Human-caused emissions of certain greenhouse gases contribute to a significant increase in the greenhouse effect and, consequently, in temperature: this is known as global warming.
Greenhouse gases (GHGs) are gases that, as their name suggests, contribute to the greenhouse effect. This is a natural phenomenon that warms the Earth. Without the greenhouse effect, the average temperature on Earth would be around –18 °C, according to the CNRS.
► Water vapor
Water vapor is a powerful natural greenhouse gas, but human-caused emissions of water vapor are considered negligible, and this gas is therefore not considered a major contributor to global warming. Furthermore, water vapor remains in the atmosphere for only a few days.
► Carbon dioxide (CO)2
Share of anthropogenic GHG emissions: 73 %
Atmospheric lifetime: > 100 years
French emissions in 2015: 336.6 Mt CO2eq.
PRG: 1
Main sources: fossil fuel combustion (heating, transportation, industry, etc.)
► Methane (CH)4
Share of anthropogenic GHG emissions: 20 %
Atmospheric lifetime: ~12 years
French emissions in 2015: 58.9 Mt CO2eq.
PRG: 28
Main sources: agriculture, livestock, and waste
► Nitrous oxide N2O
Share of anthropogenic GHG emissions: 5 %
Atmospheric lifetime: ~110 years
French emissions in 2015: 41.3 Mt CO2eq.
PRG: 265
Main sources: fertilizers and agriculture
► Fluorinated gases (hydrofluorocarbons, perfluorocarbons, etc.)
Share of anthropogenic GHG emissions: 2 %
Atmospheric lifetime: 12 to 50,000 years
French emissions in 2015: 20.3 Mt CO2eq.
PRG: from 6,000 to 23,500 (for sulfur hexafluoride)
Main sources: refrigerators, aerosol cans, fire extinguishers…
* Mt CO₂eq. = millions of metric tons of CO₂ equivalent2
** GWP = global warming potential = energy returned to the ground over 100 years by one kilogram of gas (reference value of 1 for CO2). For example, one kilogram of methane warms the atmosphere as much as 28 kg of CO2 (over the course of a century). Its greenhouse effect is therefore significantly greater.
Sources: Key Climate Figures – 2018 Edition, Ministry of Ecological Transition
