Quantifying land use as one method of anticipating a planetary state shift. The trajectory of the green line represents a fold bifurcation with hysteresis12. At each time point, light green represents the fraction of Earth’s land that probably has dynamics within the limits characteristic of the past 11,000 yr. Dark green indicates the fraction of terrestrial ecosystems that have unarguably undergone drastic state changes; these are minimum values because they count only agricultural and urban lands. The percentages of such transformed lands in 2011 come from refs 1, 34, 35, and when divided by 7,000,000,000 (the present global human population) yield a value of approximately 2.27 acres (0.92 ha) of transformed land for each person. That value was used to estimate the amount of transformed land that probably existed in the years 1800, 1900 and 1950, and which would exist in 2025 and 2045 assuming conservative population growth and that resource use does not become any more efficient. Population estimates are from refs 31–33. An estimate of 0.68 transformed acres (0.28 ha) per capita (approximately that for India today) was used for the year 1700, assuming a lesser effect on the global landscape before the industrial revolution. Question marks emphasize that at present we still do not know how much land would have to be directly transformed by humans before a planetary state shift was imminent, but landscape-scale studies and theory suggest that the critical threshold may lie between 50 and 90% (although it could be even lower owing to synergies between emergent global forcings). See the main text for further explanation. Billion, 109.
"Approaching a state shift in Earth’s biosphere"; https://www.nature.com/articles/nature11018
Drivers of a potential planetary-scale critical transition. a, Humans locally transform and fragment landscapes. b, Adjacent areas still harbouring natural landscapes undergo indirect changes. c, Anthropogenic local state shifts accumulate to transform a high percentage of Earth’s surface drastically; brown colouring indicates the approximately 40% of terrestrial ecosystems that have now been transformed to agricultural landscapes, as explained in ref. 34. d, Global-scale forcings emerge from accumulated local human impacts, for example dead zones in the oceans from run-off of agricultural pollutants. e, Changes in atmospheric and ocean chemistry from the release of greenhouse gases as fossil fuels are burned. f–h, Global-scale forcings emerge to cause ecological changes even in areas that are far from human population concentrations. f, Beetle-killed conifer forests (brown trees) triggered by seasonal changes in temperature observed over the past five decades. g, Reservoirs of biodiversity, such as tropical rainforests, are projected to lose many species as global climate change causes local changes in temperature and precipitation, exacerbating other threats already causing abnormally high extinction rates. In the case of amphibians, this threat is the human-facilitated spread of chytrid fungus. h, Glaciers on Mount Kilimanjaro, which remained large throughout the past 11,000 yr, are now melting quickly, a global trend that in many parts of the world threatens the water supplies of major population centres. As increasing human populations directly transform more and more of Earth’s surface, such changes driven by emergent global-scale forcings increase drastically, in turn causing state shifts in ecosystems that are not directly used by people. Photo credits: E.A.H. and A.D.B. (a–c, e–h); NASA (d).
The Earth’s climate system is highly nonlinear
The above is again getting the attention it deserves...
Significance: we have no idea what we are in the process to trigger, as our current models can't simulate non-linearity...
In the comments some studies on the matter
#climate #uöäü1non-linear