Why I am ready to go to war against the online lies being told about London

I’ve dedicated much of my decade as Mayor of London to cleaning up the capital’s air. But today, at the end of London’s Climate Action Week, I’m targeting a different kind of toxic pollution: disinformation.

In the last few months, I’ve been sounding the alarm about the vicious lies being spread about London on social media. I’ve taken on the rage-baiters who – aided by an army of bots and nativists – are deliberately painting a distorted picture of the capital as a lawless dystopia. And I’ve called out social media companies for designing algorithms that amplify the most extreme voices, feeding users a diet of content which keeps them feeling angry and alienated, without any concern for the harm it may cause.

The reason why the forces of fear, hatred and division are targeting London is obvious – they cannot stand the fact that a proudly diverse, liberal and progressive city like ours is flourishing because it flies in the face of everything they believe. It’s hardly surprising, then, that efforts to combat climate change – a cornerstone of progressive politics – have met the same response. Tackling climate change is being used as a proxy in this culture war.

When I announced my intention to expand London’s Ultra Low Emission Zone (Ulez), now the world’s largest clean air zone, it triggered one of the most sophisticated online disinformation campaigns in recent years, backed by at least $200,000 on X alone. We still have no idea who was behind the campaign, but we do know it was a direct challenge to our democracy.

Across social media, conspiracy theories proliferated about plans to create “climate lockdowns”, so the state could control citizens’ movements. One man, now convicted, went so far as to build a home-made bomb to destroy a Ulez camera near his home after being radicalised online, shattering the window frame in a child’s bedroom. Luckily, this appalling act of domestic terrorism did not have deadly consequences.

From outlandish claims about “15-minute cities” to ludicrous lies about wind turbines, climate disinformation is a booming business. The rise of AI has made it more profitable still, allowing almost anyone to create and disseminate climate disinformation in just a couple of clicks. Several of our greatest writers have observed that “a lie can run around the world before the truth has got its boots on”. Today, a lie can do a couple of laps around the globe before the truth has even woken up.

Disinformation is, of course, different from disagreement and debate. That distinction is crucial because we cannot pretend that the climate crisis is entirely beyond politics. The decisions we make about how to respond to our rapidly warming world will rightly provoke different opinions. In a healthy democracy, leaders shouldn’t just tolerate that debate – they should welcome it.

What they shouldn’t welcome, however, are systematic attempts to undermine the condition which makes that debate possible – the availability of reliable information. That is exactly what climate “wreckers” and their propagandists are seeking to do – rather than joining the conversation about how we respond to climate change, they want to destroy it by manufacturing doubt and denying the reality we face.

The scale of this crisis is shocking. New research published by C40 today shows that up to 48 per cent of online engagement on air quality and low-emission zones is being driven by bots. It’s no wonder, then, that three-quarters of Londoners think that disinformation poses a serious risk to their community. They are right to be worried. From fires and floods to deadly air pollution and disruption to our food and energy supplies, cities like London are on the frontline of the climate crisis.

By spreading confusion and tearing apart the consensus for climate action, disinformation doesn’t just make it harder to respond to crises in real time – it also threatens to leave us powerless to prevent global heating and public health emergencies in the years ahead. It is ordinary Londoners who will pay the price.

Fortunately, though, there’s a solution. Because cities aren’t just the first to face the consequences of the climate crisis – they’re also the first to fight back. With international negotiations stymied by deniers and delayers in recent decades, cities have been a beacon of hope. Now, faced with a dark blizzard of disinformation, the world is looking to us once again.

That’s why, today, we’re taking that fight a step further by setting up City Climate Facts – a new initiative, delivered by C40 cities, which will help cities around the world to understand, expose, and respond to online climate lies.

In London, we’ve already shown that we’ve got what it takes to win this fight. When we were deluged with disinformation about Ulez, we didn’t let ourselves drown. Instead, we doubled down. Faced with fabrications, we provided the facts – making our argument for cleaner air again and again. Almost three years after it was expanded, Ulez is now recognised around the world as a triumph of green, progressive public policy. It has reduced emissions and pollution. In 2025, we got the levels of nitrogen dioxide, one of the most toxic pollutants in our air, within legal limits almost two centuries before the experts said we would have without action.

But imagine where we’d be if we’d allowed disinformation to stop us. Rather than having fewer Londoners admitted to hospital with heart and breathing problems, as a recent study from Imperial College London has wonderfully shown, we’d have more Londoners falling sick and more children growing up with stunted lungs. When we talk about disinformation, we’re not talking about well-intentioned attempts to challenge, criticise or persuade. We’re talking about coordinated attempts to deceive, with deadly consequences – organised on online platforms where whipping up outrage earns you a profit, not a punishment.

In the fight against climate lies, the future of our planet isn’t the only thing at stake – the health of our citizens and the survival of our democracy are on the line, too. Taking a stand against disinformation is the only way to protect the welfare of our people and the freedoms they hold dear.

Sir Sadiq Khan is the Mayor of London and Co-Chair of C40, a climate leadership group comprising 96 of the world’s leading cities