Slogan : Historical climate records tell various stories — Let's test them all.
We'd like to understand the climate changes since 800 AD (i.e., for just over a millennium). In addition to the post-industrial era, this period includes so-called Medieval Warm Period (~900-1300 AD) and Little Ice Age (~1300-1900AD) (see e.g.
Medieval Warm Period on wikipedia). The anomalously warm and cold periods are probably caused by the variation of volcanic & solar activities, land use changes and perhaps the change of oceanic circulation pattern, but the contribution of each component is not well understood.
In addition to satisfy the scientific and historical curiosity, this experiment is driven by the
urgent need to refine the climate predictions. The climate models have so far been evolved to simulate the recent climate. The last "millennium" can provide an extra constraint to refine the models further.
However, both the driving force and the climate reconstructions over the pre-industrial era are based on the analysis of the natural archives of climate sensitive quantities, such as the growth of trees and seashells, and the changes of chemical, biological, and isotopic compositions in lake sediments and ice core samples. These "proxy" data are truly useful only when we fully explore the enormous range of the combined uncertainty.
