Environmental Engineering Reference
In-Depth Information
Figure 9.1
Idealized examples of changes in climatic records.
EVIDENCE FOR CLIMATIC CHANGE
PROXY INDICATORS
There are a number of different types of evidence that can be used to decipher what
climatic conditions have prevailed in the past. The best is where we have records of
instrumental observations at a particular site. In this case we will know on what date what
weather elements were observed. In the early stages of instrumental use, neither the
instruments nor their siting were standardized, so it is difficult to compare the values
between sites. Instrumental records can take us back to the seventeenth century in a few
parts of the world. Prior to the instrumental era, many weather observations were made in
documents. Sometimes these were weather diaries, usually noting when the weather was
extreme and sometimes more general observations. Other documentary examples come
from reports on agriculture, ships' logs, grain price records and wine harvest times. In
these cases we normally know the date or period referred to though the information is
qualitative. We may hear only that the year was dry or wet but cannot tell precisely how
dry or wet. Judgement on behalf of the observer may also be significant.
Prior to these written records we have to depend upon
proxy
records, which are any
types of evidence that provide indirect measures of former climates. We can divide these
proxy records into three major categories - geomorphological, lithological and biological.
Each type contains a large number of different lines of evidence and we can only
introduce the subject in this chapter. Anyone wanting more detailed information should
consult the topics listed at the end of the chapter.
