Trends in the neutral and ionized upper atmosphere

They cause warming in the troposphere but cooling in the upper atmosphere. Greenhouse gases such as carbon dioxide are not the only driver of long-term changes and trends in the upper atmosphere and ionosphere. Anthropogenic changes of stratospheric ozone, long-term changes of geomagnetic and solar activity, and other drivers play a role as well, although greenhouse gases appear to be the main driver of long-term trends.

This makes the pattern of trends more complex and variable. A consistent, although incomplete, scenario of trends in the upper atmosphere and ionosphere is presented. Trends in F2-region ionosphere parameters, in mesosphere-lower thermosphere dynamics, and in noctilucent or polar mesospheric clouds, are discussed in more detail.

Advances in observational and theoretical analysis have explained some previous discrepancies in this global trend scenario. An important role in trend investigations is played by model simulations, which facilitate understanding of the mechanisms behind the observed trends.