SSomething magical appeared at night over London and other parts of Great Britain on June 21: ripples of electric blue clouds gleamed in the twilight sky after sunset. These were noctilucent clouds, the highest clouds in the world, more than 80 km (50 miles) at the edge of space, and looked like something from another planet.
Noctilucent clouds form in the mesosphere, the upper atmosphere rarefied with little humidity and extremely low temperatures. The scant water vapor there can freeze and turn into specks of meteorite smoke that burn in the atmosphere, creating crystals that form noctilucent clouds. The mesosphere is colder in summer, allowing crystals to form.
These clouds can also be a warning sign of the climate crisis. They were first recorded in 1885 and were rarely seen for years afterward, mainly in the polar regions. But in recent times, clouds have appeared much further and are getting much brighter.
Much of the moisture needed to form clouds comes from methane, a powerful greenhouse gas that produces water vapor when it breaks down in the upper atmosphere. And as methane pollution has increased, noctilucent clouds have become more common and more widespread.
.
