land and cut short-lived climate pollutants.

No single pledge was legally binding in the way a national law is, but the cumulative signal was intended to reassure markets, encourage further national action and demonstrate that ambitious climate policy is compatible with a healthy economy.

The rise of sub-national climate action

The summit is best understood as one high point in a longer story: the growing role of "sub-national" and non-state actors in climate policy. Networks of cities and regions had been coordinating for years, sharing targets, data and best practice on everything from building standards to public transport.

This matters because a large share of global emissions is shaped by decisions taken locally — how cities are planned, how buildings are heated, how people travel and where electricity comes from. Local and regional governments often have direct control over exactly these levers, so their commitments can translate quickly into real-world change.

The approach is not a substitute for national and international policy, but a complement to it. When many cities and companies move in the same direction at once, they can lower the cost of clean technology, build political support and make bolder national targets easier to adopt later.

What it means for households and renewable energy

For most people, the practical legacy of gatherings like this shows up close to home: expanded cycling and public-transport networks, schemes to insulate housing, incentives for electric vehicles and heat pumps, and a steadily growing share of electricity from wind and solar.

Households can align with the same direction of travel through everyday choices. Switching to a green tariff, cutting waste and improving efficiency all reinforce the market signals that summits are designed to amplify. Our guide to renewable energy explains how green electricity tariffs work and what to look for.

If you want to explore how a cleaner, better-value energy plan could fit your home, our wider energy guides are a good place to start.

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