Concerns of natural and social scientists, policymakers and lay people about whether the Earth can continue to support human population growth as well as economic prosperity has led to the development of the field of sustainability science and world jamborees such as The United Nations Conference on Sustainable Development (Rio+20). Largely missing from sustainability science and the discussions in Rio de Janeiro are the key ecological principles that govern life on Earth, argue researchers at UNM and the Santa Fe Institute.

Sustainability science is an emerging field of research that takes into account the interactions between natural and human systems. These interactions are central to the goal of sustainability: to meet the needs of present and future generations while reducing poverty and conserving the planet's life support systems.

Twenty years ago world leaders met at the United Nations Earth Summit in Rio de Janeiro to discuss concerns over rising income inequality, environmental destruction, and unchecked human population growth. They called for a radical shift in how nations approach economic development. Now, world leaders converge once again in Rio de Janeiro to assess progress toward sustainable development.

About 20 years ago, the field of Macroecology also began to emerge with a publication in Science by James H. Brown, Distinguished Professor of Biology at the University of New Mexico, and Brian A. Maurer, currently a Professor at Michigan State University. Macroecology examines relationships between organisms and their environments at large spatial scales to characterize and explain ecological patterns of abundance, distribution and diversity. Now, Brown and colleagues are applying this approach to understand the past, present and future of human civilization and the implications for sustainability.

In conjunction with Rio+20, the open-access journal PLoS Biology is publishing three articles by leaders in ecology and conservation science. These papers raise, once again, important concerns about biophysical limits to human population and economy that should be a major topic at the conference—but apparently will get little attention. One of the articles, by the Human Macroecology Group—a collaboration among scientists from several institutions in northern New Mexico—is titled, "The Macroecology of Sustainability".

The team of researchers argue that "a macroecological approach to sustainability aims to understand how humans are integrated into and constrained by the Earth's systems at multiple spatial and temporal scales," and that "any efforts to develop a science of sustainability or implement policy solutions are necessarily incomplete and will ultimately fail without considering the core ecological principles that govern all of life."

"Human macroecology is the study of the interactions between humans and their physical, biological and social environments at multiple spatial and temporal scales," said Robbie Burger, a PIBBS Fellow in the UNM Department of Biology and lead author of the paper. "From this perspective, humans are no different than any other species. We are constrained by the same physical laws and governed by the same biological principles that regulate the millions of populations of other plants, animals, and microbes on the planet."

The researchers highlight three principles that should be central to sustainability science including: physical conservation laws govern the flows of energy and materials between human systems and the environment; smaller systems are connected by these flows to larger systems in which they are embedded; and global constraints ultimately limit flows at smaller scales.

Burger, Brown and colleagues use a series of case studies to illustrate the how processes at larger scales impact of what appear to be locally ‘sustainable' systems. They show how decreasing per-capita consumption of petroleum, fresh water, arable land, metals, phosphate, fish and wood at the global scale indicates that the growing human population and economy have surpassed the Earth's capacity to support even current levels of population and socioeconomic activity, let alone future trajectories.

"Our analyses and reports by other leading scientists demonstrate that we are near or have surpassed peak production of many essential resources," emphasized Burger, "it's going to become more and more difficult for human ingenuity to provide solutions to these problems now that we are pushing the limits of the biosphere."

"If you get the best data available and do the math it becomes clear that our trajectories are unsustainable," added Brown, "we've created a huge bubble of population and economy. It has to be deflated or it's going to burst."

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