Two hundred years ago, humans numbered one billion. Now we are over seven billion and could reach nine billion by 2050. The scale and impact of the human species is now pushing the boundaries of Earth’s ecosystems, leading some scientists to recognise this as the age of humans – the Anthropocene.

Global changes in the Anthropocene have been extensive, multifaceted and rapid, challenging Earth’s biological and physical systems to survive and adapt to change. ‘Over the past 50 years, humans have changed ecosystems more rapidly and extensively than in any comparable period of time in human history’, says the UN Millennium Ecosystem Assessment (MEA) published in 2005.

We’ve cultivated one quarter of the Earth’s terrestrial surface, lost 20% of the world’s coral reefs and 35% of mangroves, quadrupled the volume of water impounded in dams and more than doubled the flow of the key plant nutrients, nitrogen and phosphorus. Such changes have undeniably changed the face of the Earth and contributed to a widespread and irreversible loss of biological diversity – the sixth major extinction event in Earth’s history, this time with humans as the cause.

Earth photographed from space.
This image is made from multiple photographs and data to construct the best approximation of what earth looks like from outer space. Most of the data came from MODIS on a satellite 700km above the surface. Taken Feb 8 2002. Image: NASA compsite

Why worry?

Ecosystems provide essential life-support services for humans valued at US$33 trillion globally, nearly double the gross world product. Yet fifteen of these services are in serious decline, says the UN, in particular fresh water, fisheries, air purification and the regulation of climate, natural hazards and pests.

The global Human Ecological Footprint, which measures the land and water needed to produce the resources we consume and assimilate the wastes we generate, has doubled since 1966. It equates to an unsustainable 150% of Earth’s renewable capacity, says the 2010 Living Planet Report.

Collectively, these changes are well outside any natural variability. Quite simply, we are causing the planet to move into a different mode of operation.

How much change can Earth’s various life-support systems withstand before they are irreversibly, and catastrophically, changed? Scientists believe three planetary boundaries – climate change, biodiversity loss and the global nitrogen cycle – have already been transgressed.

Surely the most serious threat of all is from anthropogenic climate change, with its dire scenarios for global warming, extreme weather, sea-level rise and oceanic acidification. Climate change scientists warn that if warming exceeds four degrees Centigrade, it will be ‘game over’ for life as we know it.

Tipping points and feedback loops would cause negative change to accelerate out of control, exceeding the ability of humans and natural systems to adapt in many parts of the world. That point stands to be reached before the end of the century.

Amazonian forest
A panorama image of the Amazonian forest from the top of the collection and research tower in Manaus, Brazil. Image: John Novis
© John Novis

The future

None of this is to deny the positive side to the Anthropocene. Guided by science and technology and driven by human creativity and energy, our exploitation of natural resources has led to massive socio-economic development. For many – but certainly not all – it has brought a dazzling array of benefits in knowledge, health, longevity, education, communications, mobility and entertainment.

Such advances are widely celebrated and are, understandably, sought by those in developing countries. ‘We live in the best of times and the worst of times’, concluded the UN Panel on Global Sustainability, with much of the world experiencing unprecedented prosperity, while the planet is under unprecedented stress.

Can we really expect to bring everyone in the growing population into the global middle class through the same resource-intensive development model pioneered by North America and Europe? To achieve today’s Western living standards, global economic output would need to grow by a factor of 60.

By 2050, a population of nine billion humans would consume between 180% and 220% of the Earth’s renewable biological capacity, says the World Wildlife Fund. In other words, we’d need the capacity of two Earths to provide resources and absorb wastes. The problem is, we only have one.

Planet under pressure

Can we usefully refer to the Anthropocene as a new epoch? Yes, said more than 3000 delegates to the Planet Under Pressure conference in London in 2012. The conference, attended by a further 3500 scientists online, aimed to assess the state of the planet and explore solutions to impending global crises.

Its key message warned that anthropogenic pressures are causing fundamental changes in the Earth system and moving us beyond safe natural boundaries. 'Humanity’s impact on Earth’s life support system has become comparable to planetary-scale geological processes such as ice ages’, it said. ‘Consensus is growing we have driven the planet into a new epoch, the Anthropocene, in which many of Earth’s system processes are now dominated by human activities.’

If the pre-eminent human goal is sustained quality survival, we must somehow adapt the human growth agenda that underlies the Anthropocene. For our survival we need new and sustainable values, behaviours, strategies and technologies.

Our challenge is to tame the Anthropocene tiger.

Dr Alan Jones, Senior Fellow, Australian Museum
This is an edited version of an article first published in Explore 34(4) pp 22-25.

Further reading

AD Barnosky et al., 2012. Approaching a state shift in Earth’s biosphere. Nature 486: 52–58.

Millenium Ecosystem Assessment, 2005. Ecosystems and Human Well-being: Biodiversity Synthesis. World Resources Institute, Washington, DC.

Planet Under Pressure Conference, 2012.

G Vince, 2011. An epoch debate. Science 334: 32–37.