Tripping over tipping points/elements

Abstract

The term ‘‘tipping point’’ has been used to identify a critical threshold susceptible to a tiny perturbation that can qualitatively alter the state or development of a system. ‘‘Tipping element’’ has been introduced to describe largescale components of the Earth system that may pass a tipping point. A special issue of the Proceedings of the National Academy of Science of the United States (PNAS) recently focused on Tipping Elements in Earth Systems has examined potential policy-relevant tipping elements in the climate system with anthropogenic forcing. Subjects such as the evaluation of El Nino/southern oscillation response to global warming, irreversible ice sheet retreat and unstoppable loss, and climate change induced Amazon rainforest dieback were presented in this special issue. An earlier PNAS research article investigated the imprecision of probability assessments of tipping points identified for the global climate system. The United Nations Environment Program (UNEP) has underscored the importance of land degradation by human activity and the condition of the planet’s assessed ecosystems as instances of critical thresholds and tipping points important to the global environment and governments. The UNEP calls global government to establish more environmentally sustainable business practices in response to the concern for these approaching thresholds and tipping points. Proc Nat Acad Sci 2009, 106(49), 20561–20621; 105(6), 1786–1793; 2008, 106(13), 5041–5046; http://www.unep. org/geo/yearbook/yb2009. Next generation biofuel environmental and sustainability factors