So, the real spraying began around 1997. Chemtrails they call it.
Planned and Inadvertent Weather Modification Adopted by AMS Council 2 October 1998
3) Anthropogenic influences on meteorological and climatological conditions are far reaching and
significant. Economic development should be framed with an awareness of how each activity alters environmental processes and atmospheric conditions. Much is known about the physical processes involved in many aspects of inadvertent weather modification, but important questions remain. Continuing research and monitoring related to inadvertent weather modification is required, and the breadth of these studies must be extended to include new knowledge on natural feedbacks and societal ramifications, which will lead to policy decisions that reduce the chance of severe impacts.
© 1998 American Meteorological Society
The above is from an article called "Planned and Inadvertent Weather Modification"