Noctilucent clouds are by far the highest clouds seen on Earth, and they may also be a sign of a changing climate.

When and where you can see them

Noctilucent clouds are faint, wispy, wavy looking clouds that form much higher in the atmosphere than every other cloud you're used to seeing.

How much higher?

A standard commercial flight will reach a cruising altitude between 30,000 and 42,000 feet, roughly 6 to 8 miles.

The tops of the strongest thunderstorms can grow up to 75,000 feet, about 14 miles.

Noctilucent clouds form roughly 50 miles above the ground.

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They're typically only seen in summer at latitudes of 50 degrees or higher.

They're called noctilucent, meaning "night-shining", because you can only see them with your naked eye within about an hour before sunrise or after sunset, when twilight can make these blue-white tendrils visible.

So, you'll have to either get up before dawn or stay up after sunset and, in the Northern Hemisphere, be quite far north in June, July or August to have a chance to see these clouds.

(MORE: How to identify different types of clouds)

How they happen

The area where noctilucent clouds form is the coldest air anywhere in the atmosphere or on the Earth's surface.

That air about 50 miles above the ground can have temperatures colder than -184 degrees Fahrenheit in the summer. That's over 50 degrees colder than the record coldest surface temperature in Antarctica (-128.6 degrees).

When it's that cold, ice crystals can form even though there's so little water vapor. It's many times drier than air from the middle of the Sahara Desert.

But the water vapor also needs something to freeze on, and the only tiny bits available so high up are leftovers from falling meteors or volcanic dust.

These clouds were first recorded in 1885 after the Indonesian volcano Krakatoa erupted and hurled plumes of volcanic ash miles into the Earth's atmosphere.

Here are some recent examples

Most recently, National Weather Service forecasters noticed NLCs picked up by FAA live cams in Alaska.

This beautiful timelapse from Calgary, Alberta, showed these wavy looking NLCs across the horizon.

This Minnesota storm chaser caught a few NLCs well above the cirrus clouds and even an evening thunderstorm in Minnesota.

And satellites can even see these thin, wispy clouds seemingly at the edge of space, as happened in early July.

Sign of climate change?

These hauntingly beautiful clouds are being seen more often and at lower latitudes than the start of the Industrial Revolution. They've been seen as far south as Kansas, Utah, and in June 2012 at an observatory in southern Spain.

That could be a signature of climate change.

A 2018 modeling study estimated there is 40% more water vapor at the altitude where noctilucent clouds form today than in the late 1800s.

According to the study, that's largely because the atmosphere has double the amount of the greenhouse gas, methane, than it did 100 years ago. Methane reacts with UV radiation from the sun to produce water vapor.

More water vapor means more noctilucent clouds during the summer.

"Since the beginning of industrialization, the chance to observe a bright NLC has increased from just one per several centuries to a few per year," the researchers wrote.

Also, the 1885 eruption of Krakatoa injected massive amounts of water vapor high into the atmosphere, possibly a reason why noctilucent clouds were first discovered at that time.

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.