Noctilucent clouds are the rarest and highest type, forming about 50 miles above the Earth’s surface.
Clouds that glow at night, shining against the night sky, have become more visible in recent years.
Every year from early June to early August, a type of cloud at the edge of space appears in the night sky at high latitudes.
Experts say that these mysterious glowing clouds are getting brighter and more visible over a wider area of the planet. The likely culprit: increased pollution from fossil fuels and rocket launches.
Noctilucent, or night-glow, clouds are the highest on Earth and form at altitudes of more than 50 miles above Earth’s surface, in an upper layer of our planet’s atmosphere called the mesosphere. The wispy bluish-white tendrils, stretching against the night sky, were first reported in 1885, two years after the Krakatoa volcano erupted.
“Clouds occur every summer, beginning in mid-May in the north and mid-November in the south,” said James Russell, co-director of the Center for Atmospheric Sciences at Hampton University in Virginia. Russell is also the principal investigator for NASA’s AIM mission, a satellite that has been observing noctilucent clouds from 370 miles above Earth’s poles since 2007.
Scientists believe that noctilucent clouds form when water molecules freeze around specks of smoke from burning meteorites in the atmosphere, forming ice crystals that make up the towering clouds. They are based on extremely cold temperatures and form in the summer, when temperatures in the mesosphere are lower than -180 degrees Fahrenheit.
In the 19th and 20th centuries, reports of noctilucent clouds were limited to the far north and south of the planet, in places like Canada and Alaska. But in recent years, they have turned up closer to the equator, in Colorado and Utah. In 2019, they were seen as far south as Joshua Tree in California.
“In the summer of 2019, the Northern Hemisphere clouds were especially bright and were seen more abundantly in the mid-latitudes,” Russell told Insider, adding, “So far, the current season appears to behave similarly to 2019.” .
Rising emissions of methane, a greenhouse gas that contributes to climate change, may be making them appear more frequently, according to Russell. One of the main sources of methane emissions is the burning of fossil fuels, according to the International Energy Agency.
When methane reaches the upper atmosphere, it breaks down by absorbing the sun’s rays and produces water vapor, Russell said. This extra water vapor creates ice crystals and forms noctilucent clouds. Noctilucent clouds can act like a canary in the coal mine for methane gas, according to Russell.
“This says that the rarefied upper atmosphere, literally at the edge of space, is a potential harbinger of key information about global change,” Russell said.
The researchers say rocket launches, which have become more common with the rise of commercial space travel, may also play a role in the rise of noctilucent clouds. When rockets leave Earth’s atmosphere, they leave behind water vapor as an exhaust. “In the last few days we saw a big spike in the clouds,” Cora Randall, a scientist and professor at the University of Colorado, told Spaceweather.com last week.
“We’re speculating that the spike could be due to additional water vapor carried to higher latitudes from rocket launches,” Randall said, though more analysis is needed to confirm whether rocket launches are creating more freak clouds.
Russell pointed to a growing body of research suggesting small, but statistically significant, long-term increases in methane and water vapor in the upper reaches of the atmosphere. Taken with increasing noctilucent clouds, “these results could be interpreted as an early indication of climate change at the edge of space,” Russell told Insider. Still, more data collected over a longer period of time is needed to draw definitive conclusions, he added.
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