+ 1.15°C: this is the difference in average global temperature in 2022 compared to the pre-industrial period. In the global warming court, greenhouse gases (GHGs) occupy the dock.

At their head, carbon dioxide (CO2). But it is not the only one responsible for global warming. Six greenhouse gases have been officially listed by the Kyoto protocol.

What are these greenhouse gases? What are their sources of emissions? How did human activity accelerate their concentration in the atmosphere? What is their environmental impact?

Here is an overview of the main greenhouse gases:

What is the greenhouse effect?

The greenhouse effect is a natural phenomenon, essential for life on Earth.

It was in the 19th century that this concept was theorized by the physicists and scientists Joseph Fourier, Tyndall and Arrhenius.

Their work successive results lead to the conclusion that the Earth's temperature varies according to the composition of the atmosphere, and in particular its CO2 content.

Present naturally in the atmosphere, greenhouse gases act like the windows in a greenhouse. They let pass The sun's rays by absorbing some of their heat. They also absorb thermal infrared radiation returned from the Earth's surface and maintain a temperature favorable to life on Earth. Without the greenhouse effect, the temperature would be 30°C lower, around -18°C.

The scientists Distinguish between the natural greenhouse effect and the anthropogenic greenhouse effect. This adjective refers to the greenhouse effect caused by human activity.

What are greenhouse gases?

Three greenhouse gases are naturally present in the atmosphere. Other industrial greenhouse gases only exist because humans made them.

Natural greenhouse gases

Carbon dioxide (CO2)

Carbon dioxide is the best known of the natural greenhouse gases. It is it that serves as a global standard for measuring GHG emissions in CO2 equivalent.

Carbon dioxide is the gas with the power of Global warming (GWP) the lowest. But it is the one who is the most present in the atmosphere, since long before the appearance of man.

The breathing of living beings and the decomposition of biomass Are natural sources of CO2. Essential for life on Earth, it is absorbed by plants to photosynthesize. Natural carbon sinks, forests and oceans have maintained the stability of the concentration of atmospheric CO2 for millions of years.

Methane (CH4)

Methane is one of the main components of natural gas. This gas is formed naturally during the decomposition of organic waste animal or vegetable, protected from oxygen, under the ground or in water.

Methane is also produced by... ruminant animals. Ingested plants ferment in their stomachs and release methane via their burps.

Although methane survives ten times shorter than CO2 in the atmosphere, its global warming potential (GWP) is 25 times higher.

Nitrous oxide or nitrous oxide (N2O)

Nitrous oxide or nitrous oxide is an oxygenated compound of nitrogen. Ses main natural sources are soils and oceans. When they decompose, plants release nitrogenous substances absorbed during their growth.

Nitrous oxide is a powerful greenhouse gas. Its global warming power (GWP) is 298 times higher than that of carbon dioxide and its survival in the atmosphere is estimated at 120 years.

Industrial greenhouse gases

Hydrofluorocarbons

Hydrofluorocarbons (HFCs) represent 90% of GHG emissions from fluorinated gases (F-Gas). Man-made, they are used for cooling, refrigeration, heat pumps or aerosols. They were developed in the 1990s to replace substances that destroy the ozone layer.

But today hydrofluorocarbons (HFCs) threaten the climate. With a global warming power (GWP) of the order of 120 to 14,800 times that of CO2, these greenhouse gases are very powerful air pollutants.

Other fluorinated gases

Three other fluorinated gases coexist with HFCs: perfluorocarbons (PFC), thesulphur hexafluoride (SF6) and the nitrogen trifluoride (NF3).

These gases are found in industrial production processes (perfluorocarbons and nitrogen trifluoride) or the insulation of power lines and double glazing (sulfur hexafluoride).

What is the impact of human activity on the greenhouse effect?

Natural greenhouse gas emissions are responsible for 90% of the anthropogenic greenhouse effect. Their concentration in the atmosphere has jumped by leaps and bounds since the pre-industrial era. The increase is estimated by the World Meteorological Organization (WMO) at 149%, 262% and 124% respectively for carbon dioxide, methane and nitrous oxide.

Human CO2 emissions

Human activities have disrupted the natural carbon dioxide cycle. They have created an imbalance between rising CO2 emissions into the atmosphere and declining absorption capacities of natural carbon sinks. Carbon dioxide is responsible for nearly 65% of the greenhouse effect is caused by humans.

According to the latest report by the International Energy Agency (IEA), global CO2 emissions reached a historic record in 2022, with 36.8 billion tons (Gt). Energy combustion is the sector that emits the most carbon dioxide, with an increase in emissions of 423 million tons between 2021 and 2022. Industry and agriculture follow on the second and third steps of the podium.

Human methane emissions

60% of the methane in the atmosphere is of anthropogenic origin. This gas is responsible for 15% of the greenhouse effect due to human activities.

The methane released into the atmosphere comes fromrearing, of the combustion of organic matter or the decomposition of household waste. It is also clear when of the extraction, transformation and transport of fossil fuels (coal, petroleum, natural gas), and by leaks on farms.

The IEA estimates that nearly 350 million tons of methane were emitted worldwide in 2022, 40% of which came from agriculture (142 million tons) and 38% from the energy sector (133 million tons).

Human emissions of nitrous oxide (N2O)

Nitrous oxide has seen its concentration in the atmosphere increase by 2% in 150 years. This gas is responsible for 5% of the anthropogenic greenhouse effect and contributes to the destruction of the ozone layer.

Les nitrogen fertilizers and livestock effluents are the main human source of nitrous oxide. In 2021, 89% of French N2O emissions came from agriculture. The State has set a goal of reducing them by 15% between 2015 and 2030. The annual reduction trajectory was defined by the decree of December 26, 2022, in application of the Climate and Resilience Law.

The chemical industry is the second source of nitrous oxide emissions. This gas is used for the production of citric and adipic acids. To a lesser extent, it is emitted by wastewater treatment and fuel combustion in the transport and energy sectors.

What is the environmental impact of greenhouse gases?

The strengthening of the greenhouse effect under the effect of human activities changes temperatures and changes the climate, with an environmental impact that is sometimes dramatic on ecosystems and biodiversity.

Global warming

Global warming is the most direct environmental impact of increased greenhouse gas emissions into the atmosphere. Elle reinforces the natural greenhouse effect, with the consequence of global warming of the planet.

2022 was the hottest year since 1850 on a global scale, with an average global temperature 1.15 °C higher than in the pre-industrial period. In France, the temperature difference between 2022 and the average recorded between 1961 and 1990 is + 2.7 °C.

Climate change and natural disasters

Heat waves, floods, dryness, hailstorms, torrential rains, devastating fires...: extreme climate events have been Multiplied by 5 since 1970 under the effect of climate change.

Since 2015, the World Weather Attribution (WWA) has been working on establish the cause-and-effect relationships between these disasters and global warming. The observation is relentless, as illustrated by two recent examples.

Following the massive fires in Canada in the spring of 2023, researchers concluded that extreme weather conditions favorable to forest fires were twice as likely to occur as a result of climate change. Likewise, they observe that extreme floods such as those that occurred in Libya in September 2023 had become up to 50 times more likely and up to 50% more intense than with a 1.2 °C cooler climate.

Sea Level Rise

Rising sea levels are one of the consequences of global warming. By 2050, the American Oceanic and Atmospheric Observing Agency (NOAA) estimates that sea level is expected to rise by 25 to 30 cm, which is as much as since 1880. The consequences could be dramatic for some islands, deltas and very low coastal areas.

Three phenomena explain the expected acceleration of the rise of the oceans: thermal expansion of water under the effect of heat, the Melting of the glaciers higher than the average and the disappearance of the ice caps in Greenland and Antarctica.

Consequences on ecosystems and biodiversity

Rising temperatures and climate change could reach a critical threshold for the environment and for many animal and plant species. Major ecological balances and land depletion are already being observed.

20 to 30% of species would be threatened with extinction. We are already seeing changes in travel animal species, with modified migrations and the rise to the north of parasitic, invasive and disease-carrying species.

At ocean level, theIncrease in ocean acidity disrupts fish and marine mammals and threatens coral reefs and some plankton and, beyond that, the balance of ecosystems.

What are the solutions to mitigate greenhouse gas emissions?

Greenhouse gases have been in the sights of the international community since the 1997 Kyoto Protocol. It was strengthened in 2015 by the Paris Agreement. It commits countries to reduce greenhouse gas emissions by 43% by 2030 to move towards net zero emissions.

The European Union and France are going further, with the objective of 55% reduction in greenhouse gases by 2030 And ofReach the carbon neutrality In 2050.

Addressing this ambitious challenge requires a Mobilization of all. Development of renewable energies, energy sobriety, ee, carbon-free electric mobility, low-carbon energy production, decarbonization of uses, capture of CO2 in the air, etc.: the national low-carbon strategies rely on several pillars to reduce CO2 and methane emissions into the atmosphere.

Fluorinated gases are also concerned. through the fight against global warming. In October 2023, a European agreement was reached to make them disappear by 2050. The timetable foresees a ban on hydrofluorocarbons in refrigerators as early as 2026 and in certain heat pumps and air conditioning systems starting in 2027.

The development of low-carbon infrastructures would have avoided the emission of 550 million tons of CO2 into the atmosphere in 2022. But The global effort of countries remains to be intensified to hope to preserve the environment and maintain “the increase in the global average temperature well below 2°C above pre-industrial levels”, an objective set by the Paris Agreement.