Editing Greenhouse effect (section)

=== Lapse rate ===
{{Further|Lapse rate}}
In the lower portion of the atmosphere, the [[troposphere]], the air temperature decreases (or "lapses") with increasing altitude. The rate at which temperature changes with altitude is called the ''[[lapse rate]]''.<ref name="Nugent5">{{cite web |last1=Nugent |first1=Alison |last2=DeCou |first2=David |title=ATMOSPHERIC PROCESSES AND PHENOMENA: Chapter 5: Atmospheric Stability |url=http://pressbooks-dev.oer.hawaii.edu/atmo/chapter/chapter-5-atmospheric-stability/ |access-date=31 May 2023}}</ref>

On Earth, the air temperature decreases by about 6.5&nbsp;°C/km (3.6&nbsp;°F per 1000&nbsp;ft), on average, although this varies.<ref name="Nugent5" />

The temperature lapse is caused by [[convection]]. Air warmed by the surface rises. As it rises, air [[adiabatic process|expands and cools]].  Simultaneously, other air descends, compresses, and warms. This process creates a vertical temperature gradient within the atmosphere.<ref name="Nugent5" />

This vertical temperature gradient is essential to the greenhouse effect. If the lapse rate was zero (so that the atmospheric temperature did not vary with altitude and was the same as the surface temperature) then there would be no greenhouse effect (i.e., its value would be zero).<ref name="ThomasStamnes1999">{{cite book |last1=Thomas |first1=Gary E. |last2=Stamnes |first2=Knut |title=Radiative Transfer in the Atmosphere and Ocean |date=1999 |publisher=Cambridge University Press |isbn=0-521-40124-0}}</ref>