ABSTRACT

In 1796, Scottish physicist John Leslie visited the Swiss Alps seeking evidence in support of his theory that the entire Earth is slowly warming through the accumulation of absorbed solar radiation. He observed that parallel ridges of loose angular stones (moraines) become increasingly vegetated with distance from the margins of active glaciers, and he inferred the secular retreat of glacier margins by at least 3000 vertical feet. Leslie anticipated by four decades the discovery of a former Ice Age by geologists and, while his theory of climate change was faulty in being unaware of Earth's outgoing non-luminous (infra-red) radiation, his inference regarding glacial recession was robust. If not due to topographic lowering of the Alps, it was inexplicable to nineteenth century climate physics in the absence of an unexplained change in radiative forcing.