Ever since humans emerged onto the wild savannah, we have modified our environment -- burning our way through forest, cutting necklaces of rice into mountains, shifting rivers, hunting to disappearance the biggest animals and taming many others, digging rock and mud to grow magnificent cities where living structures once stood.
But the changes humans have made in recent decades have been on such a scale that they have altered our world beyond anything it has experienced in its 4.6 billion-year history. Our influence is no longer confined to a local area or even a region -- it's global, and so profound, it is pushing the planet into a new age that geologists are calling the Anthropocene, the Age of Humans.
Millions of years from now, a stripe in the accumulated layers of rock on Earth's surface will reveal our human fingerprint just as we can see evidence of dinosaurs in rocks of the Jurassic or the explosion of life that marks the Cambrian. Our influence will show up as changes in the chemistry of the oceans, the loss of forests and the growth of deserts, the damming of rivers and the retreat of glaciers. The fossil records will show the extinctions of various animals and the abundance of domesticates, the chemical fingerprint of artificial materials, such as aluminum drinks cans and plastic carrier bags and the footprint of projects like the Syncrude mine in the Athabasca oil sands of north-eastern Canada, which moves twice as much earth every year than flows down all the rivers in the world in that time.
In the Anthropocene, humanity has become a geophysical force on a par with the earth-shattering asteroids and planet-cloaking volcanoes that defined past eras. Earth is now a human planet. We decide whether a forest stands or is razed, whether pandas survive or go extinct, how and where a river flows, even the temperature of the atmosphere. We are now the most numerous big animal on Earth, and the next in line are the animals we have created through breeding to feed and serve us. Four-tenths of the planet's land surface is used to grow our food. Three-quarters of the world's fresh water is controlled by us. It is an extraordinary time. In the tropics, coral reefs are disappearing, ice is melting at the poles and the oceans are emptying of fish because of us. Entire islands are vanishing under rising seas, just as naked new land appears in the Arctic.
No part of this planet is untouched by human influence. We have transcended natural cycles and altered the physical, chemical and biological processes of the planet. Humans have the power to heat the planet further or to cool it right down, to eliminate species and to engineer entirely new ones. We have invented robots to be our slaves, computers to extend our brains and an ecosystem of networks with which to communicate. We have shifted our own evolutionary pathway with medical advances that save those who would naturally die in infancy. We have surmounted the limitations that restrict other species by creating artificial environments and external sources of energy. A 72-year-old man now has the same chance of dying as a 30-year-old caveman. We are supernatural: we can fly without wings and dive without gills; we can survive killer diseases and be resuscitated after death. We are the only species to leave the planet and visit our moon.
The realization that we wield such planetary power requires a quite extraordinary shift in perception, fundamentally toppling the scientific, cultural and religious philosophies that define our place in the world. Up until the Middle Ages, man was believed to be at the center of the universe. Then came Nicolaus Copernicus in the sixteenth century, who put Earth in its place as just another planet revolving around the sun. By the nineteenth century, Charles Darwin had reduced humans to just another species -- a twig on the grand tree of life. But now, the paradigm has shifted again: we are no longer just another species. Humans have become the masters of our planet and integral to the destiny of life on Earth.
And what about the impacts of our changed planet on us? After all, we've evolved and adapted to a life in the Holocene, and the new changes have occurred very rapidly. In changing the Earth, we have been able to live longer and healthier, in greater numbers than ever before. However, for now at least, humans are still of nature. We evolved on this living planet; we are made of cells. We breathe air, drink water and eat protein. We rely on the planet to provide everything -- all our materials, fuels, food and clothes; to clean our air, recycle our water and manage our waste. Our growing population and the way we live in this new human world are making us more demanding than ever of our planet's resources and processes, reducing its ability to meet our needs.
How will we deal with the consequences of the Anthropocene we have created? We have always altered ecosystems to serve our needs and presumably will continue to do so. We have improved the planet for our survival in a number of ways, including by staving off the next ice age, but we have also made it worse. Some of those negative consequences we can overcome through technological advances or migration or other adaptations. Others we will need to reverse; some others we will need to learn to live with.
And while science may be able to identify biophysical issues, it cannot tell us how to react -- that is for society to decide. Humans are no longer just another animal; we have specifically human rights that are expected to be achieved through development, including access to sanitation and electricity -- even the Internet. Delivering social justice and protecting the environment are closely linked; how poor people get richer will strongly shape the Anthropocene.
The enormous impacts we're having on our living planet in the Anthropocene are a direct consequence of the immense social changes we're undergoing -- changes to how we live as a species. We now support a massive global population, but we have not simply multiplied the number of small hunter-gatherer communities. More than half of the world's people now live in cities -- artificial constructs, which act as giant factories consuming the planet's plants, animals, water and mineral resources.
Humanity operates on an industrial scale and has needs -- currently, 18 terawatts of the energy at any time and 9 trillion cubic meters of fresh water per year. Humanity has become a super-organism. The intelligence, creativity and sociability of this super-organism is down to an accumulation of human brains, including those from the past who have left a cultural and intellectual legacy and also the artificial minds of our technological inventions, such as computer programs and information libraries like Wikipedia. Humanity is a global network of civilizations with a stream of knowledge already being channeled for human protection.
The self-awareness that comes with recognizing our planetary power also demands we question our new role. Are we just another part of nature, doing what nature does: reproducing to the limits of environmental capacity, after which we will suffer a population crash? Or are we the first species capable of self-determination, able to modulate our natural urges, our impacts and our environment, such that we can maintain habitability on this planet into the future? And what of our relationship to the rest of the biosphere? Should we treat it -- as every other species does -- as an exploitable resource to be plundered mercilessly, or does our new global power imbue us with a sense of responsibility over the rest of the natural world?
A few years ago, I left London and set off to explore the globe at the beginning of this new Anthropocene, meeting the pioneers who are negotiating a development path through the complexity of our shared biosphere. As humanity faces its biggest challenge in 10,000 years, I found remarkable people living in extraordinary times.
And I returned with hope that, in some respects the Anthropocene could be as good as, or better than, human history thus far. For that to happen, though, we need to think differently and globally, to accept ownership of the planet. The alternative is to jeopardize our future and that of many other species.
Adapting to the Anthropocene means understanding the social dimensions of our physical, chemical and biological changes to the planet's environment. That means understanding humans and our societal constructs including economics, cultural preferences and the way we interact with the natural world.
More profoundly, we need to reset our world views. Our institutions, governance systems, food production, water extraction, product design, manufacture and lifestyles are geared for a previous era -- a time of lower human population, stable climate and plentiful resources. The Anthropocene requires us to look at the world -- and engage with it -- from a new perspective. Only then will we design ways to produce food, water and energy and create livable conditions for the Earth's species.