After three years of dodging Senate inquiries, the Department of Defense, on March 20, 1974, presented a subcommittee of the Senate Committee on Foreign Relations with a briefing on the extensive rainmaking operations in Southeast Asia. The briefing was classified "Top Secret," but the hearing report was made public on May 19, 1974. In this way the American public officially learned for the first time that the United States had used a new and developing technology in an attempt to slow movement of North Vietnamese troops and supplies along the Ho Chi Minh Trail network. From March of 1967 until July of 1972 the Air Force had rained canisters of silver iodide into clouds, and these in turn were supposed to initiate an increase in rainfall.

So began geoscientist Gordon J. ­MacDonald's 1975 essay for TR on weather modification. Although the revelation of the Vietnam War program was the occasion for his article, his concerns were more general. MacDonald, who died in 2002, was then a professor at Dartmouth and had served on the President's Science Advisory Committee under Lyndon B. Johnson. Throughout his career, he was interested in the way the planet changes as a result of both natural processes and human interference. After World War II, it became clear that industrial activity was changing the world's climate. If humans were inadvertently creating climate change, it followed that they might be able to reverse those effects by modifying the local weather (see "The Geoengineering Gambit").