Knut Johan Ångström (12 January 1857 – 4 March 1910) was a Swedish physicist.

[1] He focused his research work on investigating the radiation of heat from the sun,[2] terrestrial nocturnal emission and its absorption by the Earth's atmosphere,[3] and to that end devised various delicate[clarification needed] methods and instruments, including his electric compensation pyrheliometer,[4] invented in 1893, apparatus for obtaining a photographic representation of the infra-red spectrum (1895)[5] and pyrgeometer[6] (abt.

In 1900, Herr J. Koch, laboratory assistant to Knut Ångström, did not observe any appreciable change in the absorption of infrared radiation by decreasing the concentration of CO2 up to a third of the initial amount.

[7] This result, in addition to the observation made a couple of years before that the superposition of the water vapour absorption bands,[8] more abundant in the atmosphere, over those of CO2, convinced some geologists for a time that calculations by Svante Arrhenius for CO2 warming were wrong; though subsequent work in following decades eventually vindicated Arrhenius.

[9][10] The experiment, however, was careless seen from the current perspective with erroneous result[11] but of a historical significance in the development of the theory of the greenhouse effect amplified by CO2.