The Canadian Meteorological and Oceanographic Society (CMOS) is the non-profit scientific organization representing Canadian atmospheric and oceanic scientists and professionals.  Since 1963, the goal of CMOS has been the advancement of meteorology and oceanography in Canada.  CMOS has a special committee charged with the examination of timely scientific issues.

The Canadian Meteorological and Oceanographic Society , noting the longstanding controversy about local weather modification and more recent evidence of a changing climate, issues this policy statement for the information of all concerned.

Humans modify the weather deliberately and unintentionally.  An example of deliberate weather modification is the attempted change in local weather conditions (fog, low clouds and precipitation) by means of controlled, scientifically-based cloud seeding.  Unintentional weather modification includes the effects of industrial or agricultural activities on local weather, including air quality.  The focus of this statement is limited to deliberate or unintentional changes in local or regional weather conditions.  CMOS has a separate statement on global climate change.

CMOS recognizes that there are some clear cases of successful deliberate weather modification.  An example is the dissipation of supercooled fog and low stratus through seeding with ice-forming agents at selected airports.  However, clear statistical evidence and physical cause-and-effect relationships of the outcomes of planned weather modification are frequently difficult to establish.  Concerning unintentional weather modification, improved environmental monitoring and modelling capabilities have shown that human activities can have significant impacts on atmospheric parameters that influence our health and societal infrastructure.

CMOS supports efforts aimed at improving our understanding of the physical processes and determining the effects of planned and inadvertent weather modification.  Such studies have to be carried out on a scientific basis, in an environmentally responsible way.  There should be a concerted effort to improve the knowledge of the physical processes involved, to enlarge the data base, and to have an objective evaluation methodology of the impact.