We Homo sapiens got lucky. Very lucky. Back in the 1920s, when looking for a “safe” gas to use in refrigerators, chlorine was the element of choice in a new family of manmade chemical compounds – chlorofluorocarbons. In the 1970s, Paul Crutzen, Mario Molina and Sherwood Rowland discovered that while it was safe in our fridges, it was destroying the ozone layer, which is essential to protect all life on land.

Luck struck twice. Nasa scientists measuring ozone above Antarctica in the 1980s never saw the ozone hole in their data. Their computers were programmed to ignore any figures deemed “impossible”. Luckily, the British Antarctic Survey had no such technology and sounded the alarm. In 1987, nations signed the Montreal Protocol outlawing CFCs.

But here luck comes in threes. Bromine is as good as chlorine for fridges and air conditioners, but about 40 times more corrosive to ozone. And by mere chance, the industry chose chlorine as the global standard. If this had not happened, the ozone layer could have been ripped apart before we even knew it. In 1995, Crutzen, Molina and Rowland were awarded the Nobel prize in chemistry, obviously.

This story barely gets mentioned in the history books covering the 20th century, but it is a significant subplot in an emerging meta-narrative of our species. In this narrative, the most significant event in the last century was not the world wars, the Cold War, the Great Depression, civil rights, or the moon landings. It was when our species overtook the great forces of nature to become the most significant driver of change of Earth’s biosphere, the space where life exists.

It is this event that historians and geologists will be poring over for centuries to come. They will either wonder why, if this knowledge was known, did our species fail to act to prevent catastrophe after catastrophe – the tragedy of the global commons – or they will wonder how we found the political will and technology to navigate towards a safe and just future. The trajectory of our planet is in the balance. At the same time, ending poverty and ensuring there is food, clean water and energy for all are within our grasp.

Remarkably, 2015 is the make-or-break year and all the signs are there that we are changing course – a great transformation is not only within sight, it is under way. Here’s why. First, world leaders met in New York recently to agree the sustainable development goals – applying equally to all nations. This is a paradigm shift in thinking; it acknowledges for the first time that our wellbeing, the global economy and human development all rely on a stable biosphere and that this very stability is at risk. Second, we have reached “peak child”; the number of children in the world is no longer increasing. Population will eventually stabilise at 10-12 billion. And third, world leaders meet again next month to seek a workable solution to the climate challenge.

The best evidence from science indicates that there is still time to avoid dangerous climate change, but the window of opportunity is closing rapidly. The world’s biggest emitters – China and the US – are showing real global leadership for the first time. US leadership during the ozone crisis was critical to providing the necessary confidence to spark bold action by many nations.

But first, more drama: we can articulate precisely how high the stakes have become. Last week, we learned that the Earth had passed two new landmarks. Carbon dioxide in the atmosphere crossed the 400 parts per million threshold. The last time carbon dioxide levels were this high was at least three million years ago, before modern humans existed and in a very different climate to today’s. Scientists estimate that if we really wanted to safeguard a stable climate, then our limit should be around 350ppm.

The second landmark is linked directly to greenhouse gases. It was announced that the Earth’s temperature is 1C above pre-industrial levels. We are halfway to the 2C limit agreed by world leaders in 2009.

Emissions of greenhouse gases are changing the global carbon cycle. Damming, water extraction, irrigation and climate change are affecting the global water cycle. We use an area the size of South America to grow our crops and an area the size of Africa for our livestock. We move more sediment and rock than natural processes. Biodiversity is reaching mass extinction rates. There have only been five mass extinctions in Earth’s 4.6bn-year history; the last, 65m years ago, ended the reign of the dinosaurs. The oceans are becoming more acidic at a rate not seen for at least 55m years.

Don’t get me wrong. These changes have been remarkable for human wellbeing. Artificial fertilisers mean we can feed more people. Diseases are being eradicated on a global scale. We, in wealthy nations at least, live longer, healthier lives. But we have done this with a frontiers worldview – we have believed we can always expand and grow into new spaces to accommodate our needs. This is no longer tenable. We need to update our worldview: we are no longer a small world on a big planet. We are now a big world on a small planet.

The base upon which we have built all of this is a stable biosphere. As long as the Earth was relatively large, with good resilience and ample abundance of resource, we could benefit from subsidies from ample natural resources, a forgiving ecosystem and a stable climate. Ecosystems provide fresh water, pollination, fertile soil and food. Indeed, the stability of the global climate over the past 11,000 years, which geologists call the Holocene, has been the foundation for our global civilisation.

Mario Molina, left, and Sherwood Rowland, two of the four-person team that discovered CFCs’ effect on the atmosphere, in their California lab in 1976. Photograph: AP

In 2000, Paul Crutzen proposed that Earth has left the Holocene and had entered a new geological epoch, the Anthropocene, where humans dominate. This is not the result of some gradual transition over the 200,000 years since we emerged from the plains of Africa. We have hit the Earth like a comet. We became a phenomenal global force in a single lifetime – since around 1950, with most change happening in the last few decades.

The Anthropocene is up there with Copernicus’s heliocentricity or Darwin’s theory of evolution as one of the most profound shifts in worldview that has emerged from scientific endeavour. Since Crutzen’s remarkable intervention at a meeting of the International Geosphere-Biosphere Programme, the race has been on to answer one of the two biggest questions in science: if we are beyond Holocene boundaries, how stable is the Earth’s biosphere?

A tipping point is a scientific concept best captured by the idiom “the straw that broke the camel’s back”, or by the scene in Monty Python’s The Meaning of Life where a waiter places a “wafer-thin mint” in the mouth of a grossly obese man – Mr Creosote – who explodes. We know Earth has lurched across tipping points before, causing temperatures to change drastically in a matter of decades as the planet slips into a new regime. Given that the Holocene is the only state we know can support a population of 7.3 billion, a degree of caution would be advisable to avoid Mr Creosote’s fate.

While we are beginning to put together a picture of the Earth’s tipping points, the precise thresholds beyond which we risk irreversible change, deleterious for human societies, are as yet unknown.

Earlier this year, my colleagues and I published our latest assessment on the state of the biosphere and the parameters that must be safeguarded to remain within Holocene-like conditions. We confirmed our previous work, showing that there are nine planetary boundaries relating to, for example, ozone, fresh-water use, ocean acidification, new chemicals (such as CFCs) and aerosols – small particles in the atmosphere. We estimated that the Earth has crossed four boundaries as a result of human activity, relating to climate change, biodiversity loss, deforestation and fertiliser use. We are in a danger zone. If we cross one tipping point then we risk crossing them all.

So, we have reached the critical moment. What happens next is up to us.

But we are already seeing warning signs. With just a 1C rise in temperature, there are strong indications that some parts of Antarctica are destabilising. This probably commits us over the next centuries to another one metre sea level rise (in addition to the up to one metre sea level rise committed to over the coming century, according to most science), and which could be a prelude to a long-term sea level rise of six to seven metres if the trend of tipping points continue. If we burn all known reserves of fossil fuels, the Antarctic ice sheet will melt completely, causing a rise in sea level of around 58 metres. Given the implications, speculative drilling for oil in the Arctic may one day be seen as a crime against humanity.

Closer to home, climate change is implicated in Syria’s civil war. The unprecedented drought in 2007-10, which climate models indicate can be expected to be repeated in the region as greenhouse gases rise, led to a mass migration to cities, contributing to civil unrest and political instability.

If we carry on emitting greenhouse gases, then by the end of the century the world will be 4C warmer than just before the Industrial Revolution. This will be devastating in itself, but by that stage climate change may be difficult to stop and may trigger accelerated change. Hence the political consensus that going beyond 2C is “dangerous” and must be avoided. Setting such a planetary guard rail is critical, even though our scientific planetary boundary for climate change is set at 1.5C, showing that even 2C – a political “boundary” – is a risky threshold for humanity.

But after 21 years of trying, nations have yet to agree a global pact to avoid this fate. This is why, earlier this year, my colleagues and I published the Earth Statement, outlining the eight essential ingredients of a successful agreement in Paris. This has now been signed by business, political and religious leaders including Richard Branson, Arianna Huffington, Mary Robinson, Desmond Tutu, Al Gore and Paul Polman. In the weeks before the Paris summit, we have launched a social media campaign, This Is My #EarthStatement, to build public support. Instead of signing an online petition, people can sign their own bodies and post photographs online to show not just a strong message to politicians, but also personal commitment to act. We’ve seen enormous support from sports stars such as Olympic skier Julia Mancuso, musicians, business leaders and politicians – next week, 15 mayors from major capital cities will sign to show their support. Will the change be fast enough? Will emissions cuts be deep enough?

So to the other most important question in science: how can societies transform? Science is good at solving constrained problems, such as “what is the structure of DNA?” or “how do you land on the moon?” Or even “what are the Holocene boundaries?”. It is less good at “wicked” problems, such as poverty and overpopulation. In the Anthropocene, we have “super wicked” problems (first identified by Kelly Levin, Benjamin Cashore, Graeme Auld and Steven Bernstein), where time is running out, there is no central control and the people attempting to solve the problem caused it in the first place .



In this environment, transformation emerges when worldviews change (science can be a good driver here), when new goals are set, when rules are introduced (and enforced), when the flow of information changes and when confidence reaches a threshold and spreads throughout the network like wildfire. I believe the building blocks are in place.

The shift in worldview is represented by the Anthropocene. After the largest consultation in the history of the UN, the sustainable development goals provide the new compass point. The planetary boundaries framework is a mind-shift in the relationship between people and planet and a first attempt to set some rules to minimise risk. Information flows have altered radically since the internet revolution. Three billion people have access to the internet and there are 7bn mobile phone subscriptions. In the next decade, this will explode further.

Skier Julia Mancuso is one of the celebrity supporters of the #EarthStatement campaign. Photograph: The Earth Statement

The priorities of the UN goals are clear and aligned with science – end poverty, decarbonise the global economy, halt biodiversity loss and protect the remaining forests on Earth. We need nothing less than a new industrial revolution for rapid transformation. Incremental change is not enough.

Moore’s Law describes how computer processor speeds double every two years. The entire industry is now built on this foundation – and this changes how companies operate. We need a Moore’s Law for global sustainability. We need to get on a curve where entire sectors of the economy will change radically in the next few decades. If global sustainability becomes the compass point for a million hi-tech entrepreneurs and developers from Bangalore to Tokyo to Silicon Valley and Stockholm, then this industry alone will put a significant dent in the universe, to paraphrase Steve Jobs.

But technology is not enough. Policy support is essential. We need to decarbonise the global economy by 2050 and run on 100% clean energy. We need a price on carbon. We need to keep within a carbon budget of one trillion tonnes of carbon dioxide – or 27 years at current emissions rates. We need a $100bn-a-year investment in sustainable energy systems for rapidly developing countries. We need to invest in adaptation to the change that is now inevitable. And we need 193 nations to unite. These are the foundational principles of the Earth Statement.

And here is the good news. The transformation is under way. Copenhagen has announced it will be free of fossil fuels by 2025. Now Sweden is seriously talking about being the first fossil-fuel-free country. I believe it could do this as early as 2030. Imagine the signal this will send. Germany aims to decarbonise the world’s fourth largest economy without relying on nuclear power. The UK has a climate law legally binding the country to 80% emission reductions by 2050.

Now let’s return to Paul Crutzen. The Dutch chemist was one of the founders of the International Geosphere-Biosphere Programme, set up in 1987 to coordinate research internationally on global change. The findings that emerged from this research are changing how we think about our relationship with the planet, not least during the Anthropocene. It has had a seminal influence on the creation of a new academic discipline: Earth systems science. After almost 30 years of operation, it closes this year.

In its place, we need a new research programme – a global endeavour with the vision of the Apollo missions – to ensure the stability of Earth’s biosphere. Or, to quote Mark Watney (Matt Damon) in The Martian, we need to “science the shit out of this”. This will require a new type of science to support the transformation of societies, one that brings together climate researchers and Earth systems scientists with economists, behavioural scientists, ecologists, health specialists, engineers and many more. It must also engage business, policymakers and the public in a new way. Unlike Watley, no single country can do this alone.

The international research programme developed to support this is called Future Earth, which meets in Japan this week. It is bringing together the world’s leading intellectual might to tackle the greatest scientific challenge of our time and it needs the support of all nations.

Johan Rockström is a professor in environmental science at Stockholm University and executive director of Stockholm Resilience Centre