An introduction to climate change - Climate Change: Biological and Human Aspects - page 5

Indeed, he contemplated that a reduction in greenhouse gases might throw the Earth
into another ice age. Strangely though, he never considered what might happen if
the concentration of greenhouse gases increased. Consequently, he never asked what
would happen if human action contributed additional greenhouse gases. In other
words, what would happen if there was the addition of an anthropogenic contribution
to the natural greenhouse effect?
It is this difference between the natural greenhouse effect and the additional human-
generated (anthropogenic) effect that is at the heart of the current issue of global
warming. The Swedish chemist and Nobel laureate Svante August Arrhenius first
proposed that the human addition of carbon dioxide to the atmosphere would result
in warming in 1896, although he himself did not use the term 'greenhouse', but
'hothouse'.
Fourier, Tyndall and Arrhenius are, today, rightly credited with providing the
initial grounding science for greenhouse theory. Yet it is often forgotten that in
the few decades following 1896 this theory was not high on many scientists' research
agendas, and indeed serious doubts arose as to the importance of the increase in
atmospheric carbon dioxide in changing the Earth's global climate. However, in
1938 a steam technologist working for the British Electrical and Allied Industries
Research Association, one Guy Stewart Callendar, managed to get a paper published
in the Quarterly Journal of the Royal Meteorological Society in which he noted that
humankind had added some 150 000 tons of carbon dioxide to the Earth's atmosphere
and that this, he calculated, would have warmed the atmosphere by some 0.003 ◦ C per
year. He also looked at (a limited number of ) meteorological records that suggested the
climate's temperature had increased at an average rate of 0.005 ◦ C per year (Callendar
refined this last estimate in 1961 using a larger meteorological data set). Callendar's
meteorological estimates and greenhouse warming calculation were well within the
right order of magnitude and his work, albeit limited, deserves to be remembered in
the history of climate change science.
Guy Callendar was not alone. At the end of August 1972 an atmospheric scientist,
J. S. Sawyer, estimated that the warming that might be expected with a continued
growth in fossil fuel emissions of carbon dioxide to 2000 would be 0.6 ◦ C. This was
quite prescient because less than half the total amount of carbon dioxide released into
the atmosphere between the Industrial Revolution and 2000 was in the atmosphere by
1970. In addition, as we shall see in Chapter 5, the United Nations (UN) Intergovern-
mental Panel on Climate Change (IPCC) consider that there was very roughly 1 ◦ Cof
warming from the beginning of the Industrial Revolution to 1990, so 0.6 ◦ C really is
not bad for about half the carbon dioxide. What is more, for a couple of decades up to
1970 the global temperature had actually been declining, making Sawyer's prediction
particularly brave as it seemingly went against the grain. So he was very close and,
with the benefit of hindsight, we can now see that between the 1970s and 2000 the
global temperature rose by close to 0.5 ◦ C!
Today the atmosphere is indeed changing, as August Arrhenius thought it might,
with the concentration of carbon dioxide increasing in recent times, largely due to
the burning of fossil fuels. In 1765, prior to the Industrial Revolution, the Earth's
atmosphere contained 280 parts per million by volume (ppmv) of carbon dioxide.
By 1990 (which is, as we shall see, a key policy date) it contained 354 parts per
million (ppm; either by mass or by volume) and was still rising. By 2005 (when this