In the 1860's and 1970's, in the United States, there was a great post-war westward migration. Many settlers began to try to farm lands west of the 100th meridian. These normally very arid regions experienced a couple of decades of much greater rainfall during this period. We know today that this was merely a cyclical variation of the type that is constantly occurring in the climate. However, people of this time chose to believe that this was a permanent change, attributing the shift in rainfall to anthropogenic effects (any of this sound familiar?) The saying at the time was that "rain followed the plow."
The basic premise of the theory was that human habitation and agriculture through homesteading affected a permanent change in the climate of arid and semi-arid regions, making these regions more humid. The theory was widely promoted in the 1870s as a justification for the settlement of the Great Plains, a region previously known as the "Great American Desert". It was also used to justify the expansion of wheatgrowing on marginal land in South Australia during the same period.
According to the theory, increased human settlement in the region and cultivation of soil would result in an increased rainfall over time, rendering the land more fertile and lush as the population increased. As later historical records of rainfall indicated, the theory was based on faulty evidence arising from brief climatological fluctuations. The theory was later refuted by climatologists and is regarded as a serious error. In South Australia, George Goyder warned as early as 1865, in his famous report on farming in the state, that rain would not follow the plow. Despite this, until further droughts in the 1880s, farmers talked of cultivating cereal crops up to the Northern Territory border. Today, however, grain crops do not grow further north than Quorn.
The result was eventually disaster for thousands and many abandoned farms in places like Eastern Colorado. To some extent, the theory had a grain of truth - changes in land use do affect the climate. For example, the loss of snow on Kilimanjaro is generally attributed (by non Al Gore types) to deforestation in the area. But as is so often the case, the effects of man's land use tended to be more local (as with urban heat islands in cities) rather than regional, and ended up in this case being small compared to natural variations.