A human-dominated planet: is there any nature left?

The scientific argument for the end of nature, as put forward by McKibben, goes something like this: With the onset of the industrial revolution (roughly around 1800), humans, primarily through the burning of fossil fuels, began to release significant amounts of “greenhouse gases” (mainly carbon dioxide, but also methane, nitrous oxide, and fluorinated gases) into the atmosphere, thereby altering the carbon cycle and changing the chemical composition of the atmosphere. These atmospheric changes, in turn, amplified the natural “greenhouse effect,” i.e. the trapping in the atmosphere of solar radiation reflected from the Earth’s surface, which would otherwise escape back into space. To be clear, the greenhouse effect is necessary to maintain surface temperatures that can sustain life on Earth. However, an excess concentration of greenhouse gases in the atmosphere leads to net warming of the planet, with temperatures deviating from ranges of natural (or historical) variation, thus threatening to disrupt the conditions under which organisms and societies on Earth have evolved. Net warming of the planet affects nearly every aspect of natural and human systems, with far-reaching, grave consequences for the entire community of life. 

In affecting the climate and weather everywhere, human industrial activity now has a ripple effect on Earth’s complex web of life. Warmer temperatures, reduced precipitation, declining snowpack, extended droughts, increased wildfire, rising sea levels, increased frequency in extreme weather events (e.g., floods, storms, heatwaves), melting glaciers and sea ice, and biodiversity loss are just some of the consequences attributed to a changing climate. Hence, in disrupting the carbon cycle, humans are not only changing the chemical composition of the atmosphere, but they are also, at least indirectly, altering Earth’s biosphere, hydrosphere, and lithosphere. In the face of the overwhelming scientific evidence supporting that the unfolding climate crisis is human-caused, McKibben observes that “for the first time human beings had become so large that they altered everything around us.” He further laments that “our appetites and habits and desires could now be read in every cubic meter of air, in every increment on the thermometer.” 

It is true that humans, like all species, have always modified their surroundings in some form. However, in significantly changing the climate, humans are now altering even those places where they are not. Every inch of the planet is now different because of us. Humans have cast a veil over this planet that will affect all life on Earth for the foreseeable future and that will permanently alter the trajectory of evolution. As a result, McKibben concludes that we now live in a “post-natural world,” where human influence is ubiquitous and where everything is artificial to some degree. Anthropogenic forces have become so intertwined and entangled with natural systems that we have effectively ended nature as an independent force.

In recognition of the dramatic environmental changes taking place due to the rapidly growing scale of the human enterprise, some scientists have proposed demarcating an entirely new geologic epoch called the “Anthropocene.” While the term has yet to be accepted formally as a new epoch (or era) in the geologic time scale, the term has been widely adapted in the global research community. At its core, the concept of the Anthropocene rests on the mounting scientific evidence that humanity itself has become a global geophysical force that is radically altering conditions on Earth to the extent that is thought to leave a significant, permanent mark in the geologic record. Homo sapiens won’t be just another species that came and went, another array of fossils whose story is remembered in future rock strata. Homo sapiens has likely already changed the very trajectory of those strata and thus forever altered the course of Earth’s four-billion-year-old history. As Steffen in his article ‘The Anthropocene: Are Humans Now Overwhelming the Great Forces of Nature?’ put it, “human activities have become so pervasive and profound that they rival the great forces of Nature and are pushing the Earth into planetary terra incognita.”

Climate change is generally considered the most prominent sign of human-driven changes to the global environment. However, as researchers point out, “climate change is only the tip of the iceberg.” In addition to altering the carbon cycle, humans are significantly impacting numerous other Earth system processes. The rapidly expanding human influence and pressure on the Earth system is perhaps best illustrated through the lens of the planetary boundaries framework. This framework proposes nine critical biophysical processes that regulate the stability of the Earth system, including climate change, ocean acidification, stratospheric ozone depletion, biogeochemical flows (nitrogen and phosphorus), freshwater use, land-system change, changes in biosphere integrity (genetic diversity, functional diversity, rate of biodiversity loss), atmospheric aerosol loading, and chemical pollution. For each of these processes, scientists have identified planetary boundaries (i.e., thresholds or tipping points), the transgression of which threatens to destabilize the Holocene state of the Earth System in which modern societies have evolved. Collectively, these planetary boundaries “define a safe operating space for humanity”. Or, as others put it, the planetary boundaries constitute “non-negotiable planetary preconditions that humanity needs to respect in order to avoid the risk of deleterious or even catastrophic environmental change at continental to global scales.”

Already, scientists estimate that humans have transgressed four of the nine planetary boundaries. As of January 2021, atmospheric carbon dioxide concentration has been measured at 415 parts per million (ppm), far exceeding the planetary boundary of 350 ppm. The integrity of the biosphere is also under threat, with current extinction rates estimated to be 300, 400, or even 2,700 times higher than the background extinction rate. Researchers predict that the extinction rate will rise considerably in the future in the absence of large-scale conservation efforts. A United Nations report found that one million animal and plant species are already threatened with extinction. Averting such a dramatic loss in biodiversity, also referred to as the sixth mass extinction, will require a monumental effort, a global response on part of our species to protect and restore nature.

In addition, humans, mainly through mining and use of fertilizer, have significantly altered the global phosphorus and nitrogen cycles, disrupting the ratios of these elements between the land and waters, with detrimental consequences for many ecosystems and organisms. Humans have also dramatically changed the pattern and composition of terrestrial biomes, leading to the disappearance of forests, savannas, grasslands, tundra, and so on. For example, a century ago, only 15% of Earth’s surface was used to grow crops and raise livestock. Today, more than 77% of land has been directly modified by the effects of human activities. Worrisomely, these trends are continuing and even accelerating. Between 1993 and 2009 alone, an area of terrestrial wilderness larger than India was lost to human settlement, farming, mining, and other pressures.

Finally, humans are pushing the limits of additional planetary boundaries. Thus far, the oceans have absorbed a significant portion of the carbon released into the atmosphere by humans. As a result, the chemistry of the ocean surface waters is acidifying, and experts warn that the oceans may soon change from a carbon sink to a source of atmospheric carbon (this also highlights the interactions and feedbacks between planetary boundaries). Similarly, global consumptive use of freshwater is increasing, threatening the functioning of flow-dependent ecosystems, such as rivers and streams, which play a disproportionate role in sustaining biodiversity on Earth. Lastly, humans are introducing novel, synthetic entities (e.g., microplastics, pesticides) into the environment at an alarming rate, with yet largely unknown risks to the functioning of the Earth system.

As we look ahead, the human population and the power of technology are only projected to grow. When contemplating future anthropogenic climate change, population growth, and the possibilities of geoengineering, artificial intelligence, and synthetic biology, McKibben predicts, “we will live, eventually, in a shopping mall, where every feature is designed for our delectation.”

In summary, there is mounting scientific evidence that we have entered the Anthropocene. Our massive tampering with the atmosphere, biosphere, lithosphere, and hydrosphere has put Homo sapiens in an unprecedented spot in the history of life on Earth. We live in an age where humans are carrying out a geophysical experiment of planetary proportions with largely unforeseeable consequences. However, one thing we do know: the human enterprise is on a collision course with the rest of the living world (and thereby eroding its own life-support system). Nature no longer exists as a separate, independent force on our planet. In the Anthropocene, natural and human forces have become fiercely and deeply intertwined. As ecologist Peter Vitousek puts it, “we live on a human-dominated planet,” where “many ecosystems are dominated directly by humanity, and no ecosystem on Earth’s surface is free of pervasive human influence.”