DAVID TILMAN, a Fellow of the American Academy since 1995, is Regents Professor
and McKnight Presidential Chair in the College of Biological Sciences and Director
of the Cedar Creek Ecosystem Science Reserve at the University of Minnesota. He
is also a Professor at the Bren School of Environmental Science and Management at
the University of California, Santa Barbara. He is the author of Functional Consequences
of Biodiversity: Empirical Progress and Theoretical Extensions (with Ann
P. Kinzig and Stephen Pacala, 2002), Plant Strategies and the Dynamics and Structure
of Plant Communities (1988), Resource Competition and Community Structure
(1982), and more than two hundred scientific papers.
The world is about to be full. Within two or three generations, our global population
– currently seven billion people – will level off between ten billion
and eleven billion. Although humanity steadily increased in size as it spread from
Africa across the habitable lands of Earth, it was not until the 1920s that this
growth turned explosive. In 1850, the global population was 1.1 billion people,
on a trajectory to double every one hundred fifty years. This low growth rate held
until World War I, after which the emergence of modern medicine and sanitation led
to increasingly rapid annual growth rates. When this rate hit its peak in 1970,
the global population was on course to double every thirty-five years. Now, our
population growth rate – though still positive – is steadily slowing
as we approach our maximum Earth density.
What will life be like on a full Earth? Can we provide eleven billion people with
a secure supply of nutritious foods? Is it even possible for so many people to live
on Earth without destroying its remaining natural ecosystems? Agriculture already
accounts for more than 25 percent of global greenhouse gas emissions and occupies
55 percent of Earth’s ice and desert-free land area. Can we feed up to eleven billion
people and still maintain a livable climate? Will the ethics, customs, rights, and
laws established when the world had one billion or fewer people adequately guide
a world that is ten times more populous? Or will new ethical principles be needed
to live sustainably in this new context?
The answers to these and related questions must also consider a second major way
we fill Earth: our consumption. Many, but by no means all, of the less-developed
nations of the world have rapidly growing economies. Based on current growth trajectories,
citizens in developing nations are likely to gain three to five times more buying
power within the next forty years. This is a continuation of a trend that began
in earnest in the early 1900s: from 1900 to 2000, the buying power of the typical
person on Earth increased 360 percent, while the global population increased 270
percent. What might the totality of global consumption look like in 2050?
Consider the World Bank forecasts of the global economy and the United Nations projections
of the global population. Per capita inflation-adjusted incomes are on a trajectory
to increase 140 percent from 2000 to 2050, while the global population should increase
50 percent. The cumulative effect of these global increases is a 260 percent increase
in consumer buying power between 2000 and 2050. Urbanization also accompanies economic
growth: in 1960, slightly less than one billion people lived in cities. By 2013,
more than 3.5 billion people were urban. By the time that the great human expansion
reaches its limit, the vast majority of the peoples of the world will be living
in large cities and have incomes associated with middle-class lifestyles.
Because incomes determine how much an individual can consume, the full environmental
impact of nine billion people in 2050, or ten to eleven billion by the end of the
century, will be much greater than is suggested by the increase in population alone.
Moreover, greater consumption does not necessarily lead to better lives. This is
especially true for food. The world’s two billion overweight or obese people would
likely be harmed, rather than benefit, from increased caloric consumption. Indeed,
increasing global incomes and urbanization are strongly associated with dietary
and lifestyle shifts that degrade health. However, the world’s eight hundred million
malnourished people would greatly benefit from increased incomes and better diets.
The future of humanity, including our ability to live on Earth in ways that would
allow future generations to enjoy a quality of life at least as high as ours, will
depend on the decisions we make in the coming decades. These decisions will impact
our diets, our health, and the abilities of managed and natural ecosystems to supply
us with vital services, and will also determine how many other species will share
the planet with us. Some of these decisions will be pragmatic; others will be ethical.
The world faces many unavoidable tradeoffs. Actions that provide a net benefit
or profit to one individual, such as a farmer applying more fertilizer to cropland
to increase yields, may come at a cost to the environment and to the health of others.
On a full Earth, the actions of any one person are likely to impact the well-being
of someone else; just as the actions of any one nation may impact all other nations.
The essays in this issue of Dædalus address issues related to agriculture,
diets, health, and the environment, as well as the ethics and value systems needed
to assure equity and well-being within each generation and across all future generations.
Our essays begin with a broad overview of the current environmental impacts of agriculture,
how growth in incomes and population will influence the future of the environment,
and how these environmental impacts may be avoided. In doing so, my essay with coauthor
Michael Clark also briefly touches on many of the themes developed in depth in the
rest of this volume.
Catherine Bertini highlights the central role that women play as the primary providers
of food in most of the world, as well as their need for equity and voice if, especially
in the developing world, women are to be empowered to solve malnutrition, children’s
health, and other major problems related to food, diet, and agriculture. The essay
by Jaquelyn Jahn, Meir Stampfer, and Walter Willett is an informative and insightful
synthesis of decades of research on nutrition and health, addressing such global
problems as undernutrition, obesity, and diet-dependent metabolic imbalances that
lead to noncommunicable diseases such as diabetes and heart disease.
The next three essays all address agriculture, its sustainability, and the environment
from different vantage points. Nathaniel Mueller and Seth Binder open the discussion
with quantitative analysis of the increases in global food supplies that could be
attained by intensifying agriculture in developing nations. Their analysis highlights
the social, political, and economic barriers that have kept crop yields so low in
these nations, and suggests how these might be overcome. Next, Andrew Balmford,
Rhys Green, and Ben Phalan question if such intensification indeed is the best way
to meet food demand and preserve nature, or if conservation of endangered wildlife
would be better achieved via low-intensity agriculture. G. Philip Robertson concludes
this trio by discussing if agriculture could be made sustainable and still feed
a full Earth. He does so in the context of the ethical assertion that sustainability
requires current agricultural practices not to limit the ability of future generations
to provide themselves with diets and a quality of life at least as good as exists
Our volume ends with Brian Henning’s essay on the ethics of food, biofuels, and
animal feed. His perspective as an ethicist adds a depth and nuance to all of the
preceding contributions. Who, he asks, should have the greater right to consume
the global food supply: people (who directly consume 60 percent of all crops), livestock
(which consume 35 percent) or automobiles (which consume 5 percent)? Are livestock
and cars more worthy of food than the eight hundred million undernourished people