It's summer at the South Pole, which means it's time for the frozen continent's noctilucent clouds to make an appearance. But over the last several decades, these beautiful electric blue clouds have been appearing earlier than usual — and they're getting bigger. It's yet another example of climate change at work.
Noctilucent clouds, or NLCs, are the highest clouds known to science, forming at the edge of space some 50 miles (83 km) above the Earth's surface. They're seeded by disintegrating meteoroids and form when sunlight hits the tiny ice crystals that make up the clouds. At times they appear to glow a mesmerizing electric blue.