The 2011 severe atmospheric events conference, held on August 11-12, 2011, Hamburg, Germany, discussed climatic and environmental changes as a result of various kinds of huge injections of aerosols into the atmosphere and the possible consequences for the world population. Various sessions of the conference dealt with different aspects of large aerosol injections and severe atmospheric aerosol events along the geologic time scale. A presentation about radiative heating of aerosols as a self-lifting mechanism in the Australian forest fires discussed the question of how the impact of tropical volcanic eruptions depends on the eruption season. H.-F. Graf showed that cloud-resolving plume models are more suitable to predict the volcanic plume height and dispersion than one-dimensional models. G. Stenchikov pointed out that the absorbing smoke plumes in the upper troposphere can be partially mixed into the lower stratosphere because of the solar heating and lofting effect.
Huge amounts of aerosols can be generated by volcanic eruptions, forest fires, and asteroid impacts. They would also occur as a result of nuclear weapon explosions and subsequent fire storms. Climate engineering might make use of the strong effects of large amounts of aerosols with the goal of reducing the solar radiation that warms the atmosphere. These events were topic of an international conference1 of the Research Group Climate Change and Security (CLISEC) of KlimaCampus at the University of Hamburg and the King Abdullah University of Science and Technology, Saudi Arabia (KAUST). It was at the KlimaCampus of the University of Hamburg that, for the first time, one meeting included discussions of all kinds of aerosol sources in all aspects, from pathways and impacts to policies. The conference was divided into four sessions, each dealing with different aspects of large aerosol injections, and included a lecture by O. B. Toon about severe atmospheric aerosol events along the geologic time scale. The following summarizes the sessions.