These past days, I was thinking about a thing (I don't know if it was already mentionned in this way) : If the prolonged cooling of the upper atmosphere (stratosphere, mesosphere, thermosphere) has a significant impact, or not, in triggering an "ice age".
The scientists say, by satelites measures, that the cooling began in the early 1980'. The magnetic activity of our sun also began to decrease at the same period. The temperatures of the outer layers of the atmosphere are mostly influenced by the UV rays which fluctuate more or less depending on the sun's activity. Less UV rays lead to a prononced cooling.
There are more and more mesospheric clouds, and it seems to be the same thing for stratospheric clouds. We actually know that cometary dust plays an important role in the formation of mesospheric clouds. The temperature and the water vapor are the main factors for clouds formation. This past years, the water vapor has increase a little in the lower troposphere but has stagneted or even decreased in the upper atmopshere. So, the temperature must also be a main factor for the formation of such clouds by increasing the relative humidity/reducing saturated vapor pressure.
The amount of ozone in the stratosphere has also started to decease strongly since the 80s at all latitudes (except maybe in the equator where the ozone is mainly formed). Chlorofluorocarbons have certainly an impact (They destroy the ozone). (I think the C's have also spoken about this and said it was premeditated). Basically the stratosphere warms because of the interaction of ozone and UV radiations. Less uv rays because of a decrease in solar activity may mean less exothermic interactions with ozone therefore less heat and a cooling (which is increased by the impact of the Chlorofluorocarbons).
This cooling can enhance the formation of stratospheric clouds. This kind of clouds can also lead to releasing reactions of chloric acid which in turn destroys ozone to. It's like a vicious circle. At the end we have a cooling, less ozone and more energetics UV rays, which are not filtered and have an impact on dna, which reache the ground.
What follows seems quite interesting for me :
The upper atmosphere becoming denser because of cooling. And scientists have noticed that the troposphere tends to decrease, due to cooling of the upper atmosphere, which exert on it a higher pressure. This means that the cooling reaches an area considered as the upper troposphere. And I believe this can be observed objectively by the increasing of the number of condensation trails and their persistence since the end of the 90'. (Some people ans scientists say it is also at this time that global temperatures have begun to stagnate or decrease.)
One other thing that i have found in a book says :
One thing seems likely: the rapid growth of the differences between the troposphere and the upper layers can not proceed beyond a certain limit, as indicated by the laws of thermodynamics. An inversion can occur and even brutally.
So, after some research, I came to think that the increase in temperature differences between the different layers of the atmosphere, conditioned by solar activity, could take an important part in the triggering of a short or long "ice age" by increasing certain atmospheric phenomena through continuous and sudden cooling of the lower atmosphere. (Here I do not take into account celestials phenomena which can be off course related to all this).