Climate : Past, Present and Future

Orateur : Marie-Antoinette MÉLIÈRES (LTHE, University of Grenoble)

This talk will concentrate on two questions. The Earth’s climate has been changing incessantly throughout the ages. Why ? The warming that is likely to take place in the course of the 21st century has caused the scientific community to sound the alarm. Why ? In answer to these two questions a brief outline will be given of how the present climate on Earth can be described in terms of energy, and of the principal causes of climate change. The example of the large glacial oscillations of the last few million years, and the small fluctuations of the last millennia, puts the origin of the recent warming into context, as well as its consequences for the physical and biological world. As human activity continues to emit greenhouse gases, the climate of 2100 will depend on the scenario adopted. If an average warming by 2ºC (low scenario) of the Earth’s surface could be “manageable”, at the cost of adapting, it is not the case for 5ºC (high scenario). That would return us to a climate that prevailed more than 10 million years ago, before the species homo existed, and would be very different from the climates to which our ecosystems have adapted over the last few million years. It is, for example, profoundly doubtful that the planet would be able to feed ten billion inhabitants.

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