“Not so long ago, the very nature of planet Earth suffered a devastating rupture,” writes ” writes Robinson Meyer in The Atlantic, about our emerging Anthropocene epoch. “The break was sudden, global, and irreversible. It happened in the year 1950. Mick Jagger, Meryl Streep, and Caitlyn Jenner were all born before this crack in time. Vladimir Putin, Liam Neeson, and Mr. T were all born after it.”
Earth’s uber-catastrophes are comfortingly rare, having struck only five times in the more than half a billion years since complex life emerged. But it’s a history, writes Peter Brannen in The Ends of the World, “that has frightening echoes in our own world—which is undergoing changes not seen for tens of millions, or even hundreds of millions, of years. “
It’s pretty clear that times of high carbon dioxide—and especially times when carbon dioxide levels rapidly rose—”coincided with the mass extinctions,” writes University of Washington paleontologist and End-Permian mass extinction.
What we’ve been up to should fill us with awe, observes Bill McKibbon in “Life On a Shrinking Planet” in the New Yorker. There have been at least four other episodes in Earth’s half-billion-year history of animal life when CO2 has poured into the atmosphere in greater volumes, but perhaps never at greater speeds. Even at the end of the Permian Age, continues McKibbon, when huge injections of CO2 from volcanoes burning through coal deposits in Siberia culminated in “The Great Dying,” the CO2 content grew at a tenth of the current pace.
But by the end of the Permian nearly everything would be dead: Siberia would turn inside out, spewing fiery lava over millions of square miles and swamping the atmosphere with volcanic gases. One gas in particular, writes Brannen, “stands out as the primary killer in what would become the greatest mass death in earth history. Researchers don’t study the worst catastrophe ever purely out of academic, or even morbid, curiosity. The End-Permian mass extinction is the absolute end-member—the worst-case scenario—for what happens when you jam too much carbon dioxide into the atmosphere.”
Two centuries ago, the concentration of CO2 in the atmosphere was 275 parts per million, It has now topped 400 parts per million and is rising more than two parts per million each year. The extra heat that we trap near the planet every day is equivalent to the heat from 400,000 bombs the size of the one we dropped on Hiroshima.
Until now, human beings have been spreading from our beginnings in Africa, out across the globe, slowly at first writes McKibbon, and then much faster. But a period of contraction is setting in as we lose ever larger parts of our habitable planet, with wildfires, heat waves, and rising sea levels. Sometimes our retreat will be terrifying and violent as when blazing California towns along narrow roads was so chaotic that many people were incinerated in the cars.
Later this month, April 2019, a committee of researchers from around the world will vote on two questions. First, should the Anthropocene be added as a new epoch to the Geological Time Scale, the standard scientific timeline of Earth’s 4.5-billion-year history? Second, should the Anthropocene, if it does exist, begin in the middle of the 20th century?
If accepted, this delineation will signal a new reality, that human activities, writes Meyer, not natural processes, are now the dominant driver of change on Earth’s surface—”that carbon pollution, climate change, deforestation, factory farms, mass die-offs, and enormous road networks have made a greater imprint on the planet than any other force in the past 12,000 years.”
William Ruddiman, a professor of environmental sciences at the University of Virginia, is extremely worried about climate change, but he nonetheless hopes the committee votes against both questions. For the past two years, he has lobbied its members to think of the Anthropocene not as a sudden upheaval, but as a gradual change, a slow transformation of the planet that began 5,000 years ago. “Where could you possibly pick a single start date in this ever-evolving story?” he asked Meyer in an email.
Trained as a marine geologist, Ruddiman for the past fifteen years has worked on a hypothesis that posits that pre-industrial age humans raised greenhouse gas levels in the atmosphere. Looking back seven thousand years into the Holocene—the current 11,500-year-old geological epoch—Ruddiman has proposed that early agriculture emitted enough methane and carbon dioxide to offset what would have been a global cold cycle. Ruddiman says that in contrast to the familiar view that human-caused greenhouse gases began with the industrial revolution, “the baseline of human effects on climate started earlier and that the total effect is larger.”
Last week, he and 23 other researchers argued the topic at length in the scientific journal Progress in Physical Geography. At stake is a seemingly simple question: When did human influence over the environment reach a tipping point?
For Jan Zalasiewicz, a professor of geography at the University of Leicester, the answer is clear. Zalasiewicz chairs the Anthropocene Working Group, the committee that will soon vote on the existence of the epoch.
“If you look at the main parameters of the Earth-system metabolism, then … things only began to change sharply and dramatically with industrialization,” Jan Zalasiewicz, a professor of geography at the University of Leicester, told Meyer. Zalasiewicz chairs the Anthropocene Working Group, the committee that will soon vote on the existence of the epoch. He believes that the most significant event in humanity’s life on the planet, continues Meyer, “is the Great Acceleration, the period of rapid global industrialization that followed the Second World War. As factories and cars spread across the planet, as the United States and U.S.S.R. prepared for the Cold War, carbon pollution soared. So too did methane pollution, the number of extinctions and invasive species, the degree of surface-level radiation, the quantity of plastic in the ocean, and the amount of rock and soil moved around the planet.”
It was “the Big Zoom,” Zalasiewicz said. There is “nothing really comparable” to that shift in any other period of Earth history. Even setting carbon pollution aside, he said, the spike in fertilizer use led to the largest jump in surface nitrogen levels in 2.5 billion years. Zalasiewicz hopes the committee will start the Anthropocene in the middle of the 20th century. Zalasiewicz and 16 of his colleagues wrote that any human-induced changes prior to 1950 paled in comparison with those that came after.
Ruddiman isn’t so sure. He believes that humanity’s effect on the planet is spread throughout time and is driven primarily by agriculture. Before the year 1750, he argues, humans had already cleared so much forest as to produce 300 billion tons of carbon emissions. Since 1950, deforestation has only led to 75 billion tons of emissions.
Humans remade the planet in other ways, too. About 12,000 years ago, we drove a huge swath of American mammals, including the giant ground sloth, into extinction. About 11,000 years ago, we entered into unprecedented relationships with crops and some livestock, domesticating them and taming their genome. Between 6,000 and 7,000 years ago, humans began clear-cutting forests to create new agricultural land; they may have transformed much of Europe by doing so. And by about 1,000 years ago, as humans embraced tilling and made rice paddies, they began moving more dirt and rock around the surface of the planet than is moved naturally.
“I don’t think it’s possible to put an exact date” on the Anthropocene, Ruddiman told Meyer last week. “It goes on continuously for 12,000 years. There’s no obvious break point. Even just the invention of tilling—it’s huge.” For that reason, he believes that the committee shouldn’t add a capital-A Anthropocene to the geological timeline. Instead, scientists should talk about the “lower-a anthropocene”—a set of profound changes wrought to Earth over the course of millennia, across many different places. They culminate in the biggest anthropocene of all: modern, human-caused climate change.
It is important to say modern, for Ruddiman believes that humans have already shifted the climate once before. About a decade ago, he proposed what’s called the “early anthropocene hypothesis”—a theory that ancient agricultural clear-cutting added so much carbon to the atmosphere that it effectively stopped Arctic glaciers from expanding more than 3,000 years ago. If not for that deforestation, then there would be an additional Greenland’s worth of ice in the Canadian Arctic today, he said.
Of the working group’s 37 members, 17 members signed their name to Zalasiewicz’s paper, and only five signed their name to the more skeptical review. That leaves 15 committee members unaligned in advance of the upcoming vote. “You’d think people who served on a committee for years would be more willing to put their name on paper,” Ruddiman said. The vote will take place electronically and continue through May. If it succeeds, then the committee will busy itself with the next task: finding evidence in the rock record of the precise moment that humanity pushed Earth into a bewildering new era.