Human beings are now up there with the ice ages, comet impacts and volcanic super-eruptions in driving impacts on the environment on a global scale, according to one of the world's leading experts on global warming.

Will Steffen, Director of the Australian National University's Fenner School of Environment and Society, says societies are now at a crossroads and need to take urgent action to repair and protect our "life support system".
"Even though we know global environmental stresses are increasing, we can't seem to turn them around," says Professor Steffen, a former executive director of the 80-nation-strong International Geosphere-Biosphere Programme. "We are pushing the Earth into planetary terra incognita."

We now rival the great forces of nature in our impact, he will tell the Australian Academy of Science's Dangerous Climate Change symposium in Canberra on Friday (9 May 2008). And most of the impact has occurred over just the past six decades.

He wants to see a new epoch - the Anthropocene - added to the geological timescale to reflect the scale of human impact since the industrial revolution. Powered by fossil fuel, industrialisation from about 1800 saw for the first time our species affecting the Earth System on a global scale. Pre-industrial effects had been confined to regions or continents.

Professor Steffen and colleagues, Paul Crutzen - winner of the 1995 Nobel Prize in chemistry for research into the ozone layer - and historian John McNeill, of Georgetown University in the US, have tracked the progress of the Anthropocene using atmospheric carbon dioxide levels as an indicator. They published their results in the journal Ambio.

They say the second stage of the proposed Anthropocene epoch - the great acceleration - started in the post-war era from 1945 when the global economy boomed. Carbon dioxide levels have surged to 385 parts per million today against 319 ppm in 1950 and a preindustrial value of about 275 ppm.

"About half the rise since the pre-industrial era occurred in the past 30 years," Professor Steffen says. And judging from greenhouse gas levels, human activity might now be swamping the natural ice age cycles.
He agrees with Griffith University researcher and Australian Conservation Foundation president Professor Ian Lowe that it is time to give the environment priority in the "triple bottom line mantra", which calls for a balance between economic and social as well as environmental factors.

"The triple bottom line doesn't apply at the global scale," Professor Steffen says. "It is in fact a hierarchy. At that scale our own life support system is fundamentally important. If the Earth's environment becomes much less amenable for human life, it's impossible to have a viable society or a thriving economy."

Humanities scholars need to have a bigger input into the greenhouse debate to "examine our core values", he says. "How society responds will make the difference between sustainability and collapse."