If the polar aurora are observed since the mists of time, it seems that the clouds noctulescent they appear at the end of the XIX century. We can expect to see them more and more frequently, if the stratospheric water vapor continues to increase.
A double concentration of carbon dioxide in the atmosphere it would increase, by itself, the average world temperature of 1,2ºC. However, climate is a dynamic science. The ocean, continental surfaces and the different layers of the atmosphere respond to this modification, enabling reactions that would raise the temperature world average from 2 to 4,5ºC.
The reaction of climate in relation to the increase in greenhouse gas emissions is well known by all, but the uncertainties persist in relation to the response of clouds to aerosol sprays, For example.
A model of forecast climate try to simulate as precisely as possible all these reactions that govern the evolution of the climate. An American research team has studied in detail one of them, ignored for a long time by the community: it involves the stratosphere, which would respond to the increase in temperature of the air on the earth's surface, increasing its amount of steam water.
El steam is a potent greenhouse gas, and this mechanism contributes to the increase in the air temperature.
More information - The hole in the ozone layer below the poles