Insurance companies, politicians, and businesspeople often use the expressions "natural disaster" or "act of God" to deflect responsibility for events beyond our control. Today, human activity and technology have become so powerful that we are contributing to what were once natural disasters.
Hurricanes, tornadoes, freak storms, floods, droughts, pest outbreaks, heat waves, and even earthquakes are occurring with greater frequency and intensity than ever. Some of this can be traced to human activity. Greenhouse gases, immense dams, and deep oil and water wells can all affect natural forces.
Since life first appeared on Earth some four billion years ago, it has played a critical role in altering the physical and chemical properties of the planet. For the first couple of billion years, it was a microbial world, yet those microscopic organisms acted with other forces to break down rock. Over time, this process reduced mountains and boulders to stones, gravel, and dust, releasing minerals and creating soils from the carcasses of organisms.
Life is thought to have evolved in oceans. Here, carbon from the atmosphere dissolved in the water to form carbonaceous shells that offered protection for some life forms. When these died, they sank to the ocean floor where eventually their accumulated shells were pressurized into limestone. Limestone is rock, created by life, which stores carbon in the ground.
As life forms evolved, they grew bigger, in part by incorporating and storing water. In doing so, they became a critical part of the hydrologic cycle, the process whereby water evaporates, forms clouds, and rains back on the Earth in an endless cycle. Organisms could take up dissolved minerals and trace chemicals from the water and release them with their own wastes. After plants evolved into trees on land, they became efficient at sucking water from soil and transpiring most of it into the air to affect weather and climate.
The evolution of photosynthesis was a huge biological breakthrough, enabling Earth's life to capture vast amounts of energy in the form of sunlight. During photosynthesis, plants release oxygen. Over millions of years, this process reduced the amount of carbon dioxide in the atmosphere while creating oxygen-rich air that animals like us depend on.
So for billions of years, the web of life has played a crucial role in changing the physical, chemical, and biological features of the planet. Life was not just opportunistic in exploiting physical and chemical opportunities; living organisms interacted with and changed the planet's earth, water, and air, or biosphere. But it took vast periods of time and millions of diverse species. In all that time, no single species was able to rapidly alter the properties of Earth on a geological scale — until now.
Humans appeared during the last moment of evolutionary time, perhaps 150,000 years ago. For most of our brief existence, we were tribal animals who didn't even know whether other humans lived on the other side of an ocean, desert, or mountain. We only had to worry about our own territory and tribe.
Suddenly, we have become a geological force, the most prolific mammal on the planet, endowed with powerful technologies, impelled by an insatiable appetite for stuff, and supplied by a global economy. Taken together, our numbers, technology, consumption, and global economy have made us a new kind of force on the planet. For the first time, we must ask, "What is the collective impact of 6.8 billion human beings?" As we begin to answer that question, we are left with the extreme difficulty of responding to global threats that our own activity has caused.
Many people harbour an understandable tendency to deny the reality of the crisis in the biosphere. After all, how can puny humans have such a massive impact on this large planet? Some also maintain a conceit that we can manage our way out of the mess, increasingly with heroic interventions of technology. But we've learned from past technologies — nuclear power, DDT, CFCs — that we don't know enough about how the world works to anticipate and minimize unexpected consequences.
The truth is that the only factor or species we can manage on Earth is us. We have no choice but to address the challenge of bringing our cities, energy needs, agriculture, fishing fleets, mines, and so on into balance with the factors that support all life. This crisis can become an opportunity if we seize it and get on with finding solutions.