Long-term change in the upper atmosphere

The upper atmosphere may contain signatures of long-term global change in its physical and chemical behaviour. Robust data sets from the ionosphere, mesosphere and stratosphere can be compared with, for example, the solar cycle and the geomagnetic field. We discuss in particular the shrinking of the ionospheric F-layer and the cooling of the mesosphere, both trends consistent with global warming at lower levels. We also assess the usefulness of long-term records for observations of unpredicted, short-lived events. Carefully acquired, accurately calibrated, and well archived data sets spanning decades are used in order to evaluate either slow trends such as ionospheric cooling or unexpected happenings such as volcanic eruptions.