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Climate Change, or global warming, is caused by an ever-increasing amount of greenhouse gases (GHG) entering our atmosphere. The most abundant is carbon dioxide (CO2). Greenhouse gases form a “cloud” that traps Earth’s heat causing a Greenhouse Effect, slowly causing the global temperature to rise over time. Climate change is one of the most important environmental issues facing our planet.
The Greenhouse Effect
The greenhouse effect is the rise in the Earth’s temperature due to gases such as water vapour, carbon dioxide, nitrous oxide and methane that trap solar radiation in the atmosphere.
When sunlight enters the Earth’s atmosphere, it passes through a blanket of GHGs and is absorbed by the Earth’s surface. Some of this energy is reflected back into the atmosphere, but due to human-caused GHGs, this energy is increasingly being trapped in the atmosphere, causing global temperatures to rise.
Measuring greenhouse gases
There are many different types of GHG but there are a few principle GHGs that enter the atmosphere due to human activities: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases (e.g. HFCs, PFCs). These are the gases most commonly accounted for in GHG inventories and are typically measured in tonnes of carbon dioxide equivalent (tCO2e). All gases are converted to equivalent amounts of CO2 based on their global warming potential.
Though some gases such as sulfur oxides and nitrogen oxides have indirect global warming effects, six primary greenhouse gases (GHGs) are tracked and targeted for climate change mitigation:
CO2 – Carbon dioxide
CH4 – Methane
N2O – Nitrous oxide
PFCs – Perfluorocarbons
HFCs – Hydrofluorocarbons
SF6 – Sulphur hexafluoride
Global Warming Potential (GWP)
Global warming potential (GWP) is the ability of a gas to trap heat in the atmosphere. GWPs are important for comparing the impacts of GHG emissions and reductions of different gases. Each gas contributes to the greenhouse effect by a different magnitude, so assigning a GWP value for each gas provides a common unit for all GHGs.
Since carbon dioxide is the most prevalent GHG, it has a GWP of 1 and other gases are measured in terms of carbon dioxide equivalent (CO2e). A higher GWP means that a gas will remain in the atmosphere for a longer period of time. For example, methane has a GWP of 21, so the effect of one tonne of methane (CH4) released into the atmosphere is 21 times more powerful than one tonne of carbon dioxide (CO2).
Though different time scales may be used to calculate GWPs, standard practice is to use a 100-year time scale. To ensure consistency among GHG inventories and emissions calculations, standard practice applies GWP values from the UN Intergovernmental Panel on Climate Change (IPCC)’s Second Assessment Report (1996).