Have Humans Already Changed the Climate?
In 1896 Svante Arrhenius brought attention to the fact that humans were in the process of changing the amount of carbon dioxide in the atmosphere and that as a consequence our planet would warm up by 5°C from that point to the end of the twentieth century, according to his estimates. It was only eighty years later that this risk of warming and its potential consequences were taken seriously. This awareness quickly led to the establishment of the Intergovernmental Panel on Climate Change (IPCC) in 1988, which in 2007 concluded that our activities are very likely at the origin of a marked warming that we have been experiencing since the mid-twentieth century.
Until the 1970s very few research teams were looking at the impact of human activity on the climate. It is true that after an initial period of warming up to the beginning of the 1940s, temperatures stabilized, then slightly decreased. Moreover, in 1975 Willi Dansgaard,1 the Danish glaciologist, a pioneer in the reconstruction of past climates from the ice of Greenland, extrapolated one of the climatic records he had obtained at Camp Century northwest of that ice cap and predicted a future cooling of the planet. The idea at that time was that the length of the interglacial period in which we are living, the Holocene, would end quickly. That fear was in fact unfounded since the Earth’s orbit is such that a return to a glacial period is not anticipated for another 10,000 years or even more. But thirty years ago, we were far from the cry of alarm that we are sounding today regarding the effect of human activity on the climate.
A few pioneers did, however, attempt to have their voices heard. In the 1930s Guy Callendar, who had correctly seen an increase in CO2 in the atmosphere, sought to establish a connection between the warming that had