WMO STATEMENT ON WEATHER MODIFICATION
INTRODUCTION
For thousands of years people have sought to modify weather and climate
so as to augment water resources and mitigate severe weather. The modern
technology of weather modification was launched by the discovery in the
late 1940s that supercooled cloud droplets could be converted to ice
crystals by insertion of a cooling agent such as dry ice or an
artificial ice nucleus such as silver iodide.
Over 50 years of subsequent research have greatly enhanced our knowledge
about the microphysics, dynamics and precipitation processes of natural
clouds (rain, hail, snow) and the impacts of human interventions on
those processes.
Weather modification generally involves two distinct activities. In the
first activity, science research seeks to prove concepts and in so-doing
make the effectiveness of their application certain to within given
limits and with a given degree of confidence. In the second activity,
operational programs seek to apply different modification methods to
produce a desired outcome (more rain, less hail, fog cleared, etc.)
based on their assessment of the best approaches to follow consistent
with the current state of knowledge. Some operational programs also
include an evaluation component, but
generally only as a lower priority. Such evaluations, however, have the potential to add scientific insight.
In recent years there has been a decline in the support for
weather modification research, and a tendency to move directly into
operational projects. It is crucial to recognize that weather
modification is still an emerging technology. Uncertainties inherent in
the current technologies can only be addressed by programmes of focused
research that lead to deeper understanding of the effects of cloud
seeding on cloud and precipitation development.
Currently, there are dozens of nations operating hundreds of
weather modification projects, particularly in arid and semi-arid
regions all over the world, where the lack of sufficient water resources
limits their ability to meet food, fibre, and energy demands...