The concept of planetary boundaries designates the limits not to be exceeded if mankind is able to develop in a safe ecosystem, that is to say avoiding brutal and difficult to predict environmental changes.
An international team of 26 researchers explained this concept in 2009, identifying nine planetary boundaries and considering that the thresholds were exceeded for three of the seven limits for which they proposed limit values. An update published in 2015 adds a tenth limit and reports a fourth-limit.
Initial definition 2009
(Planetary limits according to the report Rockström et al. Published in Nature in 2009. Red areas represent the current state estimated and the green circle defines the estimated limits, https://commons.wikimedia.org/wiki/File:Planetary_Boundaries.png)
In 2009, an international team of 26 researchers, led by Johan Rockström of the Stockholm Resilience Centre and Will Steffen of the Australian National University, published an article in Nature in which it identified nine planetary boundaries to not be exceeded if humanity wants to develop in a safe ecosystem, that is to say, avoiding abrupt , nonlinear, difficult to predict and potentially catastrophic changes for the environment. Among these researchers, it may be noted among other climatologist James Hansen (Director of the Goddard Institute for Space Studies at NASA, a pioneer in research on climate change), Paul Crutzen (Nobel Prize in Chemistry 1995), the German climatologist Hans Joachim Schellnhuber (founder of the Potsdam-Institut für Klimafolgenforschung and advisor to the German government and the European Commission on global warming) and the Belgian geographer Eric Lambin.
The authors then considered that the thresholds were exceeded for three of the seven limits for which they propose limits in terms of volume emitted or extracted from the environment:
climate change: atmospheric CO2 concentration < 350 ppm and/or a maximum variation of +1 W/m² of radiative forcing.
erosion of biodiversity: extinguishing “normal” rate of species < 10 species per year for over a million. However, the current global extinction rate is 10-100 times higher. These disappearances have major impacts on ecosystems and the functions that are no longer met by the extinct species.
disturbance of the biochemical cycles of nitrogen and phosphorus: limited to industrial and agricultural N2 fixation of 35 TgN/year and yearly contribution of phosphorus to oceans < 10 times the natural leaching of phosphorus. The modification of the nitrogen and phosphorus cycles in soils resulting in particular from agricultural and intensive livestock farming. The use of fertilizers and manure from livestock contribute to disrupting these vital cycles of good soil and water. The limit was already reached in 2009 for nitrogen.
Four planetary boundaries had not yet been crossed:
- changes in land use: up to 15% of the surface of ice-free land converted to cropland.
- freshwater use: < 4,000 km³/year consumption of runoff water resources,
- decrease in stratospheric ozone layer: reduction of < 5% in the ozone concentration compared to pre-industrial level of 290 Dobson units,
- ocean acidification: average rate of saturation of the water surface sea aragonite ≥ 80% of the pre-industrial level.
Two limits could not yet be quantified due to lack of data:
- chemical pollution (radioactive compounds, heavy metals, synthetic organic compounds)
- concentration of atmospheric aerosols.
The authors emphasized the interactions between these limits. The concept of planetary boundaries to define the planetary playing field in which humanity could live in safety.
Consideration by the United Nations
The Secretary-General of the United Nations, Ban Ki-moon, entered the concept of planetary boundaries on March 16, 2012, when he presented the key points of the report of the “High-level Panel on Global Sustainability” at an informal plenary session of the General Assembly of the United Nations. He said: “The vision of the High Level Group is to eradicate poverty and reduce inequality, make growth inclusive, and production and consumption more sustainable, while combating climate change and respecting a series of other planetary boundaries “. The concept was incorporated in the initial version of the conclusions of the United Nations Conference on Sustainable Development to convene in Rio de Janeiro on June 20-22, 2012, but the use of the concept was then removed from the Conference text, partly because of fears of some poor countries that its adoption could lead to the setting aside of poverty reduction and economic development. It is also, according to observers, “because the idea is just too new to be formally adopted, and needed to be submitted to the dispute, matured and ruminated to test its strength before having a chance be internationally accepted in UN negotiations.”
In January 2015, these scientists published in Science a refresh of their work, which concludes that the four planetary boundaries are now obsolete or about to be:
- climate change: the international scientific community admits that, to limit the extent of global warming to 2 °C by 2100 (compared to 1990), the atmospheric CO2 concentration should not exceed a limit of between 350 and 450 ppm (parts per million). However, the current concentration reaches 400 ppm recently, and 450 ppm could be exceeded if the current growth of greenhouse gas emissions continues.
- erosion of biodiversity: limit already exceeded in 2009.
- disturbance of the nitrogen cycle: the limit was already reached in 2009.
- disruption of the phosphorus cycle: the limit is now also crossed for phosphorus, but with significant regional variations.
The analysis of land uses changes limit has been refocused on the natural climate regulation process through exchanges of energy, water and CO2 between the soil and the atmosphere. The researchers are particularly interested in the role of forests in regulating this and find that to continue enjoying their profits, it would increase their acreage, including tropical and boreal forests.
Three other planetary boundaries have not yet been crossed:
- use of fresh water,
- decrease in the stratospheric ozone layer,
- ocean acidification.
The tenth limit concerning the diffusion of “new entities” in the environment (synthetic molecules, nanoparticles, …), which may have biological and/or geophysical harmful consequences. More than 100,000 substances in this category are now marketed worldwide, but their environmental impact is largely unknown and is probably very complex. Researchers believe therefore unable to set a global limit for these substances, but invite to better monitor and limit their use as much as possible.
The authors focus on the systemic dimension of the impacts caused by exceeding the planetary boundaries. They insist particularly on the risks of climate change and biodiversity loss, two fundamental limitations that could, if exceeded substantially and persistently, “cause the Earth system to a new state”, potentially destructive for planet and its inhabitants. They also remind that the interaction of these limits should not be underestimated, as the inertia of natural systems: for example, even if global emissions of greenhouse gases tomorrow interrupted, concentration of these gases already emitted into the atmosphere could be enough to permanently disrupt the climate.
Translated from Wikipedia