Understanding the impact of greenhouse gas emissions on the climate
On June 20, 2024, the Haut Conseil pour le Climat (HCC) published its annual report. The HCC is an independent body responsible for evaluating public action in favor of the climate in France. In its latest report, it hails the fall in greenhouse gas (GHG) emissions in France: indeed, it records a 5.8% drop in GHG emissions in 2023 compared with 2022, twice as much as the fall recorded each year between 2019 and 2022. This result is in line with France's decarbonization objectives for 2030: a 55% reduction in emissions compared with 1990 (the European Union's target).
The HCC calls for this trajectory to be consolidated, while expressing concern about the delay in publishing the legislation needed to implement decarbonization at national level.
Decarbonization involves reducing, or even eliminating, the consumption of fossil fuels to run an organization. This consumption leads to greenhouse gas emissions, which play a key role in the climate changes we are experiencing today, and their consequences (political, social, societal, economic and on ecosystems).
This article explores the impact of GHG emissions on climate.
1. What is the greenhouse effect?
1.2. The additional, or anthropogenic, greenhouse effect
1.3. Quantifying the impact of different GHGs on the climate
What is the greenhouse effect?
☁️Unnatural phenomenon
To understand the impact of greenhouse gases on the climate, we first need to look at the greenhouse effect.
The greenhouse effect is a natural phenomenon that retains infrared rays emitted by the sun and reflected by the earth's surface. Certain gases, known as "greenhouse gases", naturally present in the atmosphere, prevent some of these infrared rays from escaping back into space. It is these rays that contribute to global warming.
The greenhouse effect is a natural phenomenon. Without it, the Earth's average temperature would be -18°C, but thanks to this phenomenon, it is 15°C, making life as we know it possible.
🏭Theadditional, or anthropogenic, greenhouse effect
However, we need to distinguish between the natural greenhouse effect and the so-called "additionalgreenhouse effect" of anthropogenic (human) origin. Increased consumption of fossil fuels leads to increased GHG emissions, which are directly responsible for this "additional greenhouse effect", adding to the GHGs already present. This additional greenhouse effect is directly caused by the increase in fossil fuel consumption, and therefore by the increase in anthropogenic GHG emissions. Burning fossil fuels emits GHGs.
If GHG emissions increase, so does the concentration of GHGs in the atmosphere. This increase has been observed since the Industrial Revolution, a period of dazzling progress and radical changes in our lifestyles, due to the consumption of fossil fuels.
It creates an imbalance between the energy entering the atmosphere and the energy leaving it. This imbalance (the difference between incoming and outgoing energy) is called "radiative forcing", and is measured in watts per square metre. Since the industrial revolution, less energy can leave the atmosphere than enters it, due to the greater concentration of greenhouse gases, which retain more infrared rays.
A final piece of information to note about greenhouse gases is that they are composed of stable molecules. They do not react spontaneously with elements in the atmosphere (except for water vapor, which dissipates rapidly), and once emitted, they remain there.
Dissipation processes (photosynthesis, dissolution in the ocean, etc.) take time, and the lifetime of a GHG can range from 12 years (methane) to 50,000 years (halocarbons), via 100 years for carbon dioxide (CO2). This means that even if all GHG emissions stopped within a minute, the effects of GHGs already in the atmosphere would still be felt over several decades. At present, the IPCC is forecasting global warming until at least 2050.
We can conclude that :
- Global warming is irreversible.
- The consequences are only going toget worse.
🧮Quantifyingthe impact of different GHGs on the climate
When we talk about GHGs, we often mention CO2, but there are many other types:
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Ground-level ozone (O3)
- Halocarbons (CFC gases, used as refrigerants among other things)
- Water vapor (H2O)
These gases all have different global warming potentials (GWPs). In order to compare them, it is assumed that the GWP of CO2 is 1, and the GWPs of the other GHGs are calculated in relation to that of CO2.
For example, methane has a GWP of 25, making it 25 times more "powerful" than carbon dioxide. By way of comparison, nitrous oxide has a GWP of 298.
It should be noted that the water vapour emitted by human activities does not contribute to the greenhouse effect in a way that is detectable enough to be included in anthropogenic emissions.
This is also why we speak of "CO2 equivalents": to compare the impact of different GHGs on the climate, we reduce them to that of CO2.
Sources of GHG emissions
The sources of GHG emissions, whether for a country, an organization or an individual, are identified using a GHG emissions balance.
It enables the systematic evaluation of GHG emissions at national, organizational or individual level over one year, i.e. the quantification of their carbon footprint. It can also be seen as the identification of the physical flows on which the country, organization or individual depends to run their activities.
🇫🇷EnFrance
At national level, the aim of the carbon balance is to monitor the evolution of emissions in relation to international and national commitments.
For example, the European Union is aiming for a emissions by 55% by 2030 compared to 1990 levels.
As part of its national low-carbon strategy, France aims to achieve carbon neutrality by 2050, i.e. to emit as much as it absorbs. To achieve this, reduction targets have been set by sector: industry, agriculture, energy production, forests, wood and soil, buildings and transport.
The formats and methodologies used to collect GHG emissions at national level are those of the United Nations Framework Convention on Climate Change, and the SECTEN format in France.
The sources of GHG emissions at national level are :
- 🛢️La consumption of fossil fuels for transport, heating, energy production and conversion, and manufacturing. These processes emit carbon dioxide in particular.
- 🐮Agriculture, which emits CH4 (methane, from the anaerobic digestion of cattle in particular) and N2 (nitrous oxide, from the fertilizers used).
- 🧪Industrial processes and solvents used in the non-metallic minerals, semiconductor, food processing and cold chain industries. These uses emit carbon dioxide and fluorinated gases.
- ♻️Le waste treatment emits methane when waste is broken down, and CO2 when it is incinerated.
- 🌳LULUCF, or "land use, land use change and forestry". This category covers GHG emissions and removals resulting from human activities related to land use. Although LULUCF emissions are technically natural, they are considered anthropogenic because they are induced or conditioned by human activities (deforestation, afforestation, soil artificialisation, impacts of agricultural practices on soils, etc.). LULUCF can also be counted as a carbon sink in the national inventory.
France's carbon footprint is estimated at 623 million tonnes CO2 equivalent in 2022, with a per capita footprint of 9.2 tonnes CO2 equivalent. To achieve carbon neutrality by 2050, this per capita footprint needs to reach 2 tonnes CO2 equivalent.
🏢Forcompanies
Company emissions are identified using other assessment methodologies. There are 3 main ones:
- The GHG Protocol
- The regulatory method (BEGES, only in France)
- The Bilan Carbone® method (developed by ADEME and Jean-Marc Jancovici, in France).
There is also the ISO 14064-1: 2018 standard, which specifies guidelines for quantifying and reporting GHG emissions, and to which the regulatory method is aligned among other things.
The GHG Protocol defines the 3 scopes into which emission items are classified. With the other methods, the scopes have been refined into several categories:
- ⚡Direct energy emissions(scope 1)
- 🔌Energy-related indirect emissions(scope 2)
- 🚚Indirect emissions from transport (scope 3)
- 🛒Indirect emissionsfrom purchased products (scope 3)
- 💶Indirect emissionsfrom products sold (scope 3)
- ↕️Autres indirect emissions (scope 3).
Through these categories, we can identify several emission items, depending on the company being evaluated. Some items are relatively commonly identified (e.g. electricity and gasoline consumption), while others are genuinely company-specific (e.g. products bought or sold). For example, some companies buy wood, while others do not. Some sell furniture, others bicycles, still others services.
The formula used to assess a company's carbon footprint when carrying out a GHG assessment is :
Activity data x Emission factor.
Activity data is data indicating the company's consumption of an emission item. For example, liters of gasoline consumed on business trips, number of computers owned, euros spent on security...
Emissions factors are coefficients that convert these data into actual GHG emissions.
The consequences of GHG emissions
We need to reduce GHG emissions because they are the cause of climate change, and consequently have a considerable impact on the environment and our living spaces.
🔥Ground-scalewarming
Let's start with the most well-known: global warming. The Paris Agreement (2015) urges signatory countries to limit global warming to 2°C by 2100, 2°C being considered the limit that must not be exceeded to avoid climate runaway: the activation of irreversible feedback loops that would only exacerbate the disruption we are experiencing.
This warming is not simply a change from 30°C to 32°C in summer. A more apt analogy is that of human body temperature: a warming of 2°C on a global scale would be like going from 37°C to 39°C in body temperature. In other words, a radical change in living conditions.
Warmer temperatures on a global scale lead to a disruption of the climate system, resulting in more frequent and extreme weather phenomena. Fires, heatwaves, droughts, floods, displacement of animal populations and cyclones are just a few examples of what we're already experiencing every year: forest fires in Canada and Australia, heatwaves in France, India and Brazil, floods in northern France, droughts in southern France and Spain...
🪸Oceanacidification
The oceans are a natural carbon sink, meaning they naturally absorb carbon from the atmosphere. One way for CO2 to be purified from the atmosphere is to dissolve in the ocean.
In so doing, CO2 reacts with water to form molecules that contribute to a drop in ocean pH, and hence to acidification. Since the industrial revolution, the surface pH of ocean waters has fallen by around 0.1. This means that the water is about 28% more acidic.
Variations of the order of 0.2 pH units have already occurred, but over tens of thousands of years, giving marine ecosystems time to adapt.
Today's acidification is much more rapid, and poses many problems for the survival of marine species. For example, it can change the way sound is transported in water, and therefore the way certain species communicate. It disrupts the moulting of crabs and lobsters, and weakens corals. Above all, it disrupts the formation of limestone shells for organisms at the base of the food chain, leading to a disruption of marine and terrestrial biodiversity.
🧊Meltingice and rising sea levels
Another consequence of rising GHG emissions is the melting of ice, whether pack ice, ice caps or glaciers. The melting of these last two types of ice contributes to rising sea levels, because they add a volume that was not included in the initial volume (unlike pack ice).
In conclusion, rising GHG emissions are leading to climate change, which is radically altering the places we live, the environment we live in, and the resources on which we depend for our activities and lifestyles. We need to preserve our environment and its functioning if we are to continue to be able to carry out our activities in a sustainable manner and reduce the climate risk.
