Editing IPCC:AR6/Glossary (section)

=== <span class="glossary-term">Atmosphere</span> ===

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

<div class="glossary-definition">'''Definition:''' The gaseous envelope surrounding the Earth, divided into five layers – the troposphere which contains half of the Earth’s atmosphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere, which is the outer limit of the atmosphere. The dry atmosphere consists almost entirely of nitrogen (78.1% volume mixing ratio) and oxygen (20.9% volume mixing ratio), together with a number of trace gases, such as argon (0.93 % volume mixing ratio), helium and radiatively active greenhouse gases (GHGs) such as 2) carbon dioxide (CO (0.04% volume mixing ratio), 4) methane (CH, 2 O) nitrous oxide (N and 3) ozone (O. In addition, the atmosphere contains the GHG water vapour (H2O), whose concentrations are highly variable (0–5% volume mixing ratio) as the sources (evapotranspiration) and sinks (precipitation) of water vapour show large spatio-temporal variations, and atmospheric temperature exerts a strong constraint on the amount of water vapour an air parcel can hold. The atmosphere also contains clouds and aerosols.</div>
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