Listening to climate sceptics, it is easy to think the entire science of global warming hinges on the wording of a few emails sent from a university department. But with the Copenhagen conference under way, it is worth noting that climate science, or more specifically the influence of carbon dioxide on the natural greenhouse effect of the Earth, has a long and illustrious history.
It started 200 years ago with the work of Joseph Fourier, a French mathematician who in 1820 was the first to realise the heat-trapping potential of the atmosphere. Sunlight penetrates the atmosphere to heat the Earth's surface. Heat is re-radiated in the form of infra-red radiation, which is more easily trapped by the atmosphere on its outward journey to space.
In 1859, John Tyndall, a natural philosopher, demonstrated that carbon dioxide and water vapour were the most important heat-trapping molecules in the atmosphere. It was the atmosphere's ability to trap heat that made Earth habitable when compared with, say, Mars, which has a very thin atmosphere.
However, it was not until 1896 that Svante Arrhenius, a Swedish scientist, named the phenomenon the "greenhouse effect" using a rather inaccurate analogy. Like many experts interested in this field, Arrhenius was concerned about what caused the previous ice ages and he was not too concerned about the chances of rising CO2 leading to higher temperatures.
Nevertheless, using very basic equations, Arrhenius calculated that doubling the CO2 content of the atmosphere could lead to a rise in temperature of 5C or 6C – a remarkably accurate forecast given the rudimentary knowledge at the time. He also thought it would take thousands of years to reach this level, which he did not see as a problem because he failed to anticipate the exponential increase in the rate of man-made CO2 emissions.
Steaming ahead of the rest
The unsung hero of the science of global warming, however, is Guy Stewart Callendar – an English scientist and amateur meteorologist. In 1938, he read old temperature measurements and found these had risen from the 19th-century onwards. He found a similar trend with CO2 concentrations in the atmosphere and suggested this could account for the temperature rise. Callendar was interested in what caused the last ice age and worried about the prospect of another. Although he couldn't prove global warming was under way, he certainly provided some good evidence to suggest that it was a real possibility.
The man who blazed a trail
During the 1950s, US scientists demonstrated with a series of annual measurements how CO2 was rising. At the time, many still believed this had no influence on the greenhouse effect, but Callendar wrote a paper in 1958 insisting that a rise in anthropogenic CO2 could lead to a rise in global temperatures. Fifty years later, the science is largely settled, despite what sceptics say.