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The rare night-shining clouds seen in this photo are both forming more frequently and becoming brighter, trends that point to changes in the atmosphere linked to greenhouse gases.
Photograph ©2010 Jan Erik Paulsen. Graph by Robert Simmon, adapted from Latitude-dependent long-term variations in polar mesospheric clouds from SBUV version 3 PMC data. Caption by Holli Riebeek.
Published January 27, 2011
Data acquired July 15, 2010