Trajectories of the Earth System in the Anthropocene
- aStockholm Resilience Centre, Stockholm University, 10691 Stockholm, Sweden;
- bFenner School of Environment and Society, The Australian National University, Canberra, ACT 2601, Australia;
- cCenter for Macroecology, Evolution, and Climate, University of Copenhagen, Natural History Museum of Denmark, 2100 Copenhagen, Denmark;
- dEarth System Science Group, College of Life and Environmental Sciences, University of Exeter, EX4 4QE Exeter, United Kingdom;
- eThe Beijer Institute of Ecological Economics, The Royal Swedish Academy of Science, SE-10405 Stockholm, Sweden;
- fSchool of Geography and Development, The University of Arizona, Tucson, AZ 85721;
- gScott Polar Research Institute, Cambridge University, CB2 1ER Cambridge, United Kingdom;
- hJasper Ridge Biological Preserve, Stanford University, Stanford, CA 94305;
- iEarth and Life Institute, Université catholique de Louvain, 1348 Louvain-la-Neuve, Belgium;
- jBelgian National Fund of Scientific Research, 1000 Brussels, Belgium;
- kResearch Domain Earth System Analysis, Potsdam Institute for Climate Impact Research, 14473 Potsdam, Germany;
- lDepartment of Environmental Sciences, Wageningen University & Research, 6700AA Wageningen, The Netherlands;
- mDepartment of Physics and Astronomy, University of Potsdam, 14469 Potsdam, Germany
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Edited by William C. Clark, Harvard University, Cambridge, MA, and approved July 6, 2018 (received for review June 19, 2018)

Abstract
We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a “Hothouse Earth” pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System—biosphere, climate, and societies—and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values.
Footnotes
- ↵1To whom correspondence may be addressed. Email: will.steffen{at}anu.edu.au or john{at}pik-potsdam.de.
Author contributions: W.S., J.R., K.R., T.M.L., C.F., D.L., C.P.S., A.D.B., S.E.C., M.C., J.F.D., I.F., S.J.L., M.S., R.W., and H.J.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1810141115/-/DCSupplemental.
- Copyright © 2018 the Author(s). Published by PNAS.
This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).
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