I read a fascinating story about noctilucent clouds on EcoWorldy blog. Apparently, certain cloud formations have been appearing where they shouldn’t be:

My boss was in France on Bastille Day last week where the big event of the night actually became the sight of these strange glowing clouds – - like polar noctilucent clouds except they were not over the North Pole – but over Paris.

The story gets more interesting:

Over the last week, photographers in many places around the world outside the Arctic regions, have run outside to get photos of these strange Noctilucent (Night Glowing) clouds showing up this week from Poland to North Dakota:

So what does all this mean?

Formed by ice literally at the boundary where the earth’s atmosphere meets space 50 miles up, they shine because they are so high that they remain lit by the sun even after our star is below the horizon.

Noctilucent clouds are a fundamentally new phenomenon in the temperate mid-latitude sky, and it’s not clear why they’ve migrated down from the poles. Or why, over the last 25 years, more of them are appearing in the polar regions, too, and shining more brightly.

“That’s a real concern and question,” said James Russell, an atmospheric scientist at Hampton University and the principal investigator of an ongoing NASA satellite mission to study the clouds. “Why are they getting more numerous? Why are they getting brighter? Why are they appearing at lower latitudes?”

Is this strange change in the weather a sign of global change due to human causes? The EcoWorldy article does a great job in discussing the pros and cons, and Quite a few people seem to think so – particularly as these clouds were first observed only after the Krakatoa eruption in 1885:

… climate models have predicted that higher greenhouse gas emissions would cause mesosphere cooling, resulting in more frequent and widespread occurrences of noctilucent clouds.

But a competing theory is that larger methane emissions from intensive farming activities are producing more water vapour in the upper atmosphere where methane concentrations have more than doubled in the past 100 years.