A Brief History of Climate Change

In lay terms, sunlight passes through the atmosphere easily but when it is absorbed by the Earth’s surface and released as heat (infrared radiation), a different form of energy, the atmosphere acts as a barrier to its escape back into space. This atmospheric blanketing effect then results in elevated surface temperatures. Whilst this theory was oversimplified, it is often cited as the first reference to a natural “greenhouse effect”. We now know that the atmosphere does not behave in this way but it took a community of physicists to identify the atmospheric constituents and processes that lead to planetary warming.

Claude Pouillet and Samuel Langley’s contributions on measuring solar radiation and how it permeates through space were invaluable to this pursuit, but it was not until 1859 that John Tyndall showed that water vapour (H2O), carbon dioxide (CO2) and ozone (O3) were the atmospheric gases responsible for limiting heat escape. Although they were present in small quantities, they had especially effective heat-trapping potential, with water vapour having the greatest potency. The major atmospheric constituents—nitrogen (N2) and oxygen (O2)—in contrast, were almost transparent to radiation. He concluded, “without water vapour [in the atmosphere], the Earth’s surface would be held fast in the iron grip of frost”. That is, water vapour which makes up 0-4 per cent of the atmosphere (depending on location and season) was most essential in maintaining elevated global temperatures. These compounds that have the ability to absorb (and emit) solar radiation are now referred to as greenhouse gases (GHGs).

While experts had established the heat-trapping properties, it was not until 1896, and by Svante Arrhenius, that the planetary warming that GHGs could effect was quantified. Building on the works of Fourier and Tyndall, Arrhenius predicted that should the quantity of CO2 (then, carbonic acid) in the atmosphere be doubled, terrestrial temperatures would rise by 5-6°C. Consequently, the combustion of coal, a major source of CO2 and the primary fuel source of the time, could cause a change in climatic conditions. He, however, thought that this change in climatic conditions would take thousands of years to manifest and would be a positive for the environment by delaying the next ice age.