© NASA
This just in from NASA's AIM spacecraft: The sky above Antarctica is glowing electric blue. A ring of bright noctilucent clouds (NLCs) has formed around the South Pole, shown here in a Nov. 24th image taken by the spacecraft's Cloud Imaging and Particle Size (CIPS) Instrument:

"This season started on Nov. 17th, and is tied with 2013 for the earliest southern hemisphere season in the CIPS data record," says Cora Randall, a member of the AIM science team at the University of Colorado.

NLCs are Earth's highest clouds. They form more than 80 km above Earth's surface. Indeed, they are a mixture of Earth and space: Wisps of summertime water vapor rising from the planet below wrap themselves around meteoroids, forming tiny crystals of ice. Emphasis on summertime; NLCs appear on the eve of summer in both hemispheres.

There is growing evidence that noctilucent clouds are boosted by climate change. In recent years they have been sighted at lower latitudes than ever before, and they often get started in earlier months as well.

"The early start of the 2016 season was not at all a surprise," says Randall. "The southern hemisphere polar stratospheric winds switched to their summer-like state quite early this year."