Overshooting and exceeded planetary boundaries guarantees societal collapse, global conflict, and extinction

Overshooting the Earth System thus means that the supply sources, activity spaces and disposal sites are overused (Catton, 1982, 1998). According to Rees (2021) overshoot is “a meta-problem, the cause of most so-called ‘environmental problems’ including climate change [...]. Climate change is therefore only a symptom of overshoot, implying that only reducing carbon emissions, the cause of anthropogenic global warming, will not solve all environmental problems.” The neo-Malthusian problem has become one, not of scarcity of some particular resource, food, or of too much carbon emissions, but of the entire human “ecological footprint” which is too large, and causes an overshoot. The term ecological footprint was introduced by Wackernagel and Rees (1996). Hoekstra and Wiedmann (2014, p.1114) describe an ecological footprint as an indicator “of human pressure on the environment and form the basis for understanding environmental changes that result from this pressure (such as land-use changes, land degradation, reduced river flows, water pollution, climate change) and resultant impacts (such as biodiversity loss or effects on human health or economy).” They distinguish seven types of ecological or environmental footprints: land, energy, water, materials, carbon, nitrogen, and biodiversity footprints - and state that the carrying capacity of the Earth system in terms of carbon, energy, land, material, and water has been exceeded (Hoekstra and Wiedmann, 2014). Measuring the carrying capacity of Earth systems and determining whether a particular environmental footprint is exceeding this, which would signal overshoot, has resulted in the development of the concept of “planetary boundaries” (Rockstr¨om et al., 2009). Nine planetary boundaries have been identified. These are climate change, ocean acidification, ozone depletion, nitrogen and phosphorus cycles, global freshwater use, land systems change, rate of biodiversity loss, atmospheric aerosol loading and chemical pollution (Rockstr¨om et al., 2009; Steffen et al., 2015). Rockstr¨om et al. (2009) estimated that at least three of the planetary boundaries have been exceeded: “for climate change, rate of biodiversity loss, and changes to the global nitrogen cycle” (Rockstr¨om et al., 2009, p.1). While in itself problematic, the bigger danger is that the breach of only a few planetary boundaries can potentially lead to the entire Earth system tipping, resulting in “abrupt global environmental change.” This is due to the interdependence between the various planetary boundaries and non-linear feedback effects between them, which implies that there could be potential climate tipping points, 11 or thresholds, which if exceeded, may cause the tipping of the Earth system into a state which would be detrimental to civilization and life (Rockstr¨om et al., 2009; Lenton et al., 2019; Ritchie et al., 2021). It threatens societal collapse, and even poses an existential risk (Richards et al., 2021). “The prospect of civilization collapse has now entered the mainstream of scientific and popular discourse” (Gowdy, 2020, p.2). Climate change, which through a cascade of breached tipping points could cause a megahothouse, is considered an existential threat for several reasons (Kemp et al., 2022). One is that global warming directly threatens agriculture and food supply. According to Gowdy (2020, p.2) “Climate models indicate that the Earth could warm by 3°C-4 °C by the year 2100 and eventually by as much as 8 °C or more. This would return the planet to the unstable climate conditions of the Pleistocene when agriculture was impossible.” He refers here to the fact that climates have been comparatively stable over the past 12,000 years (the Holocene) which allowed human societies to switch from hunting and gathering to large scale farming. A second reason why breaching planetary boundaries could pose an existential threat is that environmental change is implicated in all past mass extinction events (Kemp et al., 2022). Song et al. (2021, p.1) points out that mass species extinction12 in the past have been associated with tipping points in climate change of >5.2 degrees Celsius magnitudes. Bradshaw et al. (2021) and Dirzo et al. (2022) consider the current rate of biodiversity loss to be so significant that it signifies that humans have triggered the planet’s sixth mass extinction. A growing number of authors and scientists indeed warn that a sixth mass extinction may be beginning or imminent - e.g. Barnosky et al. (2011), Cowie et al. (2022), Kaiho (2022), Kolbert (2014) and McCallum (2015). Other reasons that have been cited for the breaching of planetary boundaries as existential threat, is that environmental collapse, say due to climate change, or water scarcity, or biodiversity loss, could cause global conflict, could increase vulnerability to other shocks, cause systemic crises, and reduce humanity’s ability to recover from other catastrophes (Kemp et al., 2022). Thus, economic growth has lead humanity to overshoot the capacity of the Earth system, and this poses an existential risk. This is why Rees (2021) has described overshoot as “ultimately a fatal condition.”The existential risk is increasing given that the extent of overshooting is increasing13 and shows no sign of diminishing, as measured for instance by the Material Footprint (MF) / Raw Material Consumption (RMC) indicator (Fanning et al., 2022; Giljum et al., 2015; Wiedmann et al., 2015).