Strange blue lights glowing on the edge of space first appeared over polar regions in 1885 and today, sightings are becoming increasingly common, and now the phenomenon is moving into lower latitudes including Northern California. Like the proverbial canary in the coal mine, these glowing space clouds may be a celestial siren, warning of Earth's global warming, according to some scientists. They're called "noctilucent clouds" or NLCs, basically, clouds that glow at night. They appear mainly in northern latitudes, about 50 miles above earth as miniscule droplets of water reflect the sun on the other side of the globe. Now,...