Greenhouse gases (GHGs) are gases which trap the sun’s warmth within the Earth’s atmosphere. GHGs include carbon dioxide (CO₂), methane, nitrous oxide, and fluorinated gases such as hydrofluorocarbons, perfluorocarbons, and sulphur hexafluoride.[1] Water, or hydrogen dioxide, is also a GHG.[2]

How are GHGs related to the climate?

Under normal circumstances, atmospheric levels of GHGs are fairly stable over time, keeping the temperature on Earth fairly stable over time as well. Indeed, GHGs are part of the reason that Earth’s temperature does not become too cold. However, due to human activities, large quantities of GHGs have been and continue to be emitted into the atmosphere, causing what is referred to as the “greenhouse effect”. The greenhouse effect is where more energy from the sun is trapped within the atmosphere than is being taken out of it, which causes the Earth’s temperature to rise.[3] This temperature rising, in turn, causes events associated with climate change, such as polar-ice melt which contributes to sea-levels rising, and increased frequency of acute weather events such as hurricanes, floods, and droughts.[4]

Key GHGs

…emitted through human activity

• Carbon dioxide: The burning of fossil fuels, among other human activities, has dramatically increased the rate of CO₂ emissions into the Earth’s atmosphere.[5] Click here to view the Keeling Curve, which shows how atmosphere CO₂ levels have increased dramatically over time.[6]
• Methane: Farming and oil and gas production are large sources of the release of methane.[7]
• Nitrous oxide: Though it is released by human activity in much smaller quantities than carbon dioxide, nitrous oxide has a much greater capacity to retain energy than carbon dioxide, making it a potent GHG when considering the impacts of its release into the atmosphere on climate change.[8]

…indirectly tied to human activity

• Hydrogen dioxide (Water): Water vapour, primarily evaporation from our oceans, is not directly released by human activity, as opposed to the other GHGs. It is nonetheless a very potent GHG. Water vapour is released at a faster pace when the surface temperature of the Earth becomes warmer; as the climate becomes warmer due to the release of human-related GHG emissions, more water vapour is released into the atmosphere, which in turn reflects the sun’s warmth back to the Earth’s surface.[9]

Mitigating climate change by reducing GHG emissions

GHG emissions are one of the most important factors when it comes to the causes of climate change and the solutions to halting the climate’s temperature increase. International agreements which aim to halt the progress of climate change, such as the Paris Agreement, are explicit that greenhouse gas emission cuts are essential (Art 2(1)(b); Art 4(1)). Legislation seeking to tackle climate change usually includes a cap on GHG emissions. The reduction of GHG emissions, along with increasing the resiliency of the cities we live in and adapting, is an essential ingredient in mitigating the impacts of climate change.

[1] See David Suzuki Foundation, “What are greenhouse gases?”, online: David Suzuki Foundation <https://davidsuzuki.org/what-you-can-do/greenhouse-gases/>.

[2] See Michael Mann, “Greenhouse gas: Atmospheric science” (Oct 29 2021), online: Encyclopedia Britannica <https://www.britannica.com/science/greenhouse-gas>.

[3] David Suzuki Foundation, supra note 1.

[4] Ibid.

[5] Michael Mann, supra note 2.

[6] Ibid.

[7] David Suzuki Foundation, supra note 1.

[8] Ibid.

[9] Michael Mann, supra note 2.