8.4 THE ANTHROPOCENE
Since the advent of agriculture, Homo sapiens have altered the face of the Earth in a dramatic and accelerating fashion. fte impact of human activities has been so great, that some scientists have asserted that we are now in a new geological epoch, the Anthropocene, although this has not yet been formally adopted by the geological community. fte concept of an Anthropocene Epoch was popularized by atmospheric chemist Paul Crutzen and biologist Eugene Stoermer, and many scientists are using the term.
Debate has ensued regarding the official beginning of this epoch. Crutzen and Stoermer suggested the late 18th century, when James Watt’s improvement of the steam engine was an important factor in the beginnings of the Industrial Revolution. Others have suggested the birth of agriculture as an appropriate beginning of the epoch. In order to define a geological time unit, geological stratigraphic material must contain a record of global-scale synchronous change. Several potential start dates/events have been proposed, ranging from the megafaunal extinctions that began roughly 50,000 years ago, to the origins of agriculture, to the presence of persistent industrial chemicals beginning about 1950.
In a recent paper in the prestigious journal Nature, Lewis and Maslin suggest that the above proposed start dates generally do not exhibit markers of sufficient global synchrony to be useful. ftey have proposed two potential start dates for the Anthropocene that do appear to meet this criterion – 1610 and 1964. fte year 1610 marks a dramatic decrease in the amount
of CO2 in the atmosphere, and this appears to correspond to the precipitous (~ 90%) decline in the indigenous human population of the New World after the arrival of Europeans. ftis
decline in the population of the New World, caused by disease, famine, and war, resulted in a significant decline in farming and the use of fire, which allowed regeneration of over 50 million ha of native vegetation. ftis increased vegetation in turn resulted in increased carbon uptake
and the decline in global atmospheric CO2. ftis date also corresponds to the beginnings of significant transoceanic movement of species. fte 1964 date corresponds to peak levels of
14C associated with radioactive fallout from nuclear bomb tests. With respect to early human evolution, an important question is “how did the geography of the Earth affect humans?” Now, an equally legitimate question is “how are humans affecting the Earth?” Regardless of the start date chosen for the beginning of the Anthropocene, there can be no doubt that H. sapiens is now the most important biological agent of change on Earth, and collectively we are changing the landscape, climate, and biodiversity of our planet in profound ways.
fte sum total of human impacts on the Earth is a function of human population size and the degree of impact per individual. During the last 10,000 years, the human population has increased from a few million individuals to over 7 billion as of the year 2011. Population growth is expected to continue for decades, although at a decreasing rate, and is expected to reach 10 billion in the late 21st century. ftus, the human population has increased over 1,000-fold in the last 10,000 years. However, this tremendous growth has not been uniform over time. For most of this time period, growth was relatively slow, and there were even periods of population decline, such as the substantial dip in the 14th century due to the “black death.” But in the last few centuries, the population has grown virtually exponentially; in the 20th century alone, the world human population increased by over 5 billion. ftis population growth has resulted in a corresponding increase in human impacts on the Earth.
However, population size is not the complete story. Individuals vary greatly in their capacity to change the Earth. One commonly used measure that depicts individual impacts on the Earth is the ecological footprint. ftis metric represents the area of productive land and sea that is required to supply the resources and absorb the wastes of a human population. Currently, the world human population has an ecological footprint that would require 1.5 Earths to supply the resources and assimilate the wastes of the current human population indefinitely. It is estimated that a sustainable level of ecological footprint would be 2.1 ha per person at our current population size, but that overall, the human population currently exceeds this by a wide margin. Obviously, this level of consumption and waste production is not sustainable. But examining this ecological footprint in more detail, we see that its size varies tremendously from country to country. fte United States and certain European, Asian, and Middle Eastern countries have ecological footprints of 6 ha per person or higher, whereas countries such as India, Haiti, and many African countries have ecological footprints below 1 ha per person (Fig. 8.8).