Over the course of earth’s history, there have been five cataclysmic events that have radically altered—or ended—life for the planet’s inhabitants. Author and journalist Elizabeth Kolbert argues that humanity’s growing influence over climate and ecosystems is ushering in a sixth catastrophe that large swaths of plants and animals—including humans—may not survive.

About 200,000 years ago, a species emerged on the scene that would come to alter its environment in profound—and sometimes cataclysmic—ways. The species is not especially strong or fast, but it is extremely creative and can make the most of just about any environment in which it lives. It’s a terrestrial mammal, but it managed to cross oceans and settle in just about every corner of the world. The advent of Homo sapiens led to the decimation of numerous local species in the regions to which it migrated, like Australia and, later, the Americas.

About 12,000 years ago, Homo sapiens became less migratory and began to establish more permanent settlements. Its population boomed, and they leveled large sections of forest for housing and farmland. Even more significantly, the ever-inventive species developed ways to harvest natural resources below the earth’s surface. Burning these fuels led to alterations of the atmosphere, climate, and oceans.

Welcome to the Anthropocene. This neologism coined in the early 2000s describes the geological period in which Homo sapiens began to shape and radically alter the environment. There have been five cataclysmic moments when earth’s biodiversity has been almost utterly destroyed. Some refer to them as the Big Five. The timing is remarkable and even tragically comic: humans are uncovering more about the Big Five as they discover that they are currently creating the conditions for a sixth—the Sixth Extinction.

Ocean acidification is a disconcerting development that scientists have identified. Just two decades ago, little work had yet been done on the effect of CO2 emissions on ocean pH levels.  Ken Caldeira of Stanford University was brought on by the Department of Energy to investigate the ramifications of injecting smoke stack emissions into the deep ocean. Caldeira also researched what the effect current practices (releasing CO2 into the atmosphere) had on the oceans when their surface waters absorbed the compound. In 2003, he published a paper arguing that over the next few centuries, we might see more acidification than the world has experienced over the past third of a billion years. Its ramifications for wildlife continue to be discovered. Perhaps most notably—and tragically—are the world’s coral reefs.

Reefs form a band around the center of the earth, thriving between 30 degrees north and 30 degrees south. Some have pointed out their similarities to rainforests in how they function. The amazing biodiversity is one obvious point of comparison. Coral has been dissected in different labs to measure biodiversity, and it is often surprising how many species are contained in a chunk of coral. In one square foot of coral studied, over 100 species of worm were discovered. What makes the biodiversity even more surprising is that the tropical waters in which reefs thrive tend to be nutrient-poor. More than tropical forests, reefs are tropical forests that grow up in a desert.

Ocean acidification is not the only threat that the wide waters face. Arguably even more pressing concerns are overfishing, deforestation (which diminishes water clarity), and dynamite fishing (yes, this is real: people literally blow schools of fish out of the water, stunning or killing them to make collection easier).

Another hazard—and a natural corollary of ocean acidification, is climate change, which is causing the oceans’ temperatures to rise. When the temperature rises above a certain point, the symbiotic relationships that enable coral to grow and thrive break down. The reefs stop growing and turn blanch white. They go from wildly colorful and full of life to bone white and lifeless. Scientists project that over a third of coral species will soon be extinct if acidification and temperature continue to rise.

When most people think of global warming, they tend to view cold-loving species as the most vulnerable. (Think polar bears on shrinking ice caps.) This might be the case, but rising temperatures also pose a threat to organisms that thrive in the warmer climes. In the tropics, for instance, where most terrestrial organisms live, plants and animals are entering dire straits.

As a general rule, biodiversity increases the farther you move from the poles and closer to the equator. So New York has far more diversity than northern Canada, and Brazil has far more than New York. This is known as the latitudinal diversity gradient, or LDG. There are some 30 hypotheses about the trend—everything from the tropics having expedited evolutionary processes, to containing more fragile organisms, to being longer-established ecosystems.

Whatever the explanation may be, the fact remains that tropical regions are teeming with an astonishing amount of diversity far exceeding the temperate and taiga climes closer to the poles.

As CO2 levels and temperatures are rising to degrees not seen for millions for years, the animals in the tropics might have to migrate to different regions and establish new niches. If species are as mobile as some of the more optimistic models predict, it is still likely that more than 10 percent of species will be extinct by 2050. By the no-dispersion metrics, which predict that organism migration will be minimal or non-existent, those rates of extinction will be much higher—between a quarter and half of all species. The variation will depend on how quickly global temperatures rise over the next several decades.

The situation is even direr for trees and other plant life. Plants cannot migrate, so the question becomes whether they can reacquire adaptations that were left behind millions of years ago. They would need to do so with an unprecedented swiftness in order to survive.

A pandemic recently broke out among various species of bats in the northeastern United States. It began in upstate New York, when scientists making a routine visit to a nearby cave found bats dead on the floor instead of hanging from the ceiling for the winter, each covered in a white powdery substance. Zoologists were confused by the phenomenon. Some joked that the bats had scored some cocaine, but the tone became more sober when the powder began spreading across the northeast.

The following year, it’d spread to 33 caves across four states. In some caves typically frequented by bats, the population plummeted by 90 percent. The year after that, the fungus was affecting bats in five other states.

The powder turned out to be a white fungus called psychrophile. It’s probably native to Europe, and it has continued to decimate the bat population in the United States. Three species of bat are now on the endangered list.

This is just one of numerous cases of non-native species driving native species to the point of extinction. As mentioned earlier, humans did this very thing as they migrated. With humans, animals, plants, and pathogens, the introduction of a new species blindsides local ecosystems that are used to competing and adapting to specific patterns developed slowly over time.

One of the hallmarks of the Anthropocene is the creation of highways and byways across land and sea. World travel and international trade have facilitated an unprecedented level of invasion because nothing is remote anymore. A single large merchant vessel or a commercial plane can easily undo millions of years of adaptation and eco-equilibrium because of the foreign species that people knowingly or unwittingly bring with them.

At this point in history, you could probably spot an invasive species just by looking out your window—even if you don’t know it as such. Some scientists have called this phenomenon “New Pangaea,” referencing the period in earth’s history when there was one large land mass. After the continental drift, niches and ecosystems emerged particular to the isolated continents. This was especially pronounced in island ecosystems. With thousands of invasive species being introduced through our systems of highways and byways, the world is being “brought together.” Local biodiversity indices might rise—at least until the invader dies or manages to reproduce and threaten local ecosystems—but global biodiversity will continue to drop as long as New Pangaea continues.

One exhibit in the American Museum of Natural History references the Sixth Extinction. The accompanying plaque reads that, “Global climate change and other causes, probably including collisions between earth and extraterrestrial objects" led to five mass extinctions. "Right now we are in the midst of the Sixth Extinction, this time caused solely by humanity’s transformation of the ecological landscape.” Beneath the plexiglass display are the fossilized remains of victims from the past five catastrophes. The exhibit appears intentionally unfinished, leaving space for the fossils that would fill the Sixth Extinction. Will Homo sapiens fossils someday become features of the Sixth Extinction?

Will we be undone by the very changes we have wrought on the planet? This is one possibility that the museum exhibit strongly suggests: humans have the capacity to disrupt vital biological and geological processes—sea levels, ocean chemistry, constitution of the atmosphere, the biodiversity of vital ecosystems—and we will reap what we’ve sown. This book places a great deal of emphasis on ecosystems and the decimation of biodiversity. The skeptic may question what the extinction of other species has to do with our own. The truth is that it has everything to do with our survival. One ecologist has compared humans driving other species out of existence to hacking at the branch on which they are precariously sitting. The analogy is an apt one.

Another possibility is that this creative—if troublesome—species will innovate its way out of this position, and ultimately evade catastrophe. There are suggestions for reversing global warming or even preparing for a mass exodus to nearby moons and planets.

At the risk of sounding anti-human, our problem is much broader in scope than the human race. In either of the above scenarios, we must choose our next moves carefully.

Just outside San Diego, at the Institute for Conservation Research, there’s a lab that’s popularly known (and trademarked) as the Frozen Zoo. In a secretive, windowless room, contained within airtight vaults that are set at a temperature of -328 degrees Fahrenheit, are vials containing genetic material from about 800 different species. In anticipation of endangered species disappearing as a result of global warming, ocean acidification, deforestation, invasive species, overfishing, and poaching, the Institute is trying to preserve a legacy.

The primary goal of this book is to show that Homo sapiens is capable of instigating a global drama that could become a tragedy. It’s less a rallying cry suggesting that if people cared more about the environment, we could reverse the trends of the Anthropocene. The same qualities that make humans unique—our restless hunger to explore and to know, our inventiveness, our ability to convey complex meaning and work effectively in large numbers—are the same that have led to tremendous influence on our world.

People have the capacity for destruction and missing the big picture. But there is also a proud tradition of those people who have worked to protect our planet from destruction. While it’s not clear whether or not we can reverse it, it makes best sense to focus on the small, but concerted efforts that people are making, instead of brooding over an impending cataclysm. We must continue to have hope.