Chapter 3 - Ground Temperature Histories: Evidence of Changing Climate

Abstract

All ground surface temperature (GST) histories can be divided into three main groups—(1) embracing the Holocene (0.01 Ma) or so, (2) one or two millennia, and (3) the recent 100–200 years—according to their temporal length. The first time interval is described with respect to the deep boreholes. The chapter presents the summary of the 1000–2000 years' long GST temperature record as well as of the evidence of the recent warming. Most of existing boreholes are generally 500–600 m deep and thus contain information only about approximately the past 500 years. GST history from 1500 to the present is thus especially of interest, because these data represent the bulk of available GST reconstructions. The earlier GST histories were evaluated from the inversion of the temperature logs measured in a suite of boreholes from Ontario Province of Canada. Only deep boreholes were used for these GST inversions; thus, calculated GST histories were at least 1000 years long. The GST reconstructions from relatively shallow boreholes may serve as a valuable estimate of the recent climate changes in the specific regions at the climatic map.