Understanding the Basics
Core definitions, examples, and reference tables.
What are greenhouse gases?
These are gases that trap heat in the Earth’s atmosphere, influencing global temperature patterns. Some greenhouse gases (GHGs) are naturally occurring in the atmosphere and some are synthetic.
Table 1
Greenhouse gases: Sources and contribution to Canada’s total GHG emissions
| Greenhouse Gas | Sources | Proportion of Canada’s total GHG emissions in 2022* |
|---|---|---|
| Water vapour (H20) | The most abundant greenhouse gas and a key part of the water cycle. Created through the process of evaporation or sublimation of liquid water, most scientists believe that water vapour produced by human activity contributes very little to the amount of water vapour in the atmosphere. ** | Not measured |
| Carbon dioxide (CO2) | Arises through natural processes such as animal respiration and plant decomposition as well as human activities such as fossil fuel combustion, deforestation, and various industrial activities. | 78% |
| Methane (CH4) | Arises from natural sources like wetlands as well as human activities such as livestock farming, waste decomposition, and oil and gas extraction. | 17% |
| Nitrous oxide (N2O) | Arises from natural sources associated with the nitrogen cycle as well as agricultural and industrial activities, particularly fertilizer use and combustion processes. | 4% |
| Hydrofluorocarbons (HFCs) | Synthetic (man-made) gases that are used in refrigeration, air conditioning, and aerosol applications. | 1.6% |
| Perfluorocarbons (PFCs) | Synthetic gases that are used in aluminum production and electronics manufacturing. | |
| Nitrogen trifluoride (NF3) | A synthetic gas primarily used in the production of semiconductors and flat-panel displays. | |
| Sulphur hexafluoride (SF6) | A synthetic gas used in electrical transmission and insulation. |
* Source:
Government of Canada. National Inventory Report 1990-2022: Greenhouse Gas Sources and Sinks in Canada Part 1.
https://publications.gc.ca/collections/collection_2024/eccc/En81-4-2022-1-eng.pdf.
** Source: Climate Change Connection. What About Water Vapour?
https://climatechangeconnection.org/science/what-about-water-vapour/.
What is the greenhouse effect?
The greenhouse effect is a natural phenomenon that helps regulate the Earth’s temperature. Just like a greenhouse retains heat to support plant growth, the Earth’s atmosphere traps heat through the presence of greenhouse gases. This process is essential for maintaining a climate that supports life. Without the greenhouse effect, the planet would be significantly colder and unable to sustain current ecosystems.
Increases in greenhouse gas concentrations can intensify the greenhouse effect, leading to temperature shifts and climate variations. The energy balance between incoming sunlight and outgoing heat radiation is altered, which can contribute to various environmental changes. These changes include fluctuations in weather patterns, shifts in ocean temperatures, and modifications in precipitation cycles.
What is climate change?
The Intergovernmental Panel on Climate Change (IPCC) defines climate change as:
A change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings such as modulations of the solar cycles, volcanic eruptions, and persistent anthropogenic changes in the composition of the atmosphere or in land use.*
What does this mean in practice? Greenhouse gases, such as carbon dioxide and methane, play a role in regulating atmospheric temperatures. Changes in their concentrations can influence weather patterns, precipitation levels, and long-term climate trends.
* Source: IPCC, 2023: Annex I: Glossary [Reisinger, A., D. Cammarano, A. Fischlin, J.S. Fuglestvedt, G. Hansen, Y. Jung, C. Ludden, V. Masson-Delmotte, R. Matthews, J.B.K. Mintenbeck, D.J. Orendain, A. Pirani, E. Poloczanska, and J. Romero (eds.)]. In: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, pp. 119-130, doi:10.59327/IPCC/AR6-9789291691647.002.
https://www.ipcc.ch/report/ar6/syr/downloads/report/IPCC_AR6_SYR_AnnexesIndex.pdf.
What is “global warming potential” (GWP)?
Global warming potential (GWP) is a number that shows how much heat a greenhouse gas traps in the atmosphere compared to carbon dioxide over a set period, usually 100 years. Carbon dioxide is given a GWP of 1, and other gases are measured against it. For example, nitrous oxide has a GWP of 273 over 100 years. This means 1 tonne of nitrous oxide traps the same amount of heat as 273 tonnes of carbon dioxide.
Table 2
Select global warming potential (GWP) values
| Greenhouse Gas | Global Warming Potential (GWP)* |
|---|---|
| Carbon dioxide (CO2) | 1 |
| Methane (CH4) | 27 (emissions from non-fossil fuel sources) 29.8 (emissions from fossil fuel sources) |
| Nitrous oxide (N2O) | 273 |
| Nitrogen trifluoride (NF3) | 17,400 |
| Sulphur hexafluoride (SF6) | 24,300 |
* Source: IPCC Global Warming Potential Values, Version 2.0, August 7, 2024 (
https://ghgprotocol.org/sites/default/files/2024-08/Global-Warming-Potential-Values%20%28August%202024%29.pdf)
What is “carbon dioxide equivalent” (CO2e)?
Carbon dioxide equivalent (CO₂e) is a standard unit of measurement used to compare the impact of different greenhouse gases by expressing them in terms of the amount of carbon dioxide that would cause the same amount of warming. For example, nitrous oxide traps about 273 times more heat than carbon dioxide over 100 years. This means 1 tonne of nitrous oxide has the same warming effect as 273 tonnes of CO₂, so it would be counted as 273 tonnes CO₂e.
What does “net zero” mean?
The term “net zero” refers to the goal of balancing human-caused greenhouse gas (GHG) emissions with actions that remove or offset them. Achieving net zero emissions does not mean eliminating all GHG emissions – the objective is to reduce them as much as possible and compensate for any remaining emissions through alternative approaches such as carbon capture technologies, reforestation, or carbon credit programs.
What is Canada’s “net zero” target?
The Government of Canada has committed to achieving net-zero emissions by 2050 through the
Canadian Net-Zero Emissions Accountability Act.
Source: Government of Canada. Net-zero emissions by 2050.
https://www.canada.ca/en/services/environment/weather/climatechange/climate-plan/net-zero-emissions-2050.html.
