The scale of the effect we have on the planet is yet to sink in
Mike Sandiford
May 23, 2011
Surely it is inconceivable that human activity could rival the forces of nature. We are such insignificant creatures that it seems breathtakingly arrogant to believe our impact on the immense grandeur of our planet could be anything but minuscule.
That's what some prominent climate sceptics indignantly assert. Their incredulity may be understandable, but they are just plain wrong. Our species is now a geophysical agent of unprecedented power, albeit with unsustainable growth expectations.
Indeed, our impact is already so profound that my colleagues are seriously debating whether to christen this period ''the Anthropocene'' - a geological epoch dominated by the global effects of our own species.
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This is a timely reminder that humanity is not only altering the composition and dynamics of the atmosphere and the oceans but leaving its mark on the planet in many other ways.
Rivers and glaciers, for example, have moved about 10 billion tonnes of sediment from mountain to sea each year on average, over geological time. Each year humans mine about 7 billion tonnes of coal and 2.3 billion tonnes of iron ore. We shift about the same amount again of overburden to access these resources, along with construction aggregate and other excavations. In short, we are now one of the main agents shaping the earth's surface.
In Australia, natural erosion removes between 50 and 100 million tonnes each year. Yet one proposed mining development alone plans to extract about 14 billion tonnes of rock over a 40-year period, with peak extraction rates of about 400 million tonnes per year.
Our cities, transport routes, farms, forests and grazing activities have also altered the surface of more than half of all habitable ice-free lands. So rapidly are we extinguishing other species that future geologists will be able to discern this sudden mass disappearance from the fossil record - a mass extinction event seen only five times previously.
But it is in our energy use that the scale of our activity becomes truly mind-boggling.
Anyone who has seen film of a volcano erupt or those scenes of devastation from the recent Japanese earthquake and tsunami can intuitively appreciate the immense energy involved in the natural processes that shape our planet as it vents heat stored deep within its interior.
The rate at which heat is released from the earth - a measure of its natural ''metabolic'' rate - is about 44,000 billion watts, and reflects the average rate of energy used in moving all the continents, making all the mountains, the earthquakes and the volcanoes, in a process we call plate tectonics.
During the 20th century, it is estimated that a touch under 1000 billion tonnes of carbon dioxide was emitted from the burning of fossil fuels and cement production. Now we are adding about 30 billion tonnes a year and the rate of increase in carbon dioxide concentrations is doubling about every 30 years.
To generate all that CO2 we annually consume more than 13 billion tonnes of coal, oil and natural gas as part of a global energy system that operates at a rate of some 16,000 billion watts. The human consumption rate is already more than one-third of the earth's natural heat-loss rate.
And with our energy use doubling every 34 years, we are on course to surpass the energy released by plate tectonics by about 2060.
To put those figures in a more sober context, we now consume energy at a rate equivalent to detonating one Hiroshima bomb (60,000 billion joules) about every four seconds and are on a trajectory towards one Hiroshima bomb every second before the end of the century.
The ocean has already soaked up so much carbon dioxide that its acidity has increased by 25 per cent since pre-industrial times and, according to recent measurements, is now absorbing heat at a rate of about 300,000 billion watts. When my students measure the temperature in boreholes across Australia, they invariably see that as much heat is now going into the upper 30 to 50 metres of the earth's crust as is trying to get out - a result entirely consistent with the surface temperature rises measured by climate scientists.
The world's human population has grown so much and so fast - trebling in one century and still soaring by more than 70 million a year - that it is perhaps not surprising that the vast scale of our combined environmental impacts is yet to sink in.
Geologists don't readily tinker with their precious timescale - adding a new epoch is akin to adding a new verse to the Lord's Prayer. So proposing one named after us indicates that the international geological community fully understands the reality of the unprecedented impact we are having on our planet.
Mike Sandiford is professor of geology and director of the Melbourne Energy Institute, University of Melbourne.