"...the release to the atmosphere of a gas that has an insulating effect of trapping heat radiating back from the Earth's surface..."

What are Emissions?

In very simplistic terms (and for the purpose of the ACX framework), a Greenhouse Gas (GHG) emission is the release to the atmosphere of a gas that has an insulating effect of trapping heat radiating back from the Earth's surface (similar in concept to the glass roof of a greenhouse). While the presence of these insulating gases makes the Earth warm enough to sustain life, if their concentration becomes too great the subsequent warming effect (the enhanced greenhouse effect) has the potential to change global climate systems.

There is a natural cycle of release and removal of these gases to and from the atmosphere. This is commonly referred to as the Carbon Cycle. The enhanced greenhouse effect occurs when the natural carbon cycle has been augmented by human activity (anthropogenic) which:

releases more carbon into the atmosphere (i.e. the burning of fossil fuels);

reduces the environment's capacity to remove Carbon from the atmosphere (i.e. the clearing of forests); and the concentration of GHGs in the atmosphere increases.

Not all GHG's have the same insulating effect. For example climate scientists attribute methane with a greenhouse effect that is 21 times (by weight) to that of carbon dioxide. For accounting purposes GHG emissions, reduction and offsets are measured and expressed in tonnes of carbon dioxide equivalent (CO₂e), standardising the greenhouse effect of a given quantity (by weight) of gas.