Reconstructing the Climates of the Past
Human nature, it seems, has caused people to explore the story of our past ever since the dawn of time, whether it has been the history of nations, that of civilizations, or that of our planet and solar system. The history of past climates is no exception. This need of memory has become even more crucial over the last few decades, as an understanding of the climate and its evolution has become of major concern for the near future of our civilization.
To aid us in this task, we have meteorological measurements, which we’ve had for around a century. More recently we’ve been able to use observations from space. On the other hand, glacial archives, marine and lake sediments, fossil fauna and flora, soil, trees, limestone formations, and coral, have preserved a record of the past. When dated, these sources enable us to explore the past and to reconstruct continuously certain phenomena that, depending on the situation, describe the seasons, centuries, and millennia of the climate, of our atmosphere, of the oceans, and of the continents. The information thus archived requires a great deal of deciphering, in a certain sense analogous to the task of Jean-François Champollion in the nineteenth century when he unraveled Egyptian hieroglyphs. The climates of the past are the subject of a distinct scientific discipline: paleoclimatology.
The guiding principle of paleoclimatology rests on a simple idea: many characteristics of what exists on Earth, whether in the living world, in the mineral world, or in the water cycle, depend on the climatic conditions that existed when the different elements were formed. If these diverse materials accumulated layer by layer in such a way that the sequence of time of the deposits has been preserved, at least for the most part, we have then a climatic archive that can be used, provided that it is physically accessible, that it can be dated, and that some of its properties can grant us access to information that enriches our understanding of the climates of the past. The methods that