As mayors of two of the world’s great cities, we see every day how the climate emergency is already reshaping people’s lives, affecting the people and places we love. From deadly heatwaves and devastating floods to rising inequality and health crises driven by air pollution, the costs of inaction are not theoretical; they are measured in lives taken, homes destroyed andbusiness revenue lost.
Ten years ago, theParis agreementwas signed, marking a turning point in the global fight against climate breakdown. But today, progress is being undermined by a deeply concerning threat: asurge in climate deniersand delayers spreading virulent disinformation. We mustn’t let this hope disappear as the world gathers in Belém at the end of 2025 for Cop30.
This is not just a difference of political opinion or healthy debate. It is a coordinated, well-funded campaign to delay action, erode trust and protect the profits of the fossil fuel industry, which profits most from the status quo. These narratives find fertile ground on social media, where algorithms prioritise outrage over facts. They also thrive in moments of crisis and confusion, playing on existing frustrations among communities who don’t feel their voices are heard by those in charge.
In Paris, online disinformation campaigns have repeatedly targeted efforts to promote active travel, reduce air pollution by reducing car use and expand clean energy. These attacks don’t only come fromanonymous online accounts; they are often amplified by populist politicians and partisan influencers. As a result, policies designed to clean the air and protect public health have been distorted into culture war flashpoints.For example pedestrianising Seine’s riverbanks was opposed by powerful lobbies but the results talk for themselves: since 2011 air pollution from cars has been reduced by 40% in the city.
In London, the expansion of the ultra-low emission zone (Ulez), a policy proven tocut pollution and save lives, was relentlessly targeted by disinformation campaigns. These messages were seeded by anonymous accounts, supercharged by bots and then repeated across partisan media. The campaigns combined existing fears about the cost of living with more sinister and racially motivated tropes, leading to a surge in attacks onlineagainst politiciansand supporters,abuse of TfL staffdoing their jobs installing Ulez cameras, and eventually dangerous anddestructive acts of vandalism.
In the face of this tide of disinformation we will not be intimidated. Cities such asLondonand Paris continue to show that fair, fast climate action can improve daily life: making streets safer, air cleaner and homes more affordable to heat. But if we are to protect these gains, we must tackle climate disinformation by ensuring everyone understands and feels the benefits of these success stories.
That’s why, as leaders of C40 Cities and the Global Covenant of Mayors for Climate & Energy (GCoM), we are committing to tackle disinformation not just with facts but with fairer, better policies rooted in people’s everyday realities. We are building capacity across city networks to support trusted messengers, train local leaders and develop new tools to proactively counter misinformation. But we also need others to act.
We are calling on national governments, journalists, educators and tech companies to step up.
We welcome efforts such as the EU’s Digital Services Act, which requires online platforms to counter the spread of illegal content, including disinformation, and lays the groundwork for holding platforms accountable. But much more is needed. For example, the UK’s Online Safety Act could be strengthened by explicitly recognising climate disinformation as a form of harmful content.Social mediaplatforms are publishers and should be held accountable for hate speech and libel, as well as tackling the abuse of their platforms by anonymous bots giving a false impression of grassroots support.
We also need school leaders to ensure that media literacy and climate science are taught hand in hand, so the next generation is equipped to spot falsehoods and demand action. And we urge journalists and editors to prioritise evidence-based reporting on climate policy impacts, not just the politics surrounding them.
Disinformation flourishes when trust breaks down. Ultimately, fighting disinformation is not only a matter of public relations, it is about public leadership. We must rebuild the foundations of trust. That means listening to communities, addressing concerns head on, and showing through action that climate policy can improve lives today, not just decades from now.
The fightback against climate disinformation is gaining momentum. Brazil’s Cop30 presidency and the UN have made information integrity a top priority at the upcoming summit in Belém. Now it’s time for cities and national governments alike to lead.
Just as the last 10 years of climate action was forged by theParisagreement, the next decade will be defined by how well we protect the information systems upon which our democracies depend. To do this we must prove to everyone that the action we are taking is worth it. Cities are where that trust can be built.
Sadiq Khan is mayor of London and co-chair of C40 Cities. Anne Hidalgo is mayor of Paris, global ambassador for the Global Covenant of Mayors and vice-chair of C40 Cities