The Anthropocene and All That

From Yale Environment 360, "Living in the Anthropocene":

It’s a pity we’re still officially living in an age called the Holocene. The Anthropocene — human dominance of biological, chemical and geological processes on Earth — is already an undeniable reality. Evidence is mounting that the name change suggested by one of us more than ten years ago is overdue. It may still take some time for the scientific body in charge of naming big stretches of time in Earth’s history, the International Commission on Stratigraphy, to make up its mind about this name change. But that shouldn’t stop us from seeing and learning what it means to live in this new Anthropocene epoch, on a planet that is being anthroposized at high speed.
For millennia, humans have behaved as rebels against a superpower we call “Nature.” In the 20th century, however, new technologies, fossil fuels, and a fast-growing population resulted in a “Great Acceleration” of our own powers. Albeit clumsily, we are taking control of Nature’s realm, from climate to DNA. We humans are becoming the dominant force for change on Earth. A long-held religious and philosophical idea — humans as the masters of planet Earth — has turned into a stark reality. What we do now already affects the planet of the year 3000 or even 50,000.
Changing the climate for millennia to come is just one aspect. By cutting down rainforests, moving mountains to access coal deposits and acidifying coral reefs, we fundamentally change the biology and the geology of the planet. While driving uncountable numbers of species to extinction, we create new life forms through gene technology, and, soon, through synthetic biology.

This essay from the Economist (May 26, 2011) has more on the concept:

According to studies by Erle Ellis, an ecologist at the University of Maryland, Baltimore County, the vast majority of ecosystems on the planet now reflect the presence of people. There are, for instance, more trees on farms than in wild forests. And these anthropogenic biomes are spread about the planet in a way that the ecological arrangements of the prehuman world were not. The fossil record of the Anthropocene will thus show a planetary ecosystem homogenised through domestication. 

More sinisterly, there are the fossils that will not be found. Although it is not yet inevitable, scientists warn that if current trends of habitat loss continue, exacerbated by the effects of climate change, there could be an imminent and dramatic number of extinctions before long. 

All these things would show future geologists that humans had been present. But though they might be diagnostic of the time in which humans lived, they would not necessarily show that those humans shaped their time in the way that people pushing the idea of the Anthropocene want to argue. The strong claim of those announcing the recent dawning of the age of man is that humans are not just spreading over the planet, but are changing the way it works.  

Such workings are the province of Earth-system science, which sees the planet not just as a set of places, or as the subject of a history, but also as a system of forces, flows and feedbacks that act upon each other. This system can behave in distinctive and counterintuitive ways, including sometimes flipping suddenly from one state to another. To an Earth-system scientist the difference between the Quaternary period (which includes the Holocene) and the Neogene, which came before it, is not just what was living where, or what the sea level was; it is that in the Neogene the climate stayed stable whereas in the Quaternary it swung in and out of a series of ice ages. The Earth worked differently in the two periods. 

The clearest evidence for the system working differently in the Anthropocene comes from the recycling systems on which life depends for various crucial elements. In the past couple of centuries people have released quantities of fossil carbon that the planet took hundreds of millions of years to store away. This has given them a commanding role in the planet’s carbon cycle.  

Although the natural fluxes of carbon dioxide into and out of the atmosphere are still more than ten times larger than the amount that humans put in every year by burning fossil fuels, the human addition matters disproportionately because it unbalances those natural flows. . . . .The result of putting more carbon into the atmosphere than can be taken out of it is a warmer climate, a melting Arctic, higher sea levels, improvements in the photosynthetic efficiency of many plants, an intensification of the hydrologic cycle of evaporation and precipitation, and new ocean chemistry. 

All of these have knock-on effects both on people and on the processes of the planet. More rain means more weathering of mountains. More efficient photosynthesis means less evaporation from croplands. And the changes in ocean chemistry are the sort of thing that can be expected to have a direct effect on the geological record if carbon levels rise far enough.