The Climate and Greenhouse Gases
Through the eyes of glaciologists we have led you to the discovery of our white planet, of the world of ice with such variable shapes and with such a rich memory. What will become of this ice on a planet whose climatic history is no longer written by Mother Nature but quite probably is already influenced by the activities of humans and which will probably be even more so in the decades and centuries to come? This question, which bears on the role of human activities in the warming we have been experiencing for a few decades and on the evolution of our climate from now until the end of the century and beyond, is the focus of the next several chapters. But let’s first go back to the greenhouse effect, to its role in the climatic machine, and to its evolution during the last centuries in response to human activity.
To explain the greenhouse effect we must look at it as climatologists, which will enable us to say a bit more about the functioning of our climate, of which the Sun is the initial driving force. For even if the Earth absorbs only a small part of the energy the Sun emits, that energy is much greater (around 7,000 times) than the geothermal flux that comes from inside the Earth. That flux thus has no notable influence on the average climate of our planet.
In a given place, the solar energy received at the top of the atmosphere— insolation—is extremely variable. It follows the rhythm of the succession of days and nights, which is connected to the rotation of the Earth on its axis, and of that of the seasons, which result from the obliquity, the tilt of that axis in relation to the plane of the Earth’s orbit. It also depends on the average incline of the Sun’s rays and thus on latitude. The result of these diurnal,