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Noctilucent Clouds over Mongolia captured 9/10th July by Jonathan Shock (more images) at about 4am local time on a flight from Europe to Beijing. The view is to the south-west and Jupiter is near the horizon. This is another sighting of the unusually southern extent of this summer's noctilucent clouds. Very low temperatures near the mesopause are needed to form their microscopic ice crystals and, paradoxically, these occur in summer. Increasing concentrations of CO2 could be cooling the upper atmosphere. At low altitude CO2 increases temperatures, higher up it cools by radiating heat into space. Image ©Jonathan Shock, shown with permission.