The Swedish scientist Svante August Arrhenius (1859–1927), who was one of the founders of the discipline of physical chemistry, is sometimes credited as the first person to discuss in detail the effects of carbon dioxide (CO2) on Earth’s climate. Arrhenius came upon his theory while studying past ice ages, and in 1896 published a paper in which he proposed that ice ages occur when CO2 levels go down. By his estimates, doubling CO2 amounts would increase average world temperatures by about 2.5°F (5°C) and halving the levels of this gas would have the opposite effect. Recent modeling studies come quite close to Arrhenius’s original estimate. Unlike today’s environmentalists and climatologists, however, the Swedish scientist believed that global warming would be a good thing for two reasons: it would help prevent another ice age and it would aid in crop production to feed a hungry world.