Synthesis
The concept of planetary boundaries, proposed in 2009, revised in 2015 (Steffen et al.) and again in 2023 (Richardson et al.), aims to define a "safe operating space for humanity" based on the evolution of nine complex, interconnected phenomena: climate change, biodiversity loss, biogeochemical flows (Phosphorus and Nitrogen cycles), land-system change, freshwater use, ocean acidification, stratospheric ozone depletion, atmospheric aerosols loading, introduction of novel entities into the biosphere.
To study the evolution of these phenomena, one or more "control variables" are defined on a global or even regional scale. Acritical "threshold" isset for each of these variables, with an "zone of uncertainty" consisting of two values: a low value ("boundary") and a high value ("limit").The boundary represents the danger zone that precedes the limit beyond which ecosystems could tip over into an unknown state that is probably unfavorable to mankind.
This publication gives an overview of the planetary boundaries approach as proposed in 2015, i.e. before the latest revision in September 20231. It shows how this conceptual framework can be useful on a national or local scale, even if the concept is first and foremost planetary. The fact that most of the planetary boundaries studied have been transgressed underlines the need for ambitious, concerted ecological planning. In this respect, this publication illustrates the main public policies for responding to the issues identified by the notion of planetary boundaries. The main messages drawn from the analysis of the nine planetary boundaries are described below.
1 The latest update of the planetary boundaries framework in September 2023 (Richardson et al.) introduces some new control variables and presents the updated status of each boundary. These changes are summarized in the appendix.
Climate change: a transgressed planetary boundary
In 2023, with an atmosphericcarbon dioxide (CO2) concentration of 425parts per million (ppm), the planet is approaching the planetary limit of 450ppm (high threshold of the uncertainty zone). In 2009, the planetary boundary (low threshold) was already exceeded at 387ppm.
Along with the rest of the world, France's CO2 emissions contribute to the increase in the concentration of greenhouse gases in the atmosphere. Responsible for 2.3% of cumulative historical CO2 emissions into the atmosphere between 1850 and 2021, its average annual per capita CO2 emissions are now similar to the world average, at 4.7 tonnes (t) in 2021. Once imported emissions are taken into account, the averagecarbon footprint (see glossary) of the French (CO2 only) is estimated at 7t in 20212, lower than the Organization for Economic Cooperation and Development (OECD) average, but higher than the global footprint (4.7t).
To keep global warming below+2°C, France's global climate change targets are set out in its national planning tools (energy and climate law, national low-carbon strategy, multi-year energy plan) and, at local level, in regional land-use plans and territorial climate-air-energy plans.
2 When the other two main greenhouse gases, CH4 and N20, are added to CO2 , the average carbon footprint of the French in CO2 equivalent is estimated at 8.9t/capita CO2 eq 2021.
Biodiversity loss: a planetary boundary transgressed
Every year, between 100 and 1,000 extinctions out of a million species are recorded. The planetary boundary of 10 extinctions per year out of amillion species has therefore been exceeded. In France, the extinction risk index is lower than in Europe or the rest of the world, but it is rising faster (+99% between 2000 and 2022, compared with +67% in Europe and +36% in the rest of the world).
The mean abundance of original species, ranging from 0 (ecosystem destroyed) to 1 (undisturbed ecosystem intact), is estimated at 0.36 in France in 2020, below the world average (0.56) and a fortiori the global limit of 0.72.
Numerous tools for protecting species and natural habitats already exist in France. However, the national strategy for protected areas (2022-2030) and the national strategy for biodiversity 2030 aim to step up efforts, in line with the new global framework for biodiversity in 2022, which sets the goal of "living in harmony with nature" by 2050.
Disruption of biogeochemical cycles of nitrogen and phosphorus: a global boundary transgressed for nitrogen
The amount of nitrogen released into the environment by human activities worldwide (150 million tonnes per year - Mt/yr) is well above the thresholds set (62-82Mt/yr). Phosphorus flows from freshwater systems to the ocean worldwide (22Mt) are below the high end of the uncertainty range (100Mt), but above the low end (11Mt). On acontinental scale, the quantities of phosphorus fertilizers applied to soils are above the high value of the uncertainty zone (14.2Mt instead of 11.2Mt).
In France, the surplus of nitrogen (see glossary) supplied to crops by fertilizers is 55 kilograms per hectare (kg/ha) of cultivated agricultural area, on average over the 2010-2019 period. It is above the low threshold of the global limit (41kg/ha) and at the high threshold (55kg/ha), exceeding it in some years. Phosphorus flows discharged into the sea by France remain below the limit: after falling sharply between 2000 and 2020 (-57%), they average 0.23kg/capita/year, well below the low threshold of the limit (1.5kg/capita/year).
Inaccordance with the European "nitrates" directive of 1991, France is implementing nitrate action programs in all of its vulnerable zones in order to provide "the right dose, at the right time and in the right place" and further limit nitrogen leaks. The 2021 Climate and Resilience Act contributes to this target by restricting the use of synthetic fertilizers on land that is not used for agricultural purposes.
Land-system change: global deforestation leading the planet into a zone of uncertainty
With 62% of the world's pre-1700 forest area still forested in 2015, the lower boundary of the uncertainty zone (75% ) has been exceeded, but the global limit (54%) has not. In temperate zones, 50% of the area occupied by pre-1700 forests remains, corresponding to the lower boundary of the uncertainty zone (between 50% and 30%).
While France's forest area is on the increase, our consumption (soy, cocoa, palm oil, etc.) contributes to the deforestation of tropical forests. It isestimated that between 12 and 14.8 million hectares of agricultural and forestry land are mobilized each year outside our borders ("land footprint") to produce goods consumed in France. The associated deforestation ("forest footprint") is estimated at between 26,300 and 64,400 hectares per year. If all humans had a forest footprint identical to that of a French person, the upper threshold of the limit (40% of the original area of tropical and boreal forests destroyed) would be exceeded in around sixty years.
In France, the 2018 national strategy to combat imported deforestation aims to eliminate imports of unsustainable forest or agricultural products contributing to deforestation by 2030. At European level, the regulation on deforestation and forest degradation, adopted in 2023, aims to prohibit the placing on or export from the European market of raw materials and products that have caused deforestation or forest degradation.
Global freshwater use: aplanetary boundary not crossed, but local situations unsustainable
Net withdrawals of freshwater ("blue water") on aglobal scale (2,600 km3) remain below the planetary boundary (4,000 km3). However, there are local overruns (watersheds). According to some researchers, 25% of the world's river basins dry up before reaching the oceans, due to the use of freshwater resources in the basins.
In France, the local limit for blue water is exceeded in some sub-basins during dry summers. Because ofits temperate climate, France contributes 0.2% of the world's annual net freshwater withdrawal (volumes of water withdrawn from the environment that are not directly returned to aquatic environments), a proportion lower than its demographic (0.85%) and economic (2.33%) weight. During the summer months, however, the unsustainability of water withdrawals can be an issue.
In addition to the Schémas directeurs d'aménagement et de gestion des eaux (Sdage - master plans for water development and management), which plan water management at basin level in France, the PTGE (projets de territoire pour la gestion de l'eau - territorial water management projects) aim to adapt needs to available resources as effectively as possible. In order to guarantee water for all, preserve ecosystems and organize sober use, an action plan for resilient and concerted water management was adopted in March 2023, with the aim of reducing abstractions by 10% by 2030.
Ocean acidification: a planetary boundary that hasnot been transgressed, but forhow long?
Since the industrial revolution, the rising levels of CO2 emitted into the atmosphere by human activities have disrupted the biogeochemical balance of the oceans. The ocean is acidifying, threatening ecosystems and marine organisms (shellfish, corals, etc.), particularly in the manufacture of their aragonite calcium skeleton (see glossary). In 2015, aragonite saturation in surface seawater was estimated at 84% of pre-industrial levels, below the planetary boundary of 80% . If we continue at the same pace until 2050, it could reach this level by then.
France is the world's fourth-largest coral reef country, and as such bears a major responsibility for preserving these ecosystems. The national protected areas strategy proposes to include 100% of these coral reefs in a protected area by 2025.
Stratospheric ozone depletion: a planetary boundary not exceeded, thanks to the commitment of the international community
Following the adoption of the Montreal Protocol in 1987 to combat the destruction of the ozone layer, the production and consumption of ozone-depleting substances (chlorofluorocarbons - CFCs - in particular) were sharply reduced. Since the 2000s, the ozone layer has stabilized. Ozone concentration in the stratosphere is estimated at 285 Dobson Units (DU) on average, which means that the global limit (275DU) is respected.
In France, in addition to the ban on certain ozone-depleting substances, the regulations include a set of rules for the certification and monitoring of equipment dependent on fluorinated greenhouse gases. Subsidies have also been set up to support companies wishing to use alternatives to hydrofluorocarbons (HFCs).
Atmospheric aerosol loading: an unquantified planetary boundary
Aerosols are solid or liquid particles suspended in the air, ranging in size from a few nanometers to tens of micrometers. While the majority of aerosols are of natural origin, an increasing quantity has been released into the atmosphere by human activities since the pre-industrial era, representing a major challenge for climate and human health. Given the spatio-temporal variability of these particles and the diversity of their sources and impacts, it has not yet been possible to identify a global threshold. Only a local boundary specific to Southeast Asia has been proposed.
In France, the implementation of strategies and action plans over the last few years has led to a sharp drop in air pollutant emissions. The new national plan for the reduction of atmospheric pollutant emissions (PREPA) adopted in 2022 will enable us to go even further, particularly with regard to fine particles and nitrogen oxides (NOx). PREPA combines regulatory, fiscal and incentive measures, as well as planning tools for local authorities and awareness-raising campaigns.
Introduction of novel entities into the biosphere: a planetary boundary not precisely quantified but considered exceeded
Novel entities refer to all entities, in the geological sense, produced, circulated and released into the environment by human activities. These entities (synthetic substances, new forms of existing substances, modified life forms) can be persistent and move over large geographical areas. The production and release of these entities, as well as the diversity of substances involved, is increasing at such a rate that it is outstripping the capacity of companies to carry out safety assessments and controls, before releasing products that are potentially dangerous for the planet. Today, 350,000 chemical products are sold on the world market, representing a 50-fold increase in production since 1950. Of all these substances, plastic pollution is the focus of particular attention.
In France, provisions to regulate the release of novel entities have been adopted under the precautionary principle enshrined in Article 5 of the Constitutional Charter for the Environment. The 2020 anti-waste law for a circular economy provides for the end of single-use plastic packaging on the market by 2040, as well as targets for reduction, reuse or re-employment, and recycling. At international level, France is strongly behind the proposed international treaty against plastic pollution.