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What are greenhouse gases?

There are a number of different greenhouse gases being emitted into the atmosphere and causing climate change through the greenhouse effect.
A power plant emitting greenhouse gassses
The main GHGs are outlined below.
  1. Carbon dioxide (CO2) – Certainly the most well-known of the GHGs (we often abbreviate to talk about a “carbon reduction strategy” when we are really talking about a strategy to reduce all GHG emissions) as it makes up around 80% of all GHG emissions. This is due to it being generated when we burn fossil fuels to generate power or manufacture cement (and other common, large scale activities)
  2. Methane (CH4) – Famously generated by livestock as well as other farming activities and landfill decay. Methane makes up around 10% of the GHGs
  3. Nitrous oxide (N2O) – Generated through various agricultural activities, fossil fuel combustion and water treatment processes. Nitrous Oxide makes up around 7% of the GHGs
  4. Fluorinated gases – This is a range of gases with very long names such as Hydrofluorocarbons, perfluorocarbons, sulphur hexafluoride, and nitrogen trifluoride! These make up around 3% of emissions but are the most potent form a global warming perspective.

Converting them all to a common unit

Although CO2 is the most common GHG it is not the most powerful from a global warming perspective. In fact, it is estimated that 1 tonne of Hydrofluorocarbons is equivalent to over 1,800 tonnes of CO2. One tonne of methane is not as bad as that but it is still estimated to be the equivalent of around 25 tonnes of CO2 in terms of its impact as a greenhouse gas.
To make it much easier to measure and compare carbon footprints, all emissions are converted into “Carbon Dioxide Equivalent” which is written as “CO2e”. So when people abbreviate things and say “our carbon footprint is X tonnes” or “our carbon footprint is Y tonnes of CO2” what they are actually referring to is CO2e.
Here’s a common diagram used to show the difference:
Diagram showing Scope 1, 2 and 3 emissions
(Click to expand)
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