Three centuries ago, humans were intensely using just around 5 percent of the Earth’s land. Now, it’s almost half.
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| Source: ecotope.org (David H. Montgomery / CityLab) |
Environmental scientist Erle Ellis has studied the impact
of humanity on the Earth for decades, with a recent focus on
categorizing and mapping how humans use the land—not just now, but in
the past. And his team’s results
show some startling changes. Three centuries ago, humans were intensely
using just around 5 percent of the planet, with nearly half the world’s
land effectively wild. Today, more than half of Earth’s land is
occupied by agriculture or human settlements.
“Climate change is only recently becoming relevant,” said
Ellis, a professor at the University of Maryland, Baltimore County. “If
it keeps going how it is, it will become the dominant shaper of ecology
in the terrestrial realm, but right now the dominant shaper of ecology
is land use.”
In contrast to the typical division of the world into ecological “biomes,” Ellis and his team at the Laboratory for Anthropogenic Landscape Ecology map what they call “anthromes,” or “anthropogenic biomes.” These show the intersection of ecology and human land use.
Using a range of sources, Ellis’s team mapped out that land
use, dividing the planet into grids and categorizing each cell based on
how many people lived there and how they impacted the land. The densest
areas were cities and towns, followed by close-packed farming villages.
Less populated areas were categorized by their dominant land use—crops,
livestock pasture, or inhabited woodlands—while other areas were marked
as largely uninhabited. (See image Land use, above.)
Even
with only one snapshot per century, the animation makes some of the
trends obvious. Large swaths of Russia and the United States become
cropland over the 19th century, while livestock occupies increasing
amounts of previously semi-wild land in Africa and Asia.
“Asia is pretty much the dominant transformed area, and
transformed the earliest,” Ellis said. “Europe is also pretty dense ...
The rest of the world has a different trajectory. Much slower, less
dense.”
All of this is a mixture of estimates and approximations.
One reason Ellis and his team only looked every hundred years and
divided the world into cells that stretch for miles was to avoid giving a
false impression of precision.
People
ask Ellis, “‘What was my backyard like?’” he said. “Well, we don’t have
any solid evidence … The further back in time you go, the more you have
to consider [this], in a sense, educated guesswork.”
Even more recent data can have issues, based on political
decisions that countries make about how to self-classify their land.
Saudi Arabia, for example, reports “almost every part of their country
as being rangeland” even though much of that arid land is seldom if ever
grazed.
Significant portions of the world, both now and in the
past, have been what Ellis’s team terms “seminatural.” These are
areas—frequently forests—with low but real human habitation. This could
reflect a large cell of the grid that has a farming village or two but
mostly natural forests. But frequently, Ellis says, humans have taken a
much bigger role in shaping seemingly natural wilderness than people
think.
Take
the “pristine myth”—the idea that the Americas before European
colonization were dominated by pristine wilderness untouched by human
hands. In fact, modern researchers believe that indigenous tribes had
actively shaped their landscapes through agriculture and regular burning
of American forests.
Because of this, the devastating spread of epidemics among
indigenous populations after 1492 also had a huge impact on climate—and
not just locally. Some scholars believe disease-ravaged peoples
significantly cut back on their management of American forests, which
meant far less carbon dioxide put into the atmosphere from fires and far
more absorbed into newly grown forests. The
combination could have played a significant role in the “Little Ice
Age” that lowered global temperatures for several centuries between
around 1500 and 1850 C.E.
This kind of active land management was done not just by
sedentary populations, but by hunter-gatherers, too. This, Ellis says,
is a shortcoming in the data.
“There’s no direct mapping of hunter-gatherers’ land use in
these datasets. That’s something we’re trying to rectify now,” he said,
noting that evidence suggests even non-agricultural people have major
effects on the environment.
The data also shows the massive impact made by cities, the
most dramatic way humans transform their environment. In 1700, a
negligible portion of the Earth’s surface was covered by cities. Over
the three centuries that followed, this boomed by around 40 times.
Cities are still just half a percent of the planet’s land area, but they
have had the most dramatic increase in impact of any of Ellis’s
“anthromes.”
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| Source: ecotope.org (David H. Montgomery / CityLab) |
Densely
populated farming villages—which often have similar concentrations of
people per square mile as American suburbs—are also big, especially in
the developing world. (Ellis’s team don’t map any urban areas in the
Americas or Australia before 1900, and never apply the “villages”
category to those continents, because those areas didn’t have “histories
of intensive subsistence agriculture.”)
Huge portions of India and China are occupied by these kind
of villages. So, too, were the hinterlands around major European cities
before improvements in transportation enabled produce to be brought
from farther away. Paris, for example, used to be surrounded by suburban
“market gardens” which, historians André Jardin and André-Jean Tudesq
note, could produce five or six harvests per year and had a “virtual
monopoly of the Parisian market” for food until the second half of the
19th century.
That kind of intensive agriculture to feed a demanding
urban market is part of the huge impact that cities have on the use of
land even well outside their boundaries. Those thousands or millions of
urban dwellers aren’t producing their own food, and thus need more food
produced elsewhere in order to eat.
Ellis describes two different ways that cities impact
far-away anthromes through their demands for food—one of them
devastating to natural ecosystems, the other surprisingly beneficial.
The
first sees new land being put under the plow, as societies try to
produce more food for a growing population. This is often
low-productivity agriculture, reflecting the marginal quality of the
farmland: If it was good for farming, it would have been farmed already.
But later, as populations grow, comes an “intensification” process as
technology increases the yields on low-productivity farmland.
Agricultural expansion has a massive impact on natural
biomes, and has for millennia. But the second process, intensification,
has the potential to restore some of the natural biomes that humans
previously plowed under.
“Dense cities actually have the potential to help areas
recover, because dense populations in cities often are basically pulling
people out of the rural areas where they’re farming low-productivity
land,” Ellis said. The increased production on good land means the
marginal farmland is no longer needed.
Author Charles Mann described this process taking place in New York’s Hudson River Valley in his 2018 book, The Wizard and the Prophet.
In the late 19th century, this region was dominated by “hardscrabble
farms and pastures ringed by stone walls.” Now many of those
“hardscrabble farms” are gone. Six counties in the lower Hudson Valley
had around 350,000 people and 573,000 acres of timberland in 1875; today
those same counties have more than 1 million people but three times as
much forest.
“Many
New England states have as many trees as they had in the days of Paul
Revere,” Mann writes. “Nor was this growth restricted to North America:
Europe’s forest resources increased by about 40 percent from 1970 to
2015, a time in which its population grew from 462 million to 743
million.”
But while this intensification of agriculture is allowing
the return of nature in parts of developed countries, the first
phase—expansion—is still playing out in the developing world. Erle’s
maps show the expansion of crops and livestock into areas like Africa’s
Sahel and South America’s Amazon rainforest over the past century.
“Land transformation is the big story of biosphere
transformation so far,” Ellis said. “If you’re trying to understand how
we produced the ecology we have now, it’s the story of land-use
transformation.”
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| Source: ecotope.org (David H. Montgomery / CityLab) |
So what will a future mapmaker show for the world’s land
use in 2100? Ellis said he expects urbanization to continue, at least
doubling the share of the planet’s land devoted to urban areas over the
next century.
Similarly, he expects developed countries to see an
intensification of agriculture that enables marginal land to be returned
to the wild—a process already under way in newly developed countries
like China. Poorer countries, on the other hand, may continue to convert
marginal wild land into farmland.
“It’s only poor farmers without much investment that can
make that work,” Ellis said. “When you’re investing large amounts of
money in farm equipment and fertilizers, you don’t invest that in
marginal land.”
Much depends, however, on political, economic, and
technological changes that will unfold over the next 80 years. For
example, Ellis said, the United States has recently seen “a huge shift
from beef to chicken” in consumer demand. “That changes the kind of land
that’s in demand, from grassland to production of maize and soy.”
Among the factors that could affect the future of Earth’s land use are political decisions in Brazil, where new President Jair Bolsonaro wants to open up more of the Amazon rainforest to agriculture,
and technology, where a potential breakthrough in electrical generation
such as fusion power could enable transformative changes such as
vertical urban farming. Conservation efforts, or lack thereof, could
also impact areas of intensive agriculture in developed countries.
“The future of the biosphere… depends partly on economics,
partly on politics, but also partly on vision,” Ellis said. “It depends
on what people’s values are.”
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