Career
Karsch became an Esperantist in 1908 and was soon secretary of a local group of the German Esperanto Association 1910-1914, serving as its president from 1924 on. In 1928 he became komisionano and vice-president of the UEA. Then, when Eduard Stettler was president, Karsch often stood in for Stettler, who was in ill health. At the 1934 Stockholm World Esperanto Congress Karsch was not reelected to the Komitato.
In protest, President Stettler resigned.
Karsch stayed in contact with the Swiss leadership of the UEA but became inactive (largely because of the Hitler regime) and did not participate in the Geneva UEA of 1936.