I’ve been waiting for a ‘full-on climate crisis’ for 30 years. Now that it is getting due recognition, I am both scared and excited.

A bit of history will explain. When I first engaged with climate change after joining the environmental charity Greenpeace in 1989, I suffered from a common delusion: once the broader public understood the science, people would push for change, resisters would be won over and the world would set itself aright. I understood that this would require both pressure and persuasion.

So, after I became global head of Greenpeace in 1993, I encouraged direct action, such as the occupation of oil rigs. I also attended the World Economic Forum in Davos, Switzerland, to persuade corporate leaders to support change. I left Greenpeace to become an academic, consultant and businessman, but still clung to my delusion, especially after nations signed the Kyoto Protocol to cut greenhouse-gas emissions in 1997.

But as progress stalled and emissions kept rising, I looked at the evidence. When in history had a radical overhaul of global economy and society happened through worldwide consensus? Never.

In 2005, after I joined the faculty at the University of Cambridge’s Institute for Sustainability Leadership in the United Kingdom, I wrote to fellow climate advocates and laid out a more feasible path. I called it ‘Scream Crash Boom’. Many would scream about the threat, but society would not muster the necessary intensity until the crash hit. Then, people, governments and industry would respond with extraordinary speed — the boom.

Fast-forward to 2019: polar ice is melting faster than predicted, forests are burning like never before and extreme weather records are being smashed. This year, a team of serious scholars estimated a one‑in‑20 chance of a sea-level rise of 2 metres by 2100. Carbon dioxide levels are the highest they’ve been in human history. Already, there is widespread suffering, including tragic losses of human life and biodiversity, with poorer and marginalized communities the worst affected.

The climate emergency is now widely recognized. The UN secretary-general says we face a “direct existential threat”, and more than 1,000 jurisdictions in 19 countries have declared climate emergencies. Welcome to the crash.

Terrifying? Yes. But perhaps our best shot at action ever. Humans are slow to respond to threats, but can achieve amazing things when a problem almost overwhelms us. At that point, our willingness to sacrifice, to contribute to a larger cause and to tolerate strong government intervention can be remarkable.

Think how, during the Second World War, parents in UK cities sent millions of their children into the countryside, and complete strangers took them into their homes. Women were allowed to drive buses for the first time, and parks became farms. Scientists — for good and ill — stepped up. UK military spending went from roughly 3% pre-war to 52% of the gross domestic product in 1945. Days after the bombing of Pearl Harbor, the US car industry ceased production and transitioned to munitions manufacturing. In the 2008 financial crisis, governments rapidly nationalized financial institutions and mobilized trillions of dollars.

My critics would counter with stories of greed and thuggery after disaster, and of traitors and collaborators in war. Crises can also bring out the worst in some people.

But my reading of history suggests that this is not the dominant reaction. Humans can collectively connect and act during a crisis. This response has been studied well. It is sometimes referred to as disaster collectivism and has been attributed to the need to counter feelings of vulnerability and loss of control.

I’m confident that full-scale emergency mobilization to arrest the climate crisis is within our capacity, socially and practically, if we choose it. The planet’s young people are more energized than I’ve seen in my decades of activism. Many leaders, including Pope Francis, are calling for emergency mobilization. The Intergovernmental Panel on Climate Change has defined the requirements — and we have about ten years toget most of the job done.

In 2010, I published ‘The One Degree War Plan’ with climate strategist Jorgen Randers on the feasibility of emergency mobilization (J. Randers & P. Gilding J. Glob. Responsib.1, 170–188; 2010). It modelled cutting emissions by 50% in 5 years, reaching zero emissions within 20 years and capping warming to 1 °C above pre-industrial levels. I believe it is possible.

Such an emergency response is probably the best we could hope for. It could unleash innovation and investment at a global scale to deliver cleaner, more accessible energy, and spare millions of lives by reducing air pollution and military conflicts. We could expect more forests, cleaner seas and a healthier food supply. Shared adversity could build stronger, more unified communities.

Positive change is not inevitable — but neither is it pie in the sky. Potential economic, social and geopolitical benefits have been studied and defined. How we face this dire existential risk is our choice.

So, I welcome a declaration of climate emergency as an impetus for change, along with social movements such as The Climate Mobilization and Extinction Rebellion (both of which I have advised), and Swedish teenage activist Greta Thunberg’s school strikes. I can’t welcome the destructive burning of the Amazon, the melting of the ice caps or the devastating impacts already affecting many people around the globe. But I see their role in motivating greater action.

Now I urge you to breathe deeply, and join the emergency mobilization. We have work to do.