William E. (Bill) Rees, PhD, FRSC, is a Canadian human ecologist, ecological economist and Professor Emeritus at the University of British Columbia in Vancouver, Canada, where he taught and conducted interdisciplinary research for more than four decades. He is perhaps best known for co-developing the ecological footprint concept and method of analysis with his graduate students. This quantitative tool estimates humanity's demand on nature, through measurable flows of energy and materials to and from ecosystems; it thus reinforces associated concepts such as ecological limits and biocapacity, and shows clearly that the human enterprise is in a state of advanced ecological overshoot.
Rees' work has long focused on the relationship between the human enterprise and the ecosphere, sustainability, human carrying capacity, over-exploitation, ecological overshoot, and urban systems and on cognitive barriers to understanding the depth of our eco-predicament. He has authored or co-authored hundreds of peer-reviewed papers and popular articles on these issues. His work is taken up by governments, nongovernmental organizations, educators, and scholars internationally. Rees has been a member of various sustainability-oriented organizations, including the Canadian Society for Ecological Economics (co-founder and past-president), OneEarth Living (co-founder), the Post Carbon Institute, and the Club of Rome.
Rees' contributions are widely recognized. He was elected a Fellow of the Royal Society of Canada and received a Pierre Elliott Trudeau Foundation Fellowship. Honours include the Blue Planet Prize (shared with his former student Mathis Wackernagel), the ISEE Kenneth Boulding Award for Ecological Economics, the Herman Daly Award, and an honorary doctorate from Université Laval.
He also held senior administrative roles at UBC, including Director of the School of Community and Regional Planning (SCARP).
Background Background / Youth
William E. (Bill) Rees was born on December 18, 1943, in Brandon, Manitoba, Canada, and spent his early childhood in Montreal, Quebec, and later in Toronto, Ontario. Many of his most formative experiences took place on his grandparents' farm in southern Ontario, where he began to experience and understand humans as a species within many ecosystems. With various cousins, Rees worked the market garden, picked apples, fed and "dusted" the chickens, pitch-forked hay onto a horse-drawn wagon, and went fishing when the day's work was done.
On one occasion after the day's exertions, a ten-year old 'Billy' was sitting at his Grandmother's dinner table, staring absently at the food heaped on his plate. "My subconscious must have been grinding away because it suddenly struck me that I had had a hand in raising everything I was about to eat. Trivial observation? Perhaps, but with it came an unexpected rush of emotion including a profound insight. I knew deep in my bones that farm work and food made me a product of sun and soil. I acquired a very personal understanding that we are, quite literally, what we eat. No science there. This was the experience of raw truth, my personal epiphany."
Since then, Rees has been concerned that few young people today have an opportunity to be "up close and personal" with the ecosystems that support them – and thus have never come to feel "in their bones" that they are part of nature.
Undergraduate studies
Rees first earned an undergraduate degree (B.Sc.) in Zoology from the University of Toronto. This foundational study of animal biology and ecosystems provided the groundwork for his later explorations of human ecology, carrying capacity and biophysical limits.
Ph.D in Population Ecology (University of Toronto)
Continuing his education with a scholarship to the University of Toronto, Rees earned his Ph.D. in population ecology. His fieldwork and academic courses equipped him with the conceptual and analytical tools to study population dynamics in relation to biocapacity, inter- and intra-specific competition, the interplay of positive and negative feedback, and how these factors ultimately impose limits on population and material growth. It also infused him with a lasting fascination with society's general ignorance of the biophysical foundations of its own existence. Thus equipped, Rees joined the University of British Columbia (UBC) in September 1969, initially with a joint appointment as assistant professor in the School of Community and Regional Planning (SCARP) and the (former) Institute of Animal Resource Ecology.
Early academic Experience
Rees was assigned the task of developing an "ecological planning" stream in SCARP, beginning with courses on the ecological basis for planning and on ecological land-use planning. His early research focused on the application of environmental impact assessment in Canada, but his background in ecology helped him maintain his broad interest in the biophysical requirements for human sustainability.
Shortly after joining UBC, Dr. Rees was appointed to an interdisciplinary committee tasked with establishing the parameters for a proposed new water-oriented research centre. He was asked to explain his research interests and potential contribution to the new centre. Rees presented a seminar to the committee on human carrying capacity and the relevance of the concept to water resource management. A senior colleague (one of Canada's foremost resource economists) later took him aside and warned him that, should he pursue this line of research, his career at UBC would be a Hobbesian "nasty, brutish and short." Apparently, economists had negated the concept of carrying capacity as applied to Homo sapiens.
This was Rees' introduction to the assumptions of neoliberal economics that the human enterprise operates separately from, and largely independent of, nature. His economist colleague told him that "human ingenuity (read 'technology') is the greatest resource" and that any residual local resource limits could be overcome through trade, at least until technology came to the rescue.
Despite this initial discouragement, Rees continued to dwell on the humanity-nature connection, convinced that the material assumptions of neoliberal economic theory were deeply flawed. This instinct was buoyed by the early ecology-oriented publications of renegade economist Herman Daly, one of the fathers of ecological economics (and who subsequently became a collaborator and friend). Rees was encouraged enough to develop a special focus on the material ecology of modern cities. He came to view them as massive "dissipative structures" that can be sustained only by the continuous consumption/dissipation of low-entropy energy and matter and the production of entropic waste. This urban metabolism makes cities essentially parasitic on the ecosphere; at best, they are the eco-dependent consumptive components of the total human ecosystem and thus highly vulnerable to adverse global change. People are generally unaware that the bio-productive components of human urban ecosystems are actually rural hinterlands, increasingly dispersed across the planet by trade. He would ask his urban planning students: "What would happen to a city's millions of inhabitants if cut off from their supportive ecosystems?" Instead of viewing human settlements as isolated from nature, his research began to map the massive, unseen flows of energy and materials extracted from the ecosphere and required to sustain urban populations, as well as the equal flow of useless waste injected back into the ecosphere. This ecological framing – seeing cities and human economies as wholly embedded sub-systems of the biosphere – set the stage for Rees' articulation of the ecological footprint concept.
Academic career
William E. Rees was initially jointly appointed as Assistant Professor in the University of British Columbia's School of Community and Regional Planning (SCARP) and UBC's Institute for Animal Resource Ecology in September 1969. He was promoted to Associate Professor (1976) and Professor (1990), and became Professor Emeritus following his official retirement from UBC in 2012.
Rees taught 15 different courses at UBC from 1969–70 until his retirement in 2011–12. His long-running and interdisciplinary offerings spanned planning practice, environmental assessment, human ecology, and ecological economics. Courses included: Environmental Assessment; Ecological Basis of Planning; Urban Land-use Planning and Economic Change; Resource Analysis for Regional Planning; Enviro-Economic Systems (ecological economics); and Regional Planning Workshop, as well as graduate colloquia including an advanced workshop on Global Change, Complexity, and Panarchy.
Rees' research and teaching originally focused on project assessment and the biophysical prerequisites for sustainability in an era of accelerating ecological change. He developed a special interest in cities and in ecologically relevant metrics of urban sustainability, including urban ecological footprint analysis. These pursuits led to explorations of complexity theory, human socio-behavioural ecology, and beyond.
As of 2026, Rees remained Professor Emeritus at UBC. His most recent interests and publications explore the role of human evolution in the emergence of the contemporary (un)sustainability crisis. What are the neurobiological, cognitive, and cultural barriers to sustainability? How can we account for humanity's well-developed capacity for self-delusion? Rees has authored or co-authored hundreds of peer-reviewed papers, book chapters, and numerous popular articles on the above and related topics.
Active across disciplines, Rees was/is a long-term member of the Global Ecological Integrity Group, a fellow of the Post Carbon Institute, a founding member and past president of the Canadian Society for Ecological Economics, and co-founder of OneEarth Living, a nonprofit "think and do tank" advancing sustainable everyday living around the world. The influence of Rees' work is recognized and awarded. Rees has been invited to lecture on areas of his expertise across Canada and the United States, as well as in Mexico, many European countries, Australia, China, Thailand, Malaysia, Sri Lanka, Indonesia, Japan, South Korea, Brazil, Ecuador, and the former Soviet Union.
Within UBC's SCARP, Rees held various senior administrative roles, including Director (1 January 1994 – 30 June 1999). Later, he served as Associate Director of SCARP and the Centre for Human Settlements (2007–2009). Rees also contributed to departmental and university governance. Documented roles include chairing the SCARP Ph.D. Admissions Committee and as a member of UBC's Senior Appointments Committee (2002–2006), and a committee formed to define an undergraduate program in sustainability studies (1998–2000).
Research Focus Sustainability science generally
Rees' scholarly contributions examine the biophysical requirements for, and natural constraints on, industrial civilization, including the implications of the growing human ecological footprint for resource and public policy planning. He explores the question: "How can we integrate ecological constraints into planning and policy, given that mainstream economic logic practically ensures that human demand will exceed ecosystems' regenerative, assimilative capacities?" A key interest is in the role of energy in the expansion/sustainability of the human enterprise. Rees' research and teaching also explore the socio-cultural and human behavioural barriers to the sustainability transition. He wonders why high intelligence (e.g., the capacity for logical thought and reasoning from the evidence) plays such a small role in societal decision-making, particularly pertaining to sustainability.
Ecological overshoot