Editing IPCC:AR6/Glossary (section)

=== <span class="glossary-term">Greenhouse gas emission metric</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGIII</div>

<div class="glossary-definition">'''Definition:''' A simplified relationship used to quantify the effect of emitting a unit mass of a given greenhouse gas (GHG) on a specified key measure of climate change. A relative GHG emission metric expresses the effect from one gas relative to the effect of emitting a unit mass of a reference GHG on the same measure of climate change. There are multiple emission metrics, and the most appropriate metric depends on the application. GHG emission metrics may differ with respect to: (i) the key measure of climate change they consider; (ii) whether they consider climate outcomes for a specified point in time or integrated over a specified time horizon; (iii) the time horizon over which the metric is applied; (iv) whether they apply to a single emission pulse, emissions sustained over a period of time, or a combination of both; and (v) whether they consider the climate effect from an emission compared to the absence of that emission or compared to a reference emissions level or climate state. [Note:Most relative GHG emission metrics (such as the g lobal warming potential (GWP), global temperature change potential (GTP), global damage potential, and GWP*), use carbon dioxide (CO 2) as the reference gas. Emissions of non-CO2 gases, when expressed using such metrics, are often referred to as ‘carbon dioxide equivalent’ emissions. A metric that establishes equivalence regarding one key measure of the climate system response to emissions does not imply equivalence regarding other key measures. The choice of a metric, including its time horizon, should reflect the policy objectives for which the metric is applied.]</div>
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