We are living in a new epoch of geological time – one of our own making. Human activity skews the chemistry of the atmosphere, oceans, and environment – rapidly and drastically. The Anthropocene describes this period of Earth’s history in which humans have started to significantly impact the planet’s climate and ecosystems.

The term Anthropocene (Anthropo meaning human) was first coined 20 years ago by atmospheric chemist, Paul Crutzen. He believed that, since the industrial revolution in 1750, we began to move away from the Holocene, the current epoch of stable climate that had lasted 11,700 years, beginning after the last major ice age.

There has been intense debate as to whether the Anthropocene should be officially designated as a new geologic epoch. To be classified as such, we must have changed the planet to the point that these changes are reflected in the rock strata. A working group of scientists within the International Commission on Stratigraphy, which oversees the official geologic time chart, voted to accept the idea in 2019 – meaning that we have indeed made this impact.

They examined socio-economic and Earth System trends (e.g. greenhouse gas emissions, climate, coastal zones, and biosphere integrity), all of which appear to have undergone a ‘Great Acceleration’ towards a hotter climate system and degraded, ill-functioning biosphere. The current rate of temperature and atmospheric carbon dioxide increase is almost unprecedented in Earth’s entire 4.5-billion-year geological history. The only other time temperature changed this dramatically was when an asteroid hit the area now known as the Yucatan peninsula in Mexico, 66 million years ago.

It all seemed to change from the mid-20^th century, the same time the first atomic-bomb blasts littered the planet with radioactive debris that became embedded in rock sediments. Will tells us Paul Crutzen had the right idea – just not the right timing.

But even now, ‘the Anthropocene is not stable,’ says Will. ‘It is trajecting away from the Holocene.’

While the Paris target aims to limit warming to 1.5°C, climate prediction models suggest that we will reach a warming of 3°C with our current trajectory – or, at worst, 4.5°C. The planet (and humanity) cannot handle change that fast. And once a certain point is reached, Earth’s systems will have been set in motion to all reach a cascading “tipping point” – and there will be no going back.

All of Earth’s systems are connected, leading to this cascade, like dominos falling down if one is knocked over. If the northern ice sheets melt, the influx of fresh water will destabilise the North Atlantic jet streams, a key part of global heat and salt transport by the ocean. This will in turn destabilise the West African monsoon, triggering drought, and reduce rainfall over the Amazon. It could also disrupt the East Asian monsoon and cause heat to build up in the Southern Ocean, which could accelerate Antarctic ice loss. Alarmingly, this is already happening.

Will warns that we are approaching a fork in the road, where our emissions and actions will determine Earth’s future. Whether we have a stabilised Earth or “hothouse” Earth is on us. While we might not even be the direct cause of the latter, according to Will, it might be us that pushes Earth over the edge of the tipping point.

Avoiding this tipping cascade requires fundamental changes to society. Equity problems need to be taken into consideration rather than swept under the carpet, given that there is a correlation between a country’s wealth and its contribution to pollution and carbon emissions. Working towards a more sustainable future requires not only advances in science and technology, but also more fundamental changes in societal structures and core values. Will suggests a move towards the Doughnut framework, which proposes an economy that supports the needs of people without overshooting the Earth’s ecological ceiling/boundaries. Ultimately, we should shift from a human-centric focus to a life-centric focus.

Aboriginal and Torres Strait Islander people have been already been doing this on these lands for over 65,000 years. They are the only surviving population to live through an ice age and the Holocene transition. They have developed traditions and ways of nurturing the land developed over millennia. Listening to and learning from Indigenous Australians might therefore show us the way forward towards a more life-centric society.

Evidence gathered by Will and others suggests that we are already in a state of planetary emergency. Humans are the only species on Earth that destroy their habitat – and we destroy it for other species too. We have to act now to avoid pushing Earth’s systems to their limit, or else ‘we might tip the whole planet’.

This article was prepared by Catriona Nguyen-Robertson, and follows a presentation to the Royal Society of Victoria on 8 April 2021 titled “The Anthropocene: Where on Earth are we going?” delivered by Professor Will Steffen (Australian National University).