HISTORICAL RECORDS OF climate data include the instrumental record and proxy climate data from human recorded history. Proxy records are a substitute for direct measurements by meteorological [Page 232]instruments. The principal sources of historical proxy records are written, archaeological, and iconographie evidence.

Accurate reconstruction of past climate relies on information from instruments that measure air pressure, wind speed, wind direction, precipitation, air temperature, and humidity made at weather or climate stations around the globe. But looking further back in time, the record declines, both in terms of the area of the world covered and the number of variables measured. By the late 1700s, it includes only a handful of places, mainly in Europe.

The time period covered is not the only consideration. The data must also be ...