Planetary boundaries

Planetary boundaries

What is the concept of planetary boundaries and how does it relate to sustainability?

Anthropogenic pressures on the Earth System have reached a scale where abrupt global environmental change can no longer be excluded. A new approach is proposed to global sustainability in which planetary boundaries are defined, within which it is expected that humanity can operate safely. Transgressing one or more planetary boundaries may be deleterious or even catastrophic due to the risk of crossing thresholds that will trigger non-linear, abrupt environmental change within continental- to planetary-scale systems. There are nine planetary boundaries and, drawing upon current scientific understanding, quantifications are proposed for seven of them. These seven are:

  • climate change 
  • ocean acidification 
  • stratospheric ozone 
  • biogeochemical nitrogen (N) cycle and phosphorus (P) cycle 
  • global freshwater use 
  • land system change 
  • the rate at which biological diversity is lost 

The two additional planetary boundaries for which a boundary level has not been determined are chemical pollution and atmospheric aerosol loading. It is estimated that humanity has already transgressed three planetary boundaries: for climate change, rate of biodiversity loss, and changes to the global nitrogen cycle.

Planetary boundaries are interdependent, because transgressing one may both shift the position of other boundaries or cause them to be transgressed. The social impacts of transgressing boundaries will be a function of the social-ecological resilience of the affected societies. These proposed boundaries are rough, first estimates only, surrounded by large uncertainties and knowledge gaps. Filling these gaps will require major advancements in Earth System and resilience science. The proposed concept of "planetary boundaries" lays the groundwork for shifting our approach to governance and management, away from the essentially sectoral analyses of limits to growth aimed at minimizing negative externalities, toward the estimation of the safe space for human development. Planetary boundaries define, as it were, the boundaries of the "planetary playing field" for humanity if we want to be sure of avoiding major human-induced environmental change on a global scale.

Planetary boundaries diagram

When dealing with the concept of planetary boundaries in a more generic sense, it is important to consider the impacts and effects of population and demographics.

Population

Population provides an important contextual reference on sustainable development for decision makers looking at the interrelationships between people, resources, the environment and development.  Population change is a significant signal as countries try to reduce poverty, achieve economic progress, improve environmental protection, and move to more sustainable consumption and production.  More stable levels of fertility can have a considerable positive impact on quality of life.  In many countries, slower population growth has bought more time to adjust to future population increases.  

Urbanization has become a dominant trend in the growth and distribution of the population.  Rapid population growth and migration can lead to unsustainable living conditions and increased pressure on the environment, especially in ecologically-sensitive areas.  The search for better living conditions in urban areas reflects rural unemployment and underemployment; poor rural social services; unavailability of arable land; natural disasters, particularly drought; and civil unrest.  It implies the need for more effective programmes to support rural development.  The informal urban settlements that often develop are precarious and marginal. They tend to lack basic services and tenure security; are located in areas predisposed to natural disasters; and are characterised by poverty, inadequate health and education facilities, and high crime rates.

Demographics

The growth of world population and production combined with unsustainable consumption patterns places increasingly severe stress on the life-supporting capacities of our planet. These interactive processes affect the use of land, water, air, energy and other resources. Rapidly growing cities, unless well-managed, face major environmental problems. The increase in both the number and size of cities calls for greater attention to issues of local government and municipal management. The human dimensions are key elements to consider in this intricate set of relationships and they should be adequately taken into consideration in comprehensive policies for sustainable development. Such policies should address the linkages of demographic trends and factors, resource use, appropriate technology dissemination, and development. Population policy should also recognize the role played by human beings in environmental and development concerns. There is a need to increase awareness of this issue among decision makers at all levels and to provide both better information on which to base national and international policies and a framework against which to interpret this information.

There is a need to develop strategies to mitigate both the adverse impact on the environment of human activities and the adverse impact of environmental change on human populations. The world's population is expected to exceed 8 billion by the year 2020. Sixty per cent of the world's population already live in coastal areas, while 65 per cent of cities with populations above 2.5 million are located along the world coasts; several of them are already at or below the present sea level.

Key questions for this area

If you are studying or teaching planetary boundaries, population or demographics, or are looking to add content to your unit, the following are some key questions you should be able to answer and/or consider:

  • Are there any other models that exist to give meaning to planetary boundaries?
  • Which countries are dealing with slowing population growth? What impact does a slowing population rate have on sustainable development?
  • How does differing demographics impact on achieving sustainability?

Useful resources 

If you are interested in finding out more about this topic, check out our resources for inspiration.

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