Vol 461 24 September 2009 FEATURE A safe operating space for humanity Identifying and quantifying planetary boundaries that must not be transgressed could help prevent human activities from causing unacceptable environmental change argue Johan Rockstr m and colleagues lthough Earth has undergone many periods of significant environmental change the planet s environment has been unusually stable for the past 10 000 years1 3 This period of stability known to geologists as the Holocene has seen human civilizations arise develop and thrive Such stability may now be under threat Since the Industrial Revolution a new era has arisen the Anthropocene4 in which human actions have become the main driver of global environmental change5 This could see human activities push the Earth system outside the stable environmental state of the Holocene with consequences that are detrimental or even catastrophic for large parts of the world During the Holocene environmental change occurred naturally and Earth s regulatory capacity maintained the conditions that enabled human development Regular temperatures freshwater availability and biogeochemical flows all stayed within a relatively narrow range Now largely because of a rapidly growing reliance on fossil fuels and A industrialized forms of agriculture human activities have reached a level that could damage the systems that keep Earth in the desirable Holocene state The result could be irreversible and in some cases abrupt environmental change leading to a state less conducive to human development6 Without pressure from humans the Holocene is expected to continue for at least several thousands of years7 Planetary boundaries To meet the challenge of maintaining the Holocene state we propose a framework based on planetary boundaries These Climate change Oc ean ac id i t ca Ch e ot m ye n tio llu ed po nti l ica qua t SUMMARY New approach proposed for defining preconditions for human development Crossing certain biophysical thresholds could have disastrous consequences for humanity Three of nine interlinked planetary boundaries have already been overstepped s o Bi ers div Nitro g cycl en e P ho bio s g cy pho ow eoch b ou emi cle ru nd ca ar l y loss ity tospheric Stra epletion ne d ozo Atmosphe r aerosol load ic in not yet quant g i ed n ion bal Glo er use at shw fre Change in lan d us e Figure 1 Beyond the boundary The inner green shading 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 472 2009 Macmillan Publishers Limited All rights reserved boundaries define the safe operating space for humanity with respect to the Earth system and are associated with the planet s biophysical subsystems or processes Although Earth s complex systems sometimes respond smoothly to changing pressures it seems that this will prove to be the exception rather than the rule Many subsystems of Earth react in a nonlinear often abrupt way and are particularly sensitive around threshold levels of certain key variables If these thresholds are crossed then important subsystems such as a monsoon system could shift into a new state often with deleterious or potentially even disastrous consequences for humans8 9 Most of these thresholds can be defined by a critical value for one or more control variables such as carbon dioxide concentration Not all processes or subsystems on Earth have well defined thresholds although human actions that undermine the resilience of such processes or subsystems for example land and water degradation can increase the risk that thresholds will also be crossed in other processes such as the climate system We have tried to identify the Earth system processes and associated thresholds which if crossed could generate unacceptable environmental change We have found nine such processes for which we believe it is necessary to define planetary boundaries climate change rate of biodiversity loss terrestrial and marine interference with the nitrogen and phosphorus cycles stratospheric ozone depletion ocean acidification global freshwater use change in land use chemical pollution and atmospheric aerosol loading see Fig 1 and Table In general planetary boundaries are values for control variables that are either at a safe distance from thresholds for processes with evidence of threshold behaviour or at dangerous levels for processes without FEATURE NATURE Vol 461 24 September 2009 evidence of thresholds Determining a safe distance involves normative judgements of how societies choose to deal with risk and uncertainty We have taken a conservative risk averse approach to quantifying our planetary boundaries taking into account the large uncertainties that surround the true position of many thresholds A detailed description of the boundaries and the analyses behind them is given in ref 10 Humanity may soon be approaching the boundaries for global freshwater use change in land use ocean acidification and interference with the global phosphorous cycle see Fig 1 Our analysis suggests that three of the Earth system processes climate change rate of biodiversity loss and interference with the nitrogen cycle have already transgressed their boundaries For the latter two of these the control variables are the rate of species loss and the rate at which N2 is removed from the atmosphere and converted to reactive nitrogen for human use respectively These are rates of change that cannot continue without significantly eroding the resilience of major components of Earth system functioning Here we describe these three processes Climate change Anthropogenic climate change is now beyond dispute and in the run up to the climate negotiations in Copenhagen this December the international discussions on targets for climate mitigation have intensified There is a growing convergence towards a 2 C guardrail approach that is containing the rise in global mean temperature to no more than 2 C above the pre industrial level Our proposed climate boundary is based on two critical thresholds that separate qualitatively different climate system states It has two parameters atmospheric concentration of carbon dioxide and radiative forcing the rate of energy change per unit area of the globe as measured at the top of the atmosphere We propose that human