Something magical appeared at evening over London and other parts of Britain on 21 June: ripples of electric blue clouds shimmered in the twilight sky just after sunset. These were being noctilucent clouds, the greatest clouds in the entire world, much more than 80km (50 miles) up on the edge of room, and appeared like some thing from another world.

Noctilucent clouds kind in the mesosphere, the rarefied upper atmosphere with tiny moisture and intensely low temperatures. The scant drinking water vapour there can freeze on to specks of smoke from meteors burning up in the environment, producing the crystals that sort noctilucent clouds. The mesosphere is coldest in summer, enabling the crystals to kind.

These clouds might also be a warning indicator of the local weather disaster. They have been initially recorded in 1885 and were almost never viewed for a long time afterwards, mostly in polar areas. But in new occasions the clouds have appeared significantly even more afield and are increasing substantially brighter.

A lot of the moisture wanted to kind the clouds will come from methane, a potent greenhouse fuel that produces water vapour when it breaks down in the upper atmosphere. And as methane air pollution has amplified, so noctilucent clouds have developed additional typical and additional widespread.