Svante August Arrhenius (19 February 1859 – 2 October 1927) was a Nobel Prize-winning Swedish scientist who made discoveries in physics, chemistry and earth science.

Originally he was a physicist, but he won the 1903 Nobel Prize in Chemistry, and was a founder of physical chemistry.

Later in life, he turned to other scientific problems. He was the first person to predict that emissions of carbon dioxide, from the burning of fossil fuels, would cause global warming.

Early work 
His early work was on the conductivity of electrolytes. In 1884, based on this work, he submitted a 150-page essay on electrolytic conductivity to University of Uppsala for his doctorate. It did not impress the professors, and he received a low-class degree. Later, extensions of this work would earn him the Nobel Prize in Chemistry.

The most important idea in the thesis was his explanation that neither pure salts nor pure water is a conductor, but solutions of salts in water are.

Arrhenius' explanation was that in forming a solution, the salt splits up into charged particles (which Michael Faraday had given the name ions many years earlier). Faraday's belief had been that ions were produced in the process of electrolysis; Arrhenius' idea was that, even in the absence of an electric current, solutions of salts contained ions. He proposed that chemical reactions in solution were reactions between ions.

In an extension of his ionic scientific theory Arrhenius proposed definitions for acids and bases, in 1884. He believed that acids were substances which produce hydrogen ions in a solution and that bases were substances which produce hydroxide ions in a solution.

The Nobel Prize 
About 1900, Arrhenius became involved in setting up the Nobel Institutes and the Nobel Prizes. For the rest of his life, he would be a member of the Nobel Committee on Physics and a member of the Nobel Committee on Chemistry.

He used his positions to arrange prizes for his friends (Jacobus van't Hoff, Wilhelm Ostwald, Theodore Richards) and to attempt to deny them to his enemies (Paul Ehrlich, Walther Nernst). In 1903 he became the first Swedish persn to be awarded the Nobel Prize in Chemistry.

Later work 
After he had made his name, he turned to other scientific questions.

Physiology 
In 1904 he delivered (at the University of California) several lectures, to try and show the application of the methods of physical chemistry to the study of the theory of toxins and antitoxins, and which were published in 1907 under the title Immunochemistry.

Earth and planetary sciences 
He also turned his attention to geology (the origin of ice ages), astronomy, physical cosmology, and astrophysics, accounting for the birth of the solar system by interstellar collision.
He considered radiation pressure as accounting for comets, the solar corona, the aurora borealis, and zodiacal light.

He thought life might have been carried from planet to planet by the transport of spores. This idea is now known as panspermia.

Greenhouse effect
Arrhenius thought of a theory to explain the ice ages, and in 1896 he was the first scientist to think that changes in the levels of carbon dioxide in the atmosphere could make a big change to the surface temperature through the greenhouse effect. He was influenced by the work of others, including Joseph Fourier. Arrhenius used infrared observations of the moon to work out the absorption of infrared radiation by atmospheric CO2 and water vapour.
In its original form, Arrhenius' greenhouse law reads as follows:
"If the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetic progression".
This simplified expression is still used today:
ΔF = α ln(C/)

His book Worlds in the making (1908) was directed at a general audience. He suggested that the human emission of CO2 would be strong enough to stop the world from entering a new ice age, and that a warmer Earth would be needed to feed the rapidly increasing population:
 "To a certain extent the temperature of the earth's surface... is [related to] the atmosphere surrounding it, and particularly by the permeability of the latter for the rays of heat". (p46)
 "[The] theory has been styled the hot-house theory, because they thought that the atmosphere acted after the manner of the glass panes of hot-houses." (p51)
 "If the quantity of carbonic acid in the air should sink to one-half its present percentage, the temperature would fall by about 4°; a diminution to one-quarter would reduce the temperature by 8°. On the other hand, any doubling of the percentage of carbon dioxide in the air would raise the temperature of the earth's surface by 4°; and if the carbon dioxide were increased fourfold, the temperature would rise by 8°". (p53)
 "Although the sea, by absorbing carbonic acid, acts as a regulator of huge capacity, which takes up about five-sixths of the produced carbonic acid, we yet recognize that the slight percentage of carbonic acid in the atmosphere may by the advances of industry be changed to a noticeable degree in the course of a few centuries". (p54)
 "By the influence of the increasing carbonic acid in the atmosphere, we may hope to enjoy ages with more equable and better climates, especially as regards the colder regions of the earth, ages when the earth will bring forth much more abundant crops than at present, for the benefit of rapidly propagating mankind". (p63)

He was the first person to predict that emissions of carbon dioxide from the burning of fossil fuels and other combustion processes would cause global warming. Arrhenius clearly believed that a warmer world would be a positive change. Nevertheless, until about 1960, most scientists dismissed the greenhouse effect because they thought it was very unlikely to happen. Milutin Milankovitch had presented a mechanism for ice ages: it used cyclical changes in the orbit of the Earth (Milankovitch cycles). Nowadays, the accepted explanation is that orbital forcing sets the timing for ice ages with CO2 acting as amplifying feedback.

Human affairs 
He thought of the idea of a universal language (one language that would be spoken by everybody), proposing a modification of the English language.

Arrhenius was one of several leading Swedish scientists who helped create The State Institute for Racial Biology in 1922. This was a eugenics-influenced idea. It had originally been proposed as a Nobel Institute. Arrhenius was a member of the institute's board, as he had been in The Swedish Society for Racial Hygiene (Eugenics), founded in 1909.

References 

Nobel Prize in Chemistry winners
Swedish physicists
Swedish chemists
Foreign Members of the Royal Society
1859 births
1927 deaths