Human activity worldwide is now on such a planet-shaping scale that it resembles a geological process. A term has even been proposed for this phase of life on Earth: the Anthropocene.
The new epoch is challenging the rapidly developing field of Earth system science (ESS) to understand how our planet works as a single system, and how we are changing it.
Importantly, says Will Steffen, Emeritus Professor at the Australian National University's Fenner School of Environment and Society, it is also forcing us to question the direction we are taking, and to re-examine our relationship with the rest of the natural world.
"The concept of the Anthropocene is confronting to many people because it means we are in a new geological state of the Earth system," says Professor Steffen.
"The 'anthropo' at the beginning of the word suggests that this is the Age of Humans – which presents a lot of opportunities, but also some enormous challenges."
Our planet has existed in many physical states over the past 4.6 billion years, says Steffen, but we need to concentrate on what the conditions were like during the time that humans evolved. It turns out that the development of agriculture and the rise of all the great civilisations occurred within the past 10,000 years – a period of relative climate stability known as the Holocene.
As with those early human societies, our modern highly-globalised civilisation is designed to operate in the benign conditions of the Holocene. But now, the scientific evidence is mounting that human activity is profoundly affecting the Earth system itself, and pushing us out of the life-friendly envelope of the Holocene.
There has been a massive increase since 1950 in everything from global population and energy use to fertiliser consumption and international tourism – a phenomenon scientists call the Great Acceleration.
"A lot of economists would say 'this is progress. Look at how much more wealthy and connected we are'," says Steffen.
But, he says research data on a host of indicators, from ocean acidification and methane emissions to the loss of tropical forests and biosphere degradation, point to a wide range of significant global impacts to the Earth system after 1950.
Two things stand out about these indicators, says Steffen:
• They are all outside the Holocene limits of Earth stability.
• They don't represent a natural shift, but are the result of human pressure.
"The dilemma of the post-World War Two economic system we have built is that it is extremely good at making people wealthy, and at bringing people out of poverty, but it generates inequality and it misses a sustainable future. It puts too much pressure on the planet."
The current system is highly unstable with many internal incompatibilities, he says. It is shifting, and we don't know where it is going.
"Once you get an increase in temperature of more than of 2ºC you lose control. At that point, you can take emissions to zero and the Earth will not stop changing because of the intrinsic properties of the system," says Steffen.
Take that to 4ºC, and the results will likely be catastrophic, with scientists estimating that:
• Most of the tropics and subtropics will be too hot for human habitation.
• Most large agricultural zones may become unproductive.
• Sea-level rises of 20-40m are likely to drown coastal cities, agricultural areas, and infrastructure.
• Earth's maximum carrying capacity is likely to drop to 1 bn people or fewer (it is currently 7.4 bn).
In short, the difference between a 2ºC world and a 4ºC world, says Steffen, quoting climate scientist John Schellnhuber, is "human civilisation".
One of the drivers, globally, is overconsumption, he says.
"At least since the 1970s or 1980s we have somehow lost control over where our socio-economic system is actually taking us."
He says the idea of the Anthropocene "shakes people up" because it questions what we define as progress.
"Our biggest challenge is to reconnect to the biosphere."
Professor Will Steffen spoke at the Business School on 'Surviving the Anthropocene' in August, 2017, as part of the Dean's Distinguished Speaker Series.
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