Humans Have Had a More Powerful Effect on the Plant World Than the Last Ice Age


Several thousand years before power generators and vehicles first burned carbon-based minerals into heat-trapping gas, humanity had already started to transform life on the planet—and not subtly. 

Newly assembled fossil records from around the world dating back 18,000 years show that plant species began to shift 3,000 to 4,000 years ago, and that those shifts have been accelerating ever since. While the work stops short of formally attributing the variations to humanity—there’s a high technical bar for that—there is a “reasonable working inference” that human-driven change “now resembles or exceeds in rate and scope even the profound ecosystem transitions associated with the end of the last glacial period.”  

In short, we’re more potent than the ice age. 

Researchers over a decade ago observed that people have affected more than 75% of land on Earth not covered in ice. Now they better understand the depth of that change. The new study, published Thursday in the journal Science, benefitted from a century of fossilized pollen records, advanced carbon-dating techniques, and new statistical tools that allowed researchers to estimate the rate at which plant species replaced each other.

Human agriculture first emerged roughly 8,000 years ago; about four millennia later, that and other land-use interventions started leaving a global mark. The shifts in vegetation came unevenly to inhabited continents, with elevated rates of change in Europe, “particularly in areas of high present and past agricultural activity,” the authors write. In many places, the effects are cumulative, meaning that ancient land-use changes continue to affect how species come and go today. 

The overall picture of vegetation change is a complicated one, and while the study gives new clarity to humanity’s role, many other factors such as regional climate changes are also forcing species turnover. “These interactions provide evidence against single-cause attributions” of rates of change, the authors write. 

Humans Have Had a More Powerful Effect on the Plant World Than the Last Ice Age

Published alongside the vegetation study, an analysis by two additional researchers warns that the findings carry troubling implications for real and proposed efforts to control climate change by planting trees or using other natural methods of capturing carbon dioxide.

In a serious charge against recent national and private reforestation efforts, they write, “the dream of large-scale tree-planting as a substitute for direct reductions of atmospheric carbon dioxide emissions may be seriously compromised.” Many impacts of global warming are accumulating faster than scientists predicted, and with continued ecological change—including an “ongoing human assault on tropical forests,” the two U.S.-based authors write—“additional climate-driven change is also a sure bet.” 

They conclude that governments may have to abandon the goal of preserving natural lands as they once were in favor of managing them for climate-related needs. Preserving trees’ pollution-fighting potential means keeping at bay risk factors that are still poorly understood, from insect infestations and wildfire to the ecological damage from the rising temperature itself.

Pressures on plants—especially the agricultural varieties that sustain human life—are growing even as populations and consumption swell. A separate paper out this week in the journal CABI Agriculture and Bioscience estimates the phenomenal cost of pests alone to African countries. By tabulating yield losses from invasive species, plus the labor costs related to fighting them, the authors found that countries in Africa spend almost $3.7 trillion a year fighting pests—or about 150% of the continent’s gross domestic product. 

The two most destructive pests are the tomato leafminer and the fall armyworm, which respectively cause $11.4 billion and $9.4 billion in losses annually. Nigeria faces the highest losses from these and many other invasive species—more than $1 trillion a year, almost entirely in labor costs—followed by Democratic Republic of Congo at $318 billion. 

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