PMCs (“polar mesospheric clouds”) in the northern hemisphere have become more frequent and brighter in recent decades—a development that may be related to climate change.
In the summer of 1885, sky watchers around northern Europe noticed something strange. Sunsets weren’t the same any more. The red and orange colors they were used to seeing were still there—but those familiar colors were increasingly joined by rippling waves of luminous blue.
At first they chalked it up to Krakatoa, which had erupted just two years earlier. The explosion of the Indonesian super volcano hurled massive plumes of ash and dust into the atmosphere more than 50 miles high, coloring sunsets for years after the blast.
Eventually Krakatoa’s ash settled, yet the rippling waves of luminous blue didn’t go away. Indeed, more than 100 years later, they are shining brighter than ever.
Today we call them, “noctilucent clouds” (NLCs). They appear with regularity in summer months, shining against the starry sky at the edge of twilight. Back in the 19th century you had to go to Arctic latitudes to see them. In recent years, however, they have been sighted from backyards as far south as Colorado and Kansas.
A new study published in the Journal of Geophysical Research (doi:10.1002/2015JD024439) confirms what some researchers have long suspected: PMCs in the northern hemisphere have become more frequent and brighter in recent decades—a development that may be related to climate change.