This planetary boundaries framework update finds that six of the nine boundaries are transgressed, suggesting that Earth is now well outside of the safe operating space for humanity. Ocean acidification is close to being breached, while aerosol loading regionally exceeds the boundary. Stratospheric ozone levels have slightly re- covered. The transgression level has increased for all boundaries earlier identified as overstepped. As primary production drives Earth system biosphere functions, human appropriation of net primary production is pro- posed as a control variable for functional biosphere integrity. This boundary is also transgressed. Earth system modeling of different levels of the transgression of the climate and land system change boundaries il- lustrates that these anthropogenic impacts on Earth system must be considered in a systemic context.

The planetary boundaries framework (1, 2) draws upon Earth system science (3). It identifies nine processes that are critical for maintaining the stability and resilience of Earth system as a whole. All are presently heavily perturbed by human activities. The framework aims to delineate and quantify levels of anthropo- genic perturbation that, if respected, would allow Earth to remain in a “Holocene-like” interglacial state. In such a state, global environ- mental functions and life-support systems remain similar to those experienced over the past ~10,000 years rather than changing into a state without analog in human history. This Holocene period, which began with the end of the last ice age and during which agriculture and modern civilizations evolved, was characterized by relatively stable and warm planetary conditions. Human activities have now brought Earth outside of the Holocene’s window of environmental variability, giving rise to the proposed Anthropocene epoch (4, 5).

Planetary-scale environmental forcing by humans continues and individual Earth system components are, to an increasing extent, in disequilibrium in relation to the changing conditions. As a conse- quence, the post-Holocene Earth is still evolving, and ultimate

lobal environmental conditions remain uncertain. Paleoclimate re- search, however, documents that Earth has previously experienced largely ice-free conditions during warm periods (6, 7) with corre- spondingly different states of the biosphere. It is clearly in human- ity’s interest to avoid perturbing Earth system to a degree that risks changing global environmental conditions so markedly. Ice cover is only one indicator of substantial system-wide change in numerous other Earth system dimensions. The planetary boundaries frame- work delineates the biophysical and biochemical systems and processes known to regulate the state of the planet within ranges that are historically known and scientifically likely to maintain Earth system stability and life-support systems conducive to the human welfare and societal development experienced during the Holocene.