CLIMATE SCIENTISTS WOULD prefer to have all climate change information recorded by weather instruments, but suitable instrumentation was practically nonexistent before the 19th century. As a result, investigators of longer-term (paleoclimatic) climate changes rely on datable noninstrumental information. Climate scientists refer to noninstrumental records as proxy records, because they are substitutes for direct measurements taken by instruments. There are four principle proxy record sources: human/historical, glaciological, geological, and biological. The timespan and level of detailed information among the sources vary, but getting the right climate change signal is important, because proxy data play a central role in developing accurate climate prediction models.

Human (or historical) proxy evidence for climate change is taken from a diversity of sources, ranging from clues in prehistoric cave paintings, to remarks ...