engineer, Daniel Tilas, was studying the erratic boulders in many of the Scandinavian countries and the nations bordering the Baltic Sea, and he similarly speculated that they were brought to their present positions by glaciers that had existed in the past.35
Matters were about to change with the revolutionary ideas of James Hutton, a Scottish farmer turned naturalist. Hutton had lectured on the structure of the Earth, and in 1785 he presented his findings in a lecture to the Royal Society of Edinburgh. He argued that many rocks were not original, primeval structures, but had been modified and subject to sedimentation and later to weathering. Hutton introduced a basic principle of modern geology, somewhat clumsily termed uniformitarianism, which states that the natural forces that we see operating on the landscape today are essentially the same as those operated in past æons. He concluded that the movement of rocks by prehistoric glaciers, like the progressive erosion of the coast, was the cause of the landscape around us. Geology was suddenly seen as relevant to the study of the present-day Earth.
A replica of the original fossil from which the previous illustration was taken is on display in the Natural History Museum, London. The original specimen remains for the time being in the Muséum National d’Histoire Naturelle in Paris.
The term ‘geology’ had first been used by Ulisse Aldrovandi in his will of 1603, and came from the Greek γῆ (gē, earth) and λoγία (logia, study). Not until Hutton, however, was the subject given proper scrutiny and set on a firm scientific footing. Hutton used his principle of uniformitarianism to argue that many of the features of the present-day rocky landscape had begun at the bottom of the oceans, that many forms of rock had been produced by collections of ‘loose or incoherent materials’, and that these rocky layers were subject to rising, or falling, over the passage of immense periods of time. This was the first time anyone had put together the ideas fundamental to geology. In 1795, he finally published a book on his conclusions, and the new science of geology was firmly established.36
Several years after Hutton’s work, a Swiss hunter, Jean-Pierre Perraudin, decided to look further into the massive granite boulders that lay scattered around his home in the Alpine village of Lourtier. Perraudin was a professional hunter of chamois, the pretty mountain goats from which the finest leather is obtained. As he hiked across the mountains, he noticed two key facts: not only were there massive granite rocks scattered across the valley floor, but they were very different from the rocks nearby. They didn’t belong there. Secondly, he kept coming across deep longitudinal scratches and grooves carved into the valley sides. He sensibly concluded that this could mean only one thing – just as the villagers had always believed, glaciers had filled the valley in the past and had carried the boulders along, so it was these that had cut the deep grooves into the valley sides. Whenever an explanation for these curiosities had been sought in the past, philosophers said they were the evidence of the biblical flood, but Perraudin dismissed this as nonsense – he was certain that rising flood water could not move granite boulders. In 1815 he went to present his reasoned conclusions to Jean de Charpentier, born in Saxony and an enthusiast for geology, but Charpentier dismissed the idea as absurd. Undeterred, Perraudin raised the matter with a visiting engineer Ignaz Venetz, who lived in the nearby Rhône Valley, and the evidence he presented was so convincing that Venetz himself approached Charpentier and finally convinced him that the theory was right.37
Venetz worked further on the theory, and became convinced that – just as the hunter Perraudin had concluded – there had been eras in the past where glaciers had existed, and they had left indelible marks on the present-day landscape. He claimed that this proved that much of Europe had previously been covered with vast glaciers. At last it was becoming acceptable to say that the world’s climate truly had changed over time.38
Interest in this subject soon came to the attention of a physician and amateur geologist, Jean Louis Rodolphe Agassiz. He was born in 1807 in Môtier, in the French-speaking part of Switzerland, and qualified in Munich, Germany. He was soon to develop an interest in palæontology and he later studied in Paris under Georges Cuvier, who was greatly impressed by Agassiz’s growing knowledge of fossil fish. When Cuvier died, Agassiz saw himself as his natural successor, and later wrote an extensive work on fossil fish.39
As he developed his spare-time interests in natural history, Agassiz used to discuss his ideas with Karl Friedrich Schimper, a botanist turned poet and four years his senior. Schimper was a firm believer in the idea that prehistoric glaciation had created the landscape they saw around them, and he persuaded Agassiz that the views of Martel and, more recently, Perraudin, provided the evidence. Louis Agassiz devoted much of his free time to tracing changes in the Alps, monitoring snowfall and recording temperatures, and eventually he published an extensive monograph on glaciation. The title page of his book bears a vivid engraving of a glacier towering high above forest trees, and much of the contents comprises a comprehensive collection of detailed climatological tables.40
Agassiz owed his inspiration to Schimper, and to those who preceded him. Scholars have drawn attention to the way in which Agassiz not only failed to give them due credit, but sought actively to conceal it. In 1846, confident that his international reputation was assured, and that his mentors had been eclipsed, Agassiz emigrated to the U.S. and spent the rest of his life as a professor at Harvard.41
Since the revelations in the Alps that Pierre Martel documented more than 270 years ago, we have come to accept the occurrence of ice ages.
We have not always reached the right conclusions. Just 40 years ago, instead of the warmer world we are currently experiencing, people were heralding a new ice age by the end of the last millennium. Global cooling, not warming, was the threat that the public were warned about. Two of my friends wrote books prophesying an era of intense cold. In 1976 John Gribbin published Forecasts, Famines and Freezing and Nigel Calder wrote The Weather Machine and the Threat of Ice. Both confidently assured their readers that we were about to plunge into a new ice age and told how in the temperate latitudes we would need to retreat below the surface to create insulated, habitable cities in order to survive an icy future.42
Calder’s book followed a mammoth BBC television documentary in which he warned us that an ice age was imminent. However, a survey of all the scientific publications on climate in the 1970s shows that only 10 per cent upheld the idea of a new ice age. Even then, most academic opinion was beginning to point to the era we are now experiencing – a time of rising temperatures.43 Most papers were typified by one in Science in 1975, in which Wally Broecker coined the term ‘global warming’.44
This prediction can be traced back to the Swedish scientist Svante Arrhenius, who discovered the relationship between carbon dioxide in the air and the temperature of the atmosphere as long ago as 1896.45 Arrhenius followed this in 1908 with a book in which he suggested that we should expect a gradual warming of our world. He calculated that a doubling of the CO2 in the atmosphere would raise Earth’s average temperature by about 10°F (5–6°C) – an estimate still used by many researchers today.46
Between 1938 and 1957 a British engineer named Guy Callendar published a series of 26 papers that set out to relate the atmospheric increase in CO2 to rising temperatures. Then in 1953 Canadian physicist Gilbert Plass reviewed Callendar’s results and calculated that, if the concentration of atmospheric CO2 were to double, the global temperature would rise by about 7°F (3–4°C). This was a meticulous and important paper, but it was ignored by scientists. Plass was a professor at Texas A&M University when writing his paper and, because his university was regarded as undistinguished, his crucial conclusions were ignored. Academic snobbery drowned his prescient proposal.47
For those who want to see more of the way in which those pioneering investigations of climate change have matured into today’s concerns, the most authoritative book on the subject is the splendid volume Experimenting on a Small Planet by William Hay, Professor Emeritus
