Article in German, Abstracts in English and German.The perception that regional climate might be influenced by deforestation started early in Europe. The first to consider human influence on regional temperature and air quality was Theophrastus (372-288 AD). He started a discourse that intensified when Europeans discovered and colonized America, peaked at the end of the 19th century and then fell into oblivion at the beginning of the 20th century. In his case study on the Valencia Lake in Venezuela (1799) Alexander von Humboldt laid the scientific foundations to systematically examine the question whether changes in climate could be human induced. The follow-up studies undertaken by Jean Baptist Boussingault on the same lake and on others in Latin America caused a sensation world-wide and his arguments were taken up by the early environmental movement (e.g. George Marsh) in defence of forests in Europe, the U.S. and in the colonies. The positive influence on climate ascribed to forests reached mythical dimention, leading to extensive reforestation programs to increase rainfall in areas with low precipitation. When these programs failed, the fear that the destruction of forests could lead to human induced climatic catastrophes was generally discredited.