The signs and symptoms of climate change can be seen everywhere, even at the edge of space. On Spaceweather.com, Dr. Tony Phillips writes about the phenomenon of noctilucent clouds and how their increasing brilliance may signal changes in the atmospheric composition:
They appear with regularity in summer months, shining against the starry sky at the edge of twilight. Back in the 19th century you had to go to Arctic latitudes to see them. In recent years, however, they have been sighted from backyards as far south as Colorado and Kansas.
Noctilucent clouds are such a mystery that in 2007 NASA launched a spacecraft to study them. The Aeronomy of Ice in the Mesosphere satellite (AIM) is equipped with sensors specifically designed to study the swarms of ice crystals that make up NLCs. Researchers call these swarms “polar mesospheric clouds” (PMCs).
Source: National Weather Service
It’s a fascinating story, discovering that climate change means the mesosphere actually becomes icier, as he notes here from a 36 year long data record:
At altitudes where PMCs form, temperatures decreased by 0.5 ±0.2K per decade. At the same time, water vapor increased by 0.07±0.03 ppmv (~1%) per decade. …
These results are consistent with a simple model linking PMCs to two greenhouse gases. First, carbon dioxide promotes PMCs by making the mesosphere colder. (While increasing carbon dioxide warms the surface of the Earth, those same molecules refrigerate the upper atmosphere – a yin-yang relationship long known to climate scientists.) Second, methane promotes PMCs by adding moisture to the mesosphere, because rising methane oxidizes into water.
Speaking of CO2, how is it doing? From the Mauna Loa station:
