Extreme climates and current analogues : Little Ice Age and Medieval Optimum

It is imperative to place the warming of the last century in a broader temporal context in order to determine its singularity and distinguish the underlying causes, both natural and anthropogenic. Climate variations never repeat themselves identically, but the same physical, chemical and biological mechanisms are at work, and can be simulated numerically using the same models used to forecast possible futures. The climate of the last millennium can therefore be used to test multiple hypotheses, with record reliability and spatial coverage that are generally sufficient. Studying this period also enables us to consider the impact of climate on human societies and to study their reactions. These lessons from history can help us to make the right choices today, even if our globalized society is obviously very different because of its demographics and global connectivity.