Tipping towards the unknown

Researchers propose critical planetary boundaries, transgressing them could be catastrophic. But there is hope

Replies to criticism of the Planetary Boundaries concept:
Johan Rockström: addressing some key misconceptions

Planetary Boundaries concept is valuable for policy

New approaches are needed to help humanity deal with climate change and other global environmental threats that lie ahead in the 21st century. A group of 28 internationally renowned scientists propose that global biophysical boundaries, identified on the basis of the scientific understanding of the Earth System, can define a safe planetary operating space that will allow humanity to continue to develop and thrive for generations to come.

This new approach to sustainable development was conveyed in Nature and Ecology and Society where the scientists have made a first attempt to identify and quantify a set of nine planetary boundaries.

"The human pressure on the Earth System has reached a scale where abrupt global environmental change can no longer be excluded. To continue to live and operate safely, humanity has to stay away from critical ‘hard-wired´ thresholds in the Earth's environment, and respect the nature of the planet's climatic, geophysical, atmospheric and ecological processes," says lead author Johan Rockström, director of the Stockholm Resilience Centre.

He warns that transgressing planetary boundaries may be devastating for humanity, but if we respect them we have a bright future for centuries ahead.

Nine boundaries identified
The group of scientists including Hans Joachim Schellnhuber, Will Steffen, Katherine Richardson, Jonathan Foley and Nobel Laureate Paul Crutzen, have attempted to quantify the safe biophysical boundaries outside which, they believe, the Earth System cannot function in a stable state, the state in which human civilizations have thrived.
The scientists first identified the Earth System processes and potential biophysical thresholds, which, if crossed, could generate unacceptable environmental change for humanity. They then proposed the boundaries that should be respected in order to reduce the risk of crossing these thresholds.

The Nine boundaries identified were:
- climate change
- stratospheric ozone
- land use change
- freshwater use
- biological diversity
- ocean acidification
- nitrogen and phosphorus inputs to the biosphere and oceans
- aerosol loading
- chemical pollution.

The study suggests that three of these boundaries (climate change, biological diversity and nitrogen input to the biosphere) may already have been transgressed. In addition, it emphasizes that the boundaries are strongly connected — crossing one boundary may seriously threaten the ability to stay within safe levels of the others.

See video with Johan Rockström introducing the planetary boundaries (article continues below).

Humans behind change
The scientists emphasize that the rapid expansion of human activities since the industrial revolution has now generated a global geophysical force equivalent to some of the great forces of nature.
"We are entering the Anthropocene, a new geological era in which our activities are threatening the Earth's capacity to regulate itself. We are beginning to push the planet out of its current stable Holocene state, the warm period that began about 10,000 years ago and during which agriculture and complex societies, including our own, have developed and flourished, "says co-author Professor Will Steffen, co-theme leader and Director of the ANU Climate Change Institute, Australian National University.

"The expanding human enterprise could undermine the resilience of the Holocene state, which would otherwise continue for thousands of years into the future, "he says.

Drifting away from a familiar domain
Co-author Professor Hans Joachim Schellnhuber points out that the climate system has clearly started to drift away from the familiar domain where historic experiences apply. The risk of highly nonlinear changes in our environmental conditions is sharply increasing outside that domain.

- Observations of an incipient climate transition include the rapid retreat of summer sea ice in the Arctic Ocean, melting of almost all mountain glaciers around the world, and an increased rate of sea-level rise in the last 10-15 years, Professor Schellnhuber says. He is Director of the Potsdam Institute for Climate Impact Research.

- A novel framework
The planetary boundaries concept is already gaining popular interest outside the scientific community, and will be the subject of an upcoming book by environmental author Mark Lynas, whose previous climate change book Six Degrees won the Royal Society prize in 2008.

Katherine Richardson, co-author of the scientific article, emphasises the huge potential for mankind to be more proactive and prevent us doing irreparable damage to the environment.

- What we now present is a novel framework through which our scientific understanding of the Earth System can potentially be used more directly in the societal decision making process, says Richardson. She is Professor at the Earth System Science Center at the University of Copenhagen.

Safe within boundaries
The researchers stress that their approach does not offer a complete roadmap for sustainable development, but does provide an important element by identifying critical planetary boundaries.

- Within these boundaries, humanity has the flexibility to choose pathways for our future development and well-being.  In essence, we are drawing the first — albeit very preliminary — map of our planet´s safe operating zones.  And beyond the edges of the map, we don´t want to go.  Our future research will consider ways in which society can develop within these boundaries — safely, sanely and sustainably, says co-author Professor Jonathan Foley, Director of the Institute on the Environment at the University of Minnesota.

See video with Professor Foley, explaining the boundaries and the importance of not transgressing them.

Conceptual description of planetary boundaries: In (a) the boundary is set to avoid the crossing of a critical threshold in an Earth System process (precise position uncertain). In (b) there is no known global threshold effect, but exceeding the boundary will likely cause a large number of undesired effects of serious concern for humanity.