Noctilucent clouds over Tallin, Estonia.

(Arsty/Getty Images)

At a Glance

Noctilucent clouds are wispy luminescent high-altitude clouds that are particularly visible at dawn and dusk during the summer months.Researchers set out to determine whether the clouds are indicators of climate change.

Climate change is making nighttime high-altitude clouds more visible, a new study says.

(NLC) are wispy luminescent high-altitude clouds that are particularly visible at dawn and dusk during the summer months. They form when water vapor freezes around specks of dust from incoming meteors.

The highest clouds in the atmosphere, NCLareperiodically very bright in the night sky when the sun illuminates them from below the horizon.

Researchers from Germany'sLeibniz Institute of Atmospheric Physics set out to determine whether noctilucent clouds that initially form inthe middle atmosphere about 50 miles aboveEarth's surface are indicators of climate change.

Their findings published this weekinGeophysical Research Letters, a journal of the American Geophysical Union, confirmed that increasing greenhouse gas emissions from human activity is creating more water vapor that"significantly enhances the visibility of NLC."

The clouds were discoveredin 1885 after the eruption of Indonesia'sKrakatoa volcano, which sent massive amounts of , according to a press release.

“We speculate that the clouds have always been there, but the chance to see one was very, very poor, in historical times,” said Franz-Josef Lübken, an atmospheric scientist at the Leibniz Institute of Atmospheric Physics in Kühlungsborn and lead author of the study.

Sightings increased throughout the 20th century, leading scientists to speculate that climate change was having an impact on the formation of these nocturnal clouds.

The researchers came to their conclusions by using satellite observations and climate models to simulate the effects of increased greenhouse gases on noctilucent cloud formation over the past 150 years.

"Since the beginning of industrialization, the chance to observe a bright NLC has increased from just one per several centuriesto a few per year," the researchers wrote. "We conclude that NLCsare indeed an indicator for climate change."