But though man cannot at his pleasure command the rain and the sunshine, the wind and frost and snow, yet it is certain that climate itself has in many instances been gradually changed and ameliorated or deteriorated by human action. George Perkins Marsh, "Address Delivered Before the Agricultural Society of Rutland County, Sept. 30, 1847," page 11.
George Perkins Marsh, polymath, intellectual leader, "Prophet of Conservation"*, a US Congressman form Vermont, at the time, gave this foundational speech about the impacts of agriculture and human activity on climate, forests, soil and water to the Agricultural Society of Rutland County, Vermont. Marsh's acclaimed speech later was published in 1848.
Marsh developed his human impacts material further for his seminal book Man and Nature; or, Physical Geography as Modified by Human Action 1864. Marsh's book, still in print, is a foundational work of the conservation movement and presaged modern environmental science.
*"Prophet of Conservation" is the title of David Lowenthal's 2000 biography, George Perkins Marsh: Prophet of Conservation. Seattle: University of Washington Press.