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Climate change

A transgressed planetary boundary

To understand the mechanisms, causes and effects of climate change, we need to look at a natural phenomenon known as the greenhouse effect. Certain gases, such as carbon dioxide and methane, naturally present in the atmosphere, absorb part of the infrared heat radiation emitted by the Earth's surface towards space, to counterbalance the solar energy absorbed. These gases, known as "greenhouse gases" (GHGs), help maintain the Earth's surface temperature at 15°C. Without this natural greenhouse effect, the average temperature would be around-18°C, making the planet an inhospitable place to live.

Since the industrial revolution, this phenomenon has been disrupted by the appearance of an "additional greenhouse effect" induced by growing human influence, which is almost entirely responsible for climate change. The main greenhouse gases emitted into the atmosphere by human activities are carbon dioxide (CO₂), which comes from the extraction and use of fossil fuels (transport, industry, heating) and the implementation of industrial processes (cement production, etc.); methane (CH₄), which comes from the burning of fossil fuels (oil, gas, coal, etc.); anthropogenic methane (CH₄) (see glossary), mainly from enteric fermentation by ruminants, rice cultivation and waste processing; nitrous oxide (N₂O), mainly due to the use of fertilizers and certain industrial processes.

As part of the work on planetary boundaries, researchers have defined two control variables for understanding the evolution of climate change: the concentration ofCO₂ in the atmosphere (in parts per million) and the energy imbalance at top-of-atmosphere compared with the pre-industrial era (in watts per square metre) - (Table 2). "Radiative forcing" refers to an imbalance in the Earth's radiation balance (see glossary) induced by the increased concentration of GHGs in the atmosphere, preventing part of the infrared radiation from escaping into space. This imbalance is the process that leads to atmospheric warming.

Table 2: Control variables and planetary boundary for climate change

Control variables	Thresholds and areas of uncertainty	Global values
Atmospheric CO₂ concentration in parts per million (ppm)	350 ppm CO₂ (350-450 ppm)	425 ppm in April 2023 379 ppm in2005⁸
Energy imbalance at top-of-atmosphere in watts per square metre (W/m²) compared with the pre-industrial era	+ 1.0W/m² (+ 1.0 - + 1.5W/m²)	+ 2.72W/m² in 2019 + 1.66W/m² in 2005

Source: based on Steffen et al., 2015

8 IPCC, 2007. Climate change 2007: the scientific evidence.

The values presented above show that the planetary boundary for Energy imbalance at top-of-atmosphere has been exceeded, and that the CO₂ concentration in the atmosphere, which has been rising steadily since the pre-industrial era (280 ppm), has reached a limit. In 2009, the low end of the uncertainty zone was already exceeded at 387 ppm. By 2023⁹, at 425 ppm, the planet will be approaching the high threshold. If such a rise continues, many regions could become more unstable and vulnerable, with serious repercussions on living conditions and ecosystems.

9 US national agency Earth Systems Research Laboratories (ESRL) - Surveys carried out at the Mauna Loa site (Hawaii, USA).

Consequences and challenges

According to the first volume of the latest report by the Intergovernmental Panel on Climate Change (IPCC, 2021¹⁰ ), "recent climate changes are widespread, rapid and intensifying. They are unprecedented in thousands of years". Every year, 25 million people are confronted with more numerous and more intense natural disasters, forced to flee their countries in order to survive¹¹. Sub-Saharan Africa and South-East Asia are the regions currently most affected. The impacts of climate change are manifold:

increase in global surface temperature: about 1.1°C compared with 1850-1900;
Sea level rise: 15 cm to 20 cm since the beginning of the 20^th century ;
decrease in the surface of the Arctic ice pack in September: -40% since 1979;
melting glaciers: unprecedented for at least 2000 years ;
an increase in extreme climatic events: heat waves, precipitation, drought; weather conditions conducive to fires, ocean acidification.

10 IPCC, August 2021. 6^th ClimateReport - Working Group 1.
11 World Bank, 2021. Groundswell Report. Taking action on internal climate migration.

According to its projections, the IPCC points out that declining agricultural yields in some regions could lead to a shortage of food sources, affecting the health of populations. More frequent and intense extreme weather events could lead to the displacement of 216 million migrants by 2050 (World Bank). Melting glaciers will have serious consequences for oceans, ocean currents and climate. Rising sea levels will have repercussions on certain rivers, increasing the risk of flooding or submersion at their mouths. These events will also have serious consequences for biodiversity and ecosystems.

France's contribution to transgressing the planetary boundary

Between 1850 and 2021, France emitted 2.3% of cumulative global CO₂ emissions (excluding emissions linked to land-use change). The proportion is small, but it nonetheless identifies France's historical responsibility for the accumulation of CO₂ in the atmosphere, the cause of current global warming (Figure 2).

Over 75% of cumulative global CO₂ emissions come from the USA (25%), the European Union (EU) - (17%), China (15%), Russia (7%), the UK (4%), Japan (4%), India (3%) and Canada (2%). However, for the past two decades, CO₂ emissions have been falling in the USA and Europe, while rising in the rest of the world, particularly Asia. Between 2000 and 2021, annual CO₂ emissions fell by an average of 1.2% in Europe and 0.9% in the USA, compared with an average annual growth rate of 5.6% in China.

Figure 2: Historical cumulative CO₂ emissions by continent and in France

Scope: CO₂ from fossil fuels and cement, excluding land use, land-use change and forestry; excluding international bunkers.
Source: Global Carbon Project. Processing: SDES, February 2023

Where does France stand in terms of contemporary emissions?

Now that the planetary boundary has been crossed, global CO₂ emissions, less those absorbed by artificial carbon sinks, should be zero, so as not to add any additional CO₂ molecules to the atmosphere. This situation, where emissions are offset by absorptions, characterizes the concept of "carbon neutrality" (see glossary). If carbon neutrality were achieved, the atmospheric concentration of GHGs would gradually fall to below threshold levels.

Two approaches can be used to estimate France's GHG emissions:

The national inventory records the quantities of GHGs physically emitted within the country (territorial approach). It is the official data set used for international and national climate policies.
The carbon footprint is an estimate of the GHGs induced by a country's domestic final demand (final consumption and investments). The footprint is made up of national emissions (excluding emissions linked to exports) and emissions associated with imports of goods and services consumed by the French.

In 2021, excluding land use, land-system change and forestry, France's CO₂ emissions presented in the national inventory represent 0.82% of global emissions. According to the carbon footprint approach, taking into account imported emissions, this proportion rises to 1.27%. France's annual contribution to the greenhouse effect should be seen in the context of its demographic (0.85%) and economic (2.33%) weight in the world.

In the inventory, average annual CO₂ emissions (excluding other greenhouse gases) per inhabitant of France are similar to those of the world average (4.7 t in 2021). Thus, for 2021, on average, the French have contributed as much as the rest of the world's inhabitants to keeping emissions above the planetary boundary. From this point of view, the efforts required to reduce emissions below the thresholds are the same in France as in the rest of the world, on average.

The carbon footprint approach accentuates France's relative climate pressure. The average annual carbon footprint of the French ( CO₂ only) is estimated at 7.0 tonnes in 2021¹². The French CO₂ footprint exceeds the world average by 48%.

12 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 8.9 t/capita CO₂ eq 2021.

Climate policies and actions

Since the adoption of the United Nations Framework Convention on Climate Change in 1992, global coordination to combat climate change has been established. In particular, the Paris Agreement, concluded in 2015 at the Paris Climate Change Conference, sets a target of limiting global warming to well below 2°C compared with the pre-industrial era, and of continuing efforts not to exceed 1.5°C. The signatory countries undertake to contribute to this global objective by defining national emission reduction efforts, which must show a progression over time.

At European level, as part of the Green Pact published at the end of 2019, a "climate package", i.e. a set of legislation to combat climate change, has been proposed for 2021. The aim of this package, also known as"Fit for 55", is to reduce GHG emissions by at least 55% by 2030, to achieve carbon neutrality by 2050. Within this framework, two important measures were adopted at the end of 2022: the goal of zero-emission road mobility by 2035, and the implementation of a border carbon adjustment mechanism, often referred to as a " border carbon tax", to prevent carbon leakage. This latter mechanism will require importers of products manufactured outside Europe to acquire carbon certificates corresponding to the price of carbon that would have been paid if the product had been manufactured in the EU.

The European GHG Emissions Trading Scheme, also known as the "carbon market", launched in 2005, is one of the main tools for reducing GHG emissions. The quantity of emission allowances is determined by public authorities, then distributed to covered installations, which can resell them or buy new ones on a market. These installations must then return the same quantity of emission allowances to the public authority as they actually emitted. Today, this market covers almost 45% of the EU's GHG emissions (11,000 installations in the power generation, heating networks, steel, cement, refining, glass, paper and, since 2012, aviation sectors). The Fit for 55 package plans to extend the scheme to new sectors, and to complement it with a border carbon adjustment mechanism to cover the GHG emissions of products imported into the EU.

These international targets are set out in French planning tools (the French Energy and Climate Act, the national low-carbon strategy, the multi-year energy plan).

At regional level, climate change objectives are set out in regional plans for sustainable development and territorial equality (SRADDET) (see glossary), regional climate-air-energy plans (SRCAE) and, at inter-municipal level, territorial climate-air-energy plans (PCAET). In French overseas departments, the corresponding planning document is the regional development plan (SAR).

Strategies, schemes and plans concern all sectors of activity. Their purpose is to mobilize economic, social and environmental players and launch actions, notably to accelerate the energy renovation of buildings, promote the changeover of heating systems to more efficient systems, act on public lighting, promote more sober mobility (carpooling, soft mobility, modal transfers, telecommuting, combating urban sprawl, etc.), improve territorial logistics systems (short circuits, etc.), and help develop renewable energies.

Private players can also get involved in the fight against climate change, notably through the low-carbon label, created in 2019. This label certifies greenhouse gas reduction or carbon sequestration projects¹³. These certified projects can then be financed on a voluntary basis by private or public organizations, for example to offset their residual emissions.

13 By mid-2022, 168 projects have been awarded the low-carbon label, representing over 450,000 potential tons of CO₂ (260,000 for funded projects), with a target of 1 million tons of CO₂ . These projects include forestry projects (reforestation, afforestation on non-forest land, conversion of mature coppice into mature forest) and agricultural projects (increasing soil carbon storage, sustainable hedge management, orchard planting).

Where does France stand in meeting its international political objectives?

With the aim of achieving carbon neutrality by 2050, France's climate policy, set out in the national low-carbon strategy, is aligned with the global emissions trajectory that will limit the increase in average global temperature to + 1. 5°C by the end of the century, and respect the global limit ( CO₂ concentration) by the end of the century.

The 6^th Assessment Report on Climate Science, produced by the IPCC, presents the results of climate modelling. Taking into account the quantity of CO₂ already emitted into the atmosphere, the scientists estimate the emissions that human activities can still emit while limiting the rise in temperature to + 1. 5°C or + 2°C, by 2100 compared with the pre-industrial era. This "carbon budget" (see glossary) amounts respectively to 400 gigatonnes (Gt) for + 1. 5°C and 1,150 Gt of CO₂ for + 2°C (67% confidence in the estimate).

Assuming a strictly egalitarian distribution of the carbon budget remaining to be emitted by all the planet's inhabitants, each human being, and any unborn descendants, will have a range of between 51 t (+ 1. 5°C) and 148 t of CO₂ (+ 2°C) for the rest of his or her life (Figure 3). For the year 2021 alone, the average annual emissions of the French are 4.7 t of CO₂ per person and 7.0 t of CO₂ in the footprint approach (Figure 4). This assumption of a strictly egalitarian distribution of carbon budgets does not include possible intra-generational or geographical distributions that would take into account the age of populations or the historical responsibilities of each country.

Figure 3: Total CO₂ budget allocated to each human being in 2021, compatible with the Paris Agreement

Figure 4: Average annual CO₂ emissions and footprint of the French in 2021

Note: the IPCC carbon budget corresponds to the total CO₂ emissions that still need to be emitted to limit warming to + 1.5°C and + 2°C, distributed equitably among all human beings in 2021.
Scope: CO₂ emissions only, excluding land use, land-use change and forestry.
Sources: Citepa; SDES; IPCC, AR6 WG August 2021. Processing : SDES, February 2023

Scientists have defined trajectories for the consumption of these carbon budgets between 2021 and 2100. To limit global warming to + 1.5°C by 2100, we need to be carbon neutral by 2050, and by 2075 to limit global warming to + 2°C. Carbon neutrality defines a zero balance between emissions and storage by land, forests or technology.

Taking into account average forecasts for world population growth and projected emissions reductions to limit global warming, it is possible to estimate what average annual emissions should be up to 2100. By 2030, with a view to limiting global warming to+2°C, average territorial emissions should fall by around 42%, and the carbon footprint should be almost halved. By 2050, the average carbon footprint of a French person would have to decrease by a factor of 4 to 5 to limit warming to +2°C (Figure 5). Figure 5 shows GHG footprints, whereas the emissions data presented previously (Figures 3 and 4) relate solely to CO₂ (which represents 75% of all GHGs).

Figure 5: Average annual GHG footprint* of the French in 2021 and estimated targets for average annual emissions** per person worldwide in 2030 and 2050

* GHG footprint : CO₂ , CH₄ , N₂O .
** Estimated emissions targets : all GHGs.
Scope: CO₂ , CH₄ , N₂O emissions for the French footprint in 2021, and all GHGs for estimated emissions targets worldwide in 2030 and 2050.
Sources: Citepa; SDES; IPCC, AR6 WG3; UN. Processing: SDES, February 2023

Further information

MTECT, Combating climate change.
MTECT, Resource center for adaptation to climate change.
MTECT, Carbon markets.
MTECT, Climate action by companies and local authorities.
Steffen, W. et al., 2015. Planetary Boundaries: Guiding Human Development on a Changing Planet. Science 347 (6223): 1259855-55.

TO ACT

Ademe, Guide PCAET - Comprendre, construire et mettre en œuvre.
Cerema, La boussole de la résilience - Repères pour la résilience territoriale.
France Relance, Transition agricole, alimentation et forêt section.
France'Renov, to renovate your home.

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