Planetary boundaries and palaeoecology
The need for information on long-term change throughout the Holocene provides an interface for sustainability science and palaeoecology.
The concepts of “planetary boundaries” represent a set of nine critical thresholds in Earth’s biophysical systems, including climate change, biodiversity loss, and land-system change (Rockström al., 2019). For each boundary, a “safe operating space” is delineated indicating the range of variability that can occur without significantly disrupting the critical planetary systems. We have already transgressed most boundaries, and risk the breakdown of biophysical processes. Leading thinkers in the field have suggested that we are currently at a fork in the road, presented with the choice between our continued trajectory towards hothouse earth, or a return to more stable conditions more typical of the Holocene - the warm period that began about 12 thousand years ago.
As the world continues on its unsustainable trajectory towards “hothouse earth”, it is essential to define a safe operating space for key biological and environmental processes. Charting pathways that could stabilise earth system processes requires knowledge of how Earth systems have varied throughout the Holocene, and whether and how far we have deviated from past ranges of variability. Such information can inform decisions about where change could be resisted, accepted, or where adaptation is inevitable.
The Holocene (past 12000 years) provides important reference conditions as it is during this period of relative stability that human societies have thrived and innovated. The need for information on long-term change throughout the Holocene provides an interface for sustainability science and palaeoecology - the study of past biological and environmental interactions. Palaeoecology uses environmental archives such as fossil pollen, isotopes, and spores, often from lake sediments, to reconstruct past environmental change.
Figure 1: Conceptual diagram showing how knowledge of variability throughout the Holocene could help inform safe operating spaces. The dark-green area shows the Holocene range of variability and the grey sphere shows present and future positions of the system, and dotted lines represent alternative trajectories. The safe operating space expands in the Anthropocene (shown in paler green) as we accept that Holocene conditions may no longer be feasible, in which case adaptation to novel conditions will be needed (after Dearing et al. 2014).
In a recent paper in Global Change Biology, Gillson and colleagues address the need for high-quality data covering a range of spatial and temporal scales, that will be key in delineating safe operating spaces. The authors propose integrating insights on how ecosystems responded to past environmental changes to refine the planetary boundaries framework. Paleoecology reveals how Earth’s systems responded to key changes in anthropogenic influence, including the spread of pastoralism and agriculture, colonisation and industrialisation, as well as past warn periods within the Holocene. Palaeoecological studies can identify the thresholds where earth systems reorganise, information which can help identify when we are approaching tipping points which could be resisted or will require adaptation. Currently, data is not available at global scales for all of the planetary boundaries, and the paper explores how information from selected areas might contribute to scaling up to planetary scales.
An accompanying perspective highlights how paleoecology provides a potentially powerful tool for strengthening planetary boundary research, offering a long-term perspective on Earth’s systems and their responses to change, helping to guide us to a more sustainable future.