Scientists and policymakers are meeting this week to discuss whether geoengineering to fight climate change can be safe in the future, but make no mistake about it: We're already geoengineering Earth on a massive scale. From diverting a third of Earth's available fresh water to planting and grazing two-fifths of its land surface, humankind has fiddled with the knobs of the Holocene, that 10,000-year period of climate stability that birthed civilization.
The consequences of our interventions into Earth's geophysical processes are yet to be determined, but scientists say they're so fundamental that the Holocene no longer exists. We now live in the Anthropocene, a geological age of mankind's making.
"Homo sapiens has emerged as a force of nature rivaling climatic and geologic forces," wrote Earth scientists Erle Ellis and Navin Ramankutty in a 2008 Frontiers in Ecology paper, which featured their redrawn map of the human-influenced world. "Human forces may now outweigh these across most of Earth's land surface today."
Geologic epochs are distinguished from one another based on geological observations, such as the composition of sediment layers and other tools of paleoclimatology. To justify the identification of a new Anthropocene epoch, it must therefore be demonstrated that evidence of anthropogenic global change is present at such a level that it can be distinguished using geologic indicators despite natural variability in these across the Holocene.
The most commonly cited and readily measured global change associated with humans is the rise of greenhouse gases, especially carbon dioxide and methane, around the beginning of the Industrial Revolution, together with the associated rise in global temperatures and sea level caused by this global warming. Other key indicators include massive global increases in soil erosion caused by land clearing and soil tillage for agriculture and massive extinctions of species caused by hunting and the widespread destruction of natural habitats.