The historical findings on climate change were an indirect consequence of research on another phenomenon such as geological history, causes of the ice age, carbon cycle and other agriculture, meteorological and purely scientific questions. In this article, we present these findings in the context relevant to climate change.
The story of the science of climate change started in 1824 when French physicist Joseph Fourier described that Earth’s atmosphere acts as a blanket that keeps it warm. He compared the Earth with the atmosphere to a box with a glass cover, similar to a greenhouse. We know that the main effect of the glass is to prevent the hot air inside to escape. Due to the use of the analogy, the process is known as the greenhouse effect.
In 1859, John Tyndal, an Irish physicist identified that CO2 and water vapor blocked the infrared radiation from escaping Earth’s atmosphere. In a laboratory experiment, he first found that coal-gas; a mixture of carbon monoxide, methane and other gases used for lighting was opaque to heat rays. He then extended the experiment to other gases in the atmosphere. (Source)
Swedish chemist Svante Arrhenius gave a strong hint on the impact of human-induced CO2 on Earth’s temperature in 1896. He calculated that doubling CO2 in the atmosphere can raise the temperature by 5-6 degree C. However he did not suggest the possibility of this in the future since the rate of coal burning was still much low.
An English engineer, Guy Stewart Callendar undertook a thorough and systematic effort to examine historical changes in Earth’s temperature. He took weather data from 147 weather stations around the world and initiated a massive international effort to standardize data from different countries and different years. After analyzing this data in detail, in 1938 he announced that the mean global temperature has risen by 0.5 degrees between 1890 and 1935, giving the first hint of global warming.
Gilbert Plass in his paper ‘The Carbon Dioxide Theory of Climatic Change’ in 1956 showed that doubling of CO2 concentration will cause the average surface temperature of the Earth to increases by 3.6° C given that other factors influencing the radiation balance remain same. He attributes the observed temperature rise to extra CO2 released due to industrial process and other human activities. The paper also discussed the possibility of the halving of CO2 concentration resulting in a temperature drop by 3.8 degrees.
Until now, the adverse impact of extra CO2 in the atmosphere was not a subject of concern for scientists. Scientists believed that the added gas in the atmosphere would be dissolved in the oceans. In 1955, Hans Seuss and Roger Revelle produced useful observations about the mixing of CO2 in oceans. They found that the life of a CO2 molecule in the atmosphere is of the order of 10 years before it dissolves in seawater. In his paper in 1957, “Carbon Dioxide Exchange between Atmosphere and Ocean and the Question of an Increase of Atmospheric CO2 during the Past Decades”, Revelle suggested the opportunity of studying the rates and mechanism of CO2 exchange between atmosphere and ocean.
Revelle and Suess hired Charles David Keeling to measure CO2 with precision. Keeling developed the measuring instruments and started measurements in 1958. Within two years of data from Antarctica, in 1960, he reported that the level of CO2 is rising in the atmosphere. The Antartica station was shut down due to lack of funds, but Keeling continued measurements at Mauna Loa, Hawaii. As the number of observations increased, the inexorable rise in Co2 concentration became evident. The jagged curve, popularly known as the Keeling curve is the most popular graphic evidence of the rising concentration of carbon dioxide in the atmosphere. The jagged curve is due to the seasonal variation in the concentration of CO2. The variation is explained by the absorption of CO2 by plants as they grow in spring and summer, and release it as they decay in autumn and winter.
A trend of falling temperature since 1940 was reported in 1961 by U.S. Weather Bureau’s Office of Climatology. This trend is seen in the graph from American Meteorological Society on annual temperature anomaly in degree C from 1946-60 mean. After the 1940s and until 1970s the average global temperature dropped. Several theories have been used to explain the cooling effect. Scientists have suggested that this could due to blocked sunlight by industrial pollution, enhanced by long-term climatic oscillations and changes in Earth’s orbits.
The warming trend resumed in 1975, and the scientific opinion started converging on global warming, not cooling.