datalab
Key figures on climate
France, Europe and Worldwide
2023 EDITION
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Causes of climate change

The natural greenhouse effect and its disruption by human activities
Current energy flows in W/m2

Note: the Earth constantly receives energy from the sun. The part of this energy that is not reflected by the atmosphere, such as clouds or the earth's surface (oceans and continents), is absorbed by the earth's surface, which heats up by absorbing it. In return, surfaces and the atmosphere emit infrared radiation, the hotter the surface, the more intense the radiation. Some of this radiation is absorbed by certain gases and clouds, then re-emitted towards the surface, helping to warm it. This phenomenon is known as the greenhouse effect.
Sources: from Météo-France; IPCC, 1st Working Group, 2021

The increase in the atmospheric concentration of GHGs due to anthropogenic emissions (see glossary) increases the emission of energy towards the ground, leading to an imbalance in the Earth's energy balance and a rise in its surface temperature. The change in radiation induced by an element relative to a reference year is called radiative forcing. A positive radiative forcing indicates a positive contribution to global warming. The total anthropogenic radiative forcing amounts to + 3.8 W/m2 for GHGs and - 1.1 W/m2 for aerosols in 2019 compared with 1750, i.e. a net total of + 2.7 W/m2.

Greenhouse gases (GHG)

Excluding water vapor, GHGs occupy less than 0.1% of atmospheric volume. Water vapor, which fluctuates between 0.4% and 4%, is the main greenhouse gas. Human activities have very little direct impact on fluctuations in its concentration, but do have a strong impact on the concentrations of other GHGs.

CO2

Carbon dioxide

CH4

Methane

N2O

Nitrous oxide

HFC

Hydrofluorocarbons

PFC

Perfluorocarbons

SF6

Sulfur hexafluoride

NF3

Nitrogen trifluoride

Atmospheric concentration 2022* (in 2005 in brackets)

417ppm

(379ppm)

1,912ppb

(1,774ppb)

336ppb

(319ppb)

255ppt

(> 49ppt)

92.8ppt

(> 4.1ppt)

11ppt

(5.7ppt)

2.5ppt

(0ppt)

Global warming power (cumulative over 100 years)

1

28

265

[< 1 ;12,400] depending ongases

[< 1; 11 ,100] depending on gases

23,500

16,100

Source of anthropogenic emissions

Fossil fuel combustion, industrial processes and tropical deforestation

Landfills, agriculture, livestock farming and industrial processes

Agriculture, industrial processes, fertilizer use

Sprays, refrigeration, industrial processes

Manufacture of electronic components

Change in radiative forcing in 2022** since 1750 due to anthropogenic emissions (W/m2)

(in 2005 in brackets)

+2.17

(+1.66)

+ 0.65

(+ 0.59)

+ 0.193

(+ 0.14)

+ 0.05

(+ 0.02)

* In 2021 for HFC, PFC, SF6 , NF3 gases.
** In 2019 for HFC, PFC, SF6 , NF3 gases.
Note: ppm= part per million; ppb= part per billion; ppt= part per thousand billion.
Sources: IPCC, 2014; Agage, 2021; NOAA, 2023

Global Warming Potential (GWP, see glossary) is the ratio between the energy returned to the ground in 100 years by 1 kg of gas and that which would be returned by 1 kg of CO2 . It depends on the radiative properties and lifetimes of gases in the atmosphere. For example, 1 kg of methane (CH4) will warm the atmosphere as much as 28 kg of CO2 in the century following its emission. Although CO2 is the gas with the lowest global warming potential, it has contributed the most to global warming since 1750, due to the large quantities emitted.

GHG reservoirs and fluxes: the example of CO2 over the years 1750-2019 and 2011-2020

Note: this graph shows: (i) in square brackets, the size of reservoirs in pre-industrial times in billions of tonnes of CO2 in black, and their cumulative variation over the period 1750-2019 in red; (ii) in the form of arrows, carbon flows between reservoirs in billions of tonnes of CO2 equivalent per year (see glossary). Pre-industrial flows are shown in black. Those linked to anthropogenic activities between 2011 and 2020 are in red.
Sources: from IPCC, 1st Working Group, 2021; Friedlingstein et al., Global Carbon Budget 2021, 2022

Four major reservoirs store carbon in different forms:

  • atmosphere: CO2 gas;
  • terrestrial biosphere: soils and vegetation of forest, agricultural and peatland ecosystems...
  • ocean: limestone, dissolved CO2 ; marine flora and fauna (plankton);
  • subsoil: rocks, sediments, fossil fuels.

Carbon flows between these reservoirs originate from the natural carbon cycle, to which are added the disturbances linked to anthropogenic CO2 emissions (notably the combustion of fossil organic carbon reserves), which modify the exchanged flows or create new ones.

Imbalance between emissions and CO2 storage capacity
Net annual anthropogenic CO2 flows averaged over the period 2011-2021 (emissions to the atmosphere and uptake by terrestrial and oceanic reservoirs)

Note: the uncertainty for the increase in atmospheric CO2 concentration is very small (± 0. 02 Gt CO2 /year) and has not been represented on the graph.
Source: Friedlingstein et al, Global Carbon Budget, 2023

Over the last decade (2011-2021), of the 42 Gt CO2 generated on average per year by human activities, the atmosphere has absorbed almost 19 Gt, the terrestrial reservoirs (vegetation and soils) 12 Gt and the oceans 10 Gt. The atmosphere is the reservoir most affected by anthropogenic activities: it has absorbed almost 50% of the carbon emitted over the last sixty years.

Atmospheric CO2 concentration

Source: National Oceanic and Atmospheric Administration (NOAA), USA, 2023

Since the development of industrial activities, land and ocean reservoirs have absorbed more than half of anthropogenic emissions. The remaining emissions persist in the atmosphere, driving up GHG concentrations.

The role of the forest cycle on a global scale

On a global scale, forest land is a carbon sink. The gross sink attributed to the terrestrial biosphere - i.e. essentially to forests- offsets 29% of annual anthropogenic carbon emissions, or around 11 Gt CO2 (Friedlingstein et al., 2022). By integrating deforestation (forest land converted to other uses), the forestry sector becomes, conversely, a source of carbon. Deforestation leads to emissions linked to the loss of forest carbon stocks through the combustion and decomposition of organic matter. These net emissions (from forested land in particular) represent around 14% of annual anthropogenic carbon emissions worldwide (IPCC, 2022).

In France, net carbon sequestration in forest biomass is estimated at around 27.6 Mt CO2 eq for the year 2022, while the sink in wood products is 1.4 Mt CO2 eq. In total, forests and wood products have sequestered 7% of national GHG emissions (excluding land use, land-use change and forestry, LULUCF, see glossary) - (Citepa, 2023).