Human activities in the last two centuries have been resulting in continuously growing level of man-made atmospheric pollution by trace gases, aerosols etc. An important group of polluting trace gases, so called greenhouse gases led by carbon dioxide, is expected to warm the troposphere and to cool higher layers of the atmosphere, including the mesosphere and thermosphere. Since the signal-to-noise ratio for the greenhouse gas effect is expected to be greater at higher atmospheric levels, the first unambiguous detection of the increasing greenhouse gas concentration effects on the atmosphere seems to be more probable at higher atmospheric levels than in the troposphere. To be able to determine unambiguously from those observations the natural changes and the greenhouse gas concentration increase induced changes in the atmosphere, we must know natural long-term changes of the atmosphere.
The greenhouse gas effect on the troposphere has carefully been studied within the World Climate Research Program (WCRP) of WMO. Several years ago, project SPARC (Stratospheric Processes and Their Role in Climate) was established to study related effects in the stratosphere and their impact on tropospheric climate. SPARC is now expanding into the lower mesosphere. However, investigations of greenhouse gas-induced and other long-term trends and changes at higher levels of the mesosphere, in the thermosphere and ionosphere have not been coordinated and have been lacking an official umbrella.
Informal meeting of scientists interested in the field, held during the IAGA Assembly in 1997, resulted in organizing the Workshop “Long-Term Changes and Trends in the Atmosphere”, held in Pune (India) in February 1999. The Workshop was followed by establishing this Working Group during the IUGG Assembly in Birmingham in July 1999.

The working group on VLF/ELF Remote Sensing of the Ionosphere and Magnetosphere (VERSIM) is an international group of scientists interested in studying the behaviour of the magnetosphere and ionosphere by means of ELF (300 Hz - 3 kHz) and VLF (3-30 kHz) radio waves, both naturally and artificially generated. The group was set up in 1975 by IAGA (International Association of Geomagnetism and Aeronomy) and URSI (International Union of Radio Science).
Originally the emphasis was on probing of the magnetosphere by whistlers, but later the scope became somewhat broader. The group aims to promote research in this field by facilitating the exchange of ideas, information and experience between active research workers and other interested scientists. This is done through regular meetings at IAGA and URSI Assemblies, and via thecirculation of a newsletter. The group has also been active in sponsoring scientific symposia at IAGA and URSI Assemblies, in areas relevant to its field of interest, and in coordinating observational campaigns.
At present the main subjects of interest include Plasma structures and boundaries - morphology and dynamics, Wave-particle and wave-wave interactions, Wave-induced particle precipitation, Wave propagation in magnetosphere and ionosphere, Sprites and the effects of lightning on the ionosphere.
There are currently almost 100 scientists from 21 different countries on the VERSIM mailing list.