Nature Special: Planetary Boundaries - Limits of the Earth

To avoid catastrophic environmental change humanity must stay within defined 'planetary boundaries' for a range of essential Earth-system processes, argue Johan Rockström and his co-authors in a Nature Feature. If one boundary is transgressed, then safe levels for other processes could also be under serious risk, they caution. Seven expert commentaries respond to this proposal in Nature Reports Climate Change.


The inner green shading in the above figure represents the proposed safe operating space for nine planetary systems. The red wedges represent an estimate of the current position for each variable. The boundaries in three systems (rate of biodiversity loss, climate change and human interference with the nitrogen cycle), have already been exceeded.

Planetary Boundaries

Identifying and quantifying planetary boundaries that must not be transgressed could help prevent human activities from causing unacceptable environmental change, argue Johan Rockström and colleagues in A safe operating space for humanity in Nature.

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.

Nine boundaries were identified including climate change, stratospheric ozone, land use change, freshwater use, biological diversity, ocean acidification, nitrogen and phosphorus inputs to the biosphere and oceans, aerosol loading and 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.

The Road To Copenhagen

In December this year, parties to the United Nations Framework Convention on Climate Change (UNFCCC) will descend on Copenhagen to wrangle over the details of a new global climate deal — a potential successor to the Kyoto Protocol.

As the world moves along the road to Copenhagen, Nature will be covering every aspect of the science and politics of climate change in articles that will be collected here.