The nineteenth century saw a remarkable development of our knowledge about past climatic variation. The French natural philosopher Joseph Fourier (1824) put forward the idea that the climate on earth was determined by the heat balance between incoming solar radiation (‘light heat’) and outgoing radiation (‘dark heat’) and this idea was further pursued by Claude Pouillet (1837). They both realised that the atmosphere might serve as an absorbing layer for the outgoing radiation to space and that the temperature at the earth's surface might therefore be significantly higher than would otherwise be the case.

At about the same time the Swiss ‘naturalist’, Louis Agassiz (1840) suggested that features in the countryside, such as misplaced boulders, grooved and polished rocks, etc., were indications of glacial movements and that major parts of central Europe, perhaps even northerly latitudes in general, had been glaciated. This revolutionary idea was, of course, not readily accepted by his colleagues, but it stimulated others to search for further evidence. Agassiz's idea found acceptance during the following decades, not least because of his studies in the Great Lakes area in the USA.

The idea that the atmosphere plays an important role in determining the prevailing climate of the earth was further developed in England by John Tyndall (1865). He actually measured the heat absorption of gases, including carbon dioxide and water vapour, and emphasised their importance for the maintenance of the prevailing climate on earth.