To appreciate the risks of runaway climate change, it is necessary to understand its science. We have therefore summarised key aspects which we aim to cover in our future multimedia output. These won't explain everything, but they will help a diverse global audience understand why we can no longer afford to ignore climate change..
What scientists knew when about greenhouse gases and temperature:
|In 1824, the French scientist, Joseph Fourier, discovered that Earth's atmosphere behaved like a greenhouse, absorbing and retaining more heat than predicted in a vacuum.||In the 1860's John Tyndall investigated the absorption of infrared in different gases and discovered that some gases, notably water vapour, methane and carbon dioxide strongly blocked radiated heat. In his words, they act as a "blanket more necessary to the vegetable life of England than clothing is to man".|
|In 1896 the Swedish scientist, Svante Arrhenius realised that the CO2 added to the atmosphere through burning fossil fuels would raise average temperatures. He calculated that a doubling of the concentration of CO2 in the atmosphere would cause temperatures to rise by 5˙C.||In 1938, a British engineer, Guy Callender, presented evidence that the temperature and concentration of CO2 in the atmosphere had risen over the previous half century and that spectroscopic measurements showed that CO2 in the atmosphere was effective in absorbing infrared. Few scientists took his ideas seriously at the time.
Twenty years later in 1958, Charles Keeling started regular measurements of atmospheric CO2 levels at Mauna Loy Observatory in Hawaii. These provided the first evidence that concentrations were rising - from 315 ppm in 1958 to 391ppm in September 2012. The seasonal fluctuations reflect CO2 released by trees in the northern hemisphere during the summer. CO2 concentrations are now measured in 100 locations worldwide.
In the early 1970's some scientists believed the Earth would enter a cooling period due to lower sunspot activity, but in 1979, a report by the United States National Research Council confirmed that doubling the concentration of CO2 in the atmosphere would lead to surface warming between 2˙C and 3.5˙C, with greater increases in high latitudes. These predictions are now proving to be accurate.