Human Race Has Changed North America More Than Last Ice Age, Say Scientists

A new study suggests humans have changed North America more substantially than the last Ice Age.
Brad Bergan

Human use of land and fossil fuel extraction have wrought unspeakable levels of ecological damage — exacerbating global climate change and hastening the loss of biodiversity — but new research shows the scale of global change the human race has caused is greater than that of an ice age, according to a recent study published in the journal Science.


Human race changed North America more than last Ice Age

Roughly 11,700 years ago, the 2.5-million-year Pleistocene epoch came to an end. The planet's most recent Ice Age happened in this epoch, when glaciers reached across vast swaths of the planet. When it came to an end, North American ecosystems entered a phase of rapid change, where forests and grasslands sprouted throughout the continent, ushering in a new era.

The 12,000 years since are less than the blink of an eye compared to the 4.57-billion-year age of the Earth. Most geological epochs carry on for several million years, but for the last decade, scientists have said the last 250 years have seen humans usher a new epoch: the Anthropocene.

New research presented at this month's annual meeting of the Ecological Society of America (held virtually) solidified the Anthropocene theory, reports Gizmodo. It shows how in the last 250 years, human land use altered North American landscapes on an even grander scale than the recession of mile-thick glaciers 12,000 years ago.

"This puts our modern world in context, and it shows that these changes are really unprecedented," said Stanford University paleoecologist M. Alisson Stegner, who led the recent study, to Gizmodo.

Pleistocene saw 10 abrupt environmental shifts across 100 sites every 250-year period

To understand these ecological changes, the researchers analyzed fossil records spanning hundreds of years from the global Neotoma Paleoecology Database. They observed shifts in fossilized pollen records recognized in sediment cores and found which kinds of vegetation lived in varying locations throughout North America at different times.

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Specifically, they looked for signs of sudden, system-wide transitions, like when grasslands transform into forests, or when an oak forest shoots out of what was initially a spruce forest.

Researchers explored how pollen records shifted over 250-year-long periods, and saw an average of 10 sudden shifts across 100 sites during every 250-year stretch that together comprises the entire Pleistocene.

Fossil fuels, agriculture, and pollution are major players

This is a colossal amount of rapid change, but even more change came after humans made the scene. Between 1700 and 1950, the researchers observed 20 sudden changes per 100 sites, reports Gizmodo.

While they've yet to narrow down what specific activities drove each rapid shift, the scientists saw a strong indication that agriculture, logging, pollution, fishing, and the ongoing extraction of fossil fuels have played major parts in the growing state of calamity that is the climate crisis. However the distribution of causes plays out, their new findings suggest human activity has changed the face of North American ecosystems more than the last Ice Age.

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