new history

Human activity may have altered the Earth much earlier than we thought

The history of human influence on the Earth is being rewritten.

Aerial shot of a large oil refinery in East Toledo, Ohio on a summer morning.
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The Industrial Revolution went into high gear in the late 18th century. To feed the fires of industry, humans began to extract ever more resources from planet Earth and tear down ever more forests to make room for our burgeoning species’ numbers.

Thus began humanity’s devastating campaign to irrevocably alter the face of the planet — and kickstart a new geological age now known as the Anthropocene. Or at least, that’s the story scientists have been telling us — but that history may be a lie. The truth, in fact, maybe much more insidious.

What’s new — Humans may have been indelibly altering the environment for thousands of years prior to the Industrial Revolution. That’s according to a new study published in the journal Science that holds some ominous implications for the future of planet Earth.

The study analyzes changing vegetation patterns over the last 18,000 years using fossilized pollen records to gauge how our environment has changed and morphed over time. The researchers found unprecedented global vegetation change — particularly to forests — occurred between 2,900 and 4,600 years ago, during what is known as the late Holocene period.

The scientists aren’t 100 percent sure what caused the rapid shift in vegetation change, Suzette Flantua, a co-author on the study and researcher in the department of biological sciences at the University of Bergen, tells Inverse. But they think humans are — at least in part — to blame.

“We do suspect that human activity played a significant role,” she says.

The findings show how far back human influence over Earth extends, even to a period of time when there was only modest climate change.

The results are striking: Vegetation change during the late Holocene was even more rapid than during the deglaciation period after the last Ice Age (8,000 to 20,000 years ago). This time in Earth’s history is one of the most significant periods of climate change prior to today.

Jonathan Overpeck is a professor of environmental education at the University of Michigan and the author of a related article on the study. Overpeck tells Inverse the findings are surprising.

“The rate of global vegetation change was higher over the last several thousand years, when the rate of global climate change was modest, than it was during the last deglaciation when the rate of climate change was much larger,” he says.

Fossil pollen is an excellent way to understand change in vegetation over time, the researchers say. This graphic explains how they extract and analyze fossil pollen from lakes.

Artwork by Milan Teunissen van Manen

How they did it — To come to this paradigm shift, the scientists turned to a seemingly strange source of information: fossil pollen. Yes, the very same plant sperm that makes you sneeze uncontrollably in pleasant spring weather may be the key to explaining the effect of human activity on the planet.

“[Pollen] become distributed through wind dispersal and pollinators and accumulate naturally in lakes and bogs and so,” Flantua says. “They can accumulate there for thousands of years and are therefore then called ‘fossil pollen.’”

The scientists then use a tube-shaped device to “core,” or remove sediment, from these lakes, analyzing the muck for fossil pollen. The researchers ultimately collected more than 1,000 samples from every continent except Antarctica.

Fossil pollen essentially acts as a natural record-keeper for planet Earth, according to the researchers, making it a great resource to study changes in the planet’s history.

“As vegetation changes through time, the fossil pollen composition detected in the cores changes accordingly and that’s how they can be used to track changes in vegetation,” Flantua says.

A map showing where the scientists extracted fossil pollen from around the world, using the pollen to calculate changes in vegetation over the past 18,000 years.

Photo credits: John W. Williams (a,b,r); Steffen Wolters (c,d,f,g); Thomas Giesecke (e); Henry H. Hooghiemstra (h,l,n,o,q); Geoff Hope (i); Feli Hopf (j); Eric Colhoun (k), Sarah Ivory (m), Luciane Fontana (p). Figure credit: Suzette Flantua.

Why it happened — Scientists understand what happened to the vegetation, but why is less clear. Correlation is not causation, after all, and even though the rise of complex human civilizations thousands of years ago may have spurred a change in vegetation, we can’t be certain.

“That is difficult to say because we detect patterns of vegetation change but we do not address why these changes occurred for different continents and sub-regions,” Flantua says.

The researchers launched the Human on Planet Earth (HOPE) project, which seeks to provide a “direct link between the human impact on the ecosystem during the Holocene period,” according to Flantua.

Why it matters — But even without knowing for certain that humans caused the vegetation change, the study’s findings still should worry you, researchers say. They have grave implications for our future survival on planet Earth, including our ability to withstand the climate crisis.

According to Overpeck, the study “implies that the threat of future vegetation change is even larger than we thought due to the one-two punch of direct human alteration of vegetation plus the growing impacts of human-driven climate change.”

Flantua adds, “If humans indeed drove the recent acceleration, then it would be mean the human legacy has a proven moment in time in the vegetation and this has implications for what policymakers would consider as “pristine” landscapes.”

The study’s findings mean that we should act with greater urgency to halt the current climate crisis, researchers say, including better forest management. Changes in forest cover contribute to greenhouse gas emissions.


What’s next — But not all hope is lost, the researchers say. Scientists can use this study to launch “the next frontier” of research and confirm whether or not humans altered the planet in the way they suspect, Flantua says.

Ultimately, these findings should compel us to act urgently in the face of the current climate crisis, Overpeck says. We still tear down forests — increasing vegetation change — and contribute to greenhouse gas emissions that are eroding our future survival on planet Earth.

He offers two immediate actions that humans should take:

  • First: reduce greenhouse gas emissions immediately.
  • Second: we need to undertake better forest management.

“To be successful in using existing, as well as new forests for natural atmospheric carbon reduction, we must first and foremost greatly accelerate greenhouse gas emissions reductions, primarily by halting the burning of fossil fuels,” he says.

If we don’t curb our greenhouse gas emissions, it won’t matter how many new trees we plant, Overpeck says.

“If this isn’t the top priority, climate change will only continue and stress trees and forests even more,” he says.

Forests are the places where the greatest vegetation loss and greenhouse gas emissions are occurring. This doesn’t mean reflexively “raking” forest floors, as former President Trump once suggested.

Instead, it means “we need to start managing forests, whether new or old, proactively for change,” Overpeck says. That means planning for the long-term protection of forests and the essential ecosystem services they provide, including habitat biodiversity and recreational use.

With these next steps in hand, perhaps we can halt the patterns of devastation that humans have been inflicting on the planet for centuries — and likely thousands — of years.

Abstract: Global vegetation over the past 18,000 years has been transformed first by the climate changes thataccompanied the last deglaciation and again by increasing human pressures; however, the magnitude and patterns of rates of vegetation change are poorly understood globally. Using a compilation of 1181 fossil pollen sequences and newly developed statistical methods, we detect a worldwide acceleration in the ratesof vegetation compositional change beginning between 4.6 and 2.9 thousand years ago that is globally unprecedented over the past 18,000 years in both magnitude and extent. Late Holocene rates of change equal or exceed the deglacial rates for all continents, which suggests that the scale of human effects on terrestrial ecosystems exceeds even the climate-driven transformations of the last deglaciation. The acceleration of biodiversity change demonstrated in ecological datasets from the past century began millennia ago
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