A related phenomenon involves the increasing number of cumulus clouds being reported and photographed by the general public. This is another clear sign that water vapor is being driven up to higher altitudes than normal, allowing the sun to illuminate them even after it has set from the observer’s perspective.
4.2. Atmospheric magnification effects
A second observation building up our argument involves visible distortion caused by the increases in water vapor density in the upper atmosphere that are caused by aircraft-produced vortices. Water vapor at different altitudes creates atmospheric disturbances, and these can focus the sun in a manner similar to a magnifying glass or a Fresnel lens (\citet{Owens_1967}; \citet{Tang_1994})28,29.
This has two consequences of particular interest. First, the distortions are sometimes visible as parahelia in the upper atmosphere (Figure \ref{549655}), due to the multilens effect caused by the presence of water vapor at higher-than-normal altitudes \citep*{McDowell_1974}30. Second, it increases global surface temperatures in certain areas and decreases it in others.