The authors have declared that no competing interests exist.
Ecological principles must govern sustainability, yet sustainability science is largely concerned with social-environmental interactions and barely considers physical limits on resource use. Whether it is possible to overcome such limits can be contested, but the issues raised by a macroecological perspective should be a fundamental part of the United Nations Conference on Sustainable Development (Rio+20).
The United Nations Conference on Sustainable Development (Rio+20) takes place in Rio de Janeiro on 20–22 June 2012. Twenty years after the 1992 Earth Summit that led to the establishment of two major environmental conventions (the United Nations Framework Convention on Climate Change and the Convention on Biological Diversity), Rio+20 presents an opportunity for the leaders of the world's governments to re-examine their commitments to sustainable development. An Essay by Burger et al.
Burger et al.
This discussion is not new. Two issues have continued to be debated over the 20 years since the first Rio Earth Summit. One concerns the concept of sustainability and what it means in practice. A common query that has no easy answer asks about the sustainability of what, for whom, where, and over what time scales? Endless rhetoric about sustainable consumption and sustainable development hardly ever confronts the reality that, in most cases, what is sustainable for one sector of human society at one time and place rarely has no impact on other resources, or on environmental processes separated in time and space. The second theme, now discussed for over 40 years, is about the limits to growth. Any sensible person will agree that growth cannot continue indefinitely in a finite world. Yet over recent decades, the evidence indicates continuing growth, often at close to exponential rates in both population and consumption. How is this possible? Are we borrowing from the future, are we using resources that are far from their limits, or are we adapting creatively through innovation and technologically driven efficiency and replacement? Or, are we actually failing to act responsibly given evidence that certain limits are dangerously close, or even are already transgressed?
Burger et al. present the argument for macroecological limits based on three inter-related themes and the evidence behind them. First, they describe how the flow of resources from the environment to support human societies must conform to physical laws concerning matter and energy. Therefore, at any spatial scale, flows of energy and nutrients for production and growth must come from somewhere, and a positive balance in one context will be felt as a negative balance somewhere else. Since smaller human systems (e.g., in towns and villages) are embedded in larger environmental systems, these flows and fluxes eventually add up to the global scale, where the finite nature of the biosphere and earth system must ultimately set limits. In fact, for the systems and resources that Burger et al. examine, there is evidence that we may already be reaching these limits. In the case of what is clearly a well-managed salmon fishery, resource flows have significant impacts on other components of the ecosystems (e.g., reduced resources for predators or decomposers). In what is an apparently sustainable urban system, the environmental costs to the surrounding landscape or on ecosystems elsewhere are shown to be substantial. In showing how per capita consumption of many materials and resources is now declining, Burger et al. suggest that their data may be the first evidence that we are approaching limits for some resources such as phosphorous, arable land, and freshwater. Some of this decline may be due to efficiencies, redundancy, and technological replacement of resources by innovative human societies, as Matthews and Boltz describe, but they agree that, ultimately, global constraints exist.
There is no doubt that these are critical issues for the environmental sciences to address. The research questions are difficult to pin down because they are embedded in a complex nexus of issues where ecological and evolutionary sciences, natural resource management, poverty alleviation, equitable and sustainable growth, individual rights and responsibilities, and the governance of the environment all converge. The academic community is increasingly engaged in defining the agenda for new science that will be needed. For example, following the recent Planet under Pressure meeting held in London, scientists sent a declaration to the Rio+20 conference
The difference between ecological pessimism in Burger et al. and technological optimism in Matthews and Boltz is only one of the many ways that the problem can be viewed. Often the focus needs to be on extremes, or on non-linearities and irreversibilities in environmental systems that do not sit easily in standard economic analysis
Sustainability science therefore needs much stronger connections with environmental sciences, including macroecology. Green economies, a major focus for Rio+20, similarly need to be embedded in ecological principles and not simply be focused on economic growth based on new, greener production systems. Hopefully, in another 20 years, we can celebrate successful outcomes from the emergence of this integrated science for the environment and people.