This image illustrates where the troposphere ends abruptly at the tropopause, which appears in the image as the sharp boundary between the orange- and blue- colored atmosphere. The silvery-blue noctilucent clouds extend far above the Earth's troposphere. (NASA/Getty Images)

Noctilucent clouds are a mysterious marvel of the night sky. The beautiful blue ice clouds are a rare sight to behold, but are they pointing to something sinister in the atmosphere?

According to NASA,sent tons of volcanic ash high into the atmosphere. Since then, the clouds that form high in the atmosphere (nearly 50 miles above Earth’s surface) are a sight traditionally reserved for summer nights in far north regions like Russia and Scandinavia.

They are only visible a few weeks out of the year when atmospheric conditions are perfect. “Noctilucent season” generally falls between the beginning of June and the end of July.

But according to USA Today, . So why are they appearing so far south?Some scientists say it's a sign that noctilucent clouds could be linked to climate change. Produced in the mesosphere or upper atmosphere where clouds generally struggle to form, scientists think that greenhouse gases may be aiding in the creation of the noctilucent clouds.

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While greenhouse gasses generally warm the atmosphere, they serve as a cooling agent when they reach the mesosphere which could play a significant role in making more of the icy clouds. This is only one theory and as atmospheric researcher Tony Phillips tells SF Gate,

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Lenticular Cloud Over Mt. Rainier in Washington

Credit: National Park Service Facebook