Global Borehole Temperature Database for Climate Reconstruction: readme file ----------------------------------------------------------------------- World Data Center Paleoclimatology ----------------------------------------------------------------------- NOTE: PLEASE CITE ORIGINAL REFERENCES WHEN USING THIS DATA!!!!! CONTRIBUTORS: Pollack, H.N. and Huang, S., University of Michigan NAME OF DATA SET: Global Borehole Temperature Database for Climate Reconstruction LAST UPDATE: November 2016 (filenames huang2016*.txt) IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 1998-044 SUGGESTED DATA CITATION: Huang, S. and Pollack, H.N., 1998, Global Borehole Temperature Database for Climate Reconstruction. IGBP PAGES/World Data Center-A for Paleoclimatology Data Contribution Series #1998-044. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCES: Huang, S., Pollack, H. N., and Shen, P.Y., 2000. Temperature trends over the past five centuries reconstructed from borehole temperatures. Nature, 403: 756-758. Pollack, H.N., Huang, S., and Shen, P.Y., 1998. Climate Change Record in Subsurface Temperatures A Global Perspective. Science, 282 279-281 Huang, S., Pollack, H. N., and Shen, P.Y., 1997. Late Quaterary temperature change seen in world-wide continental heat flow measurements. Geophys. Res. Lett., 24 1947-1950 GEOGRAPHIC REGION: Global PERIOD OF RECORD: Late Quaterary LIST OF FILES: readme.borehole.txt (this file), 1012 huang2016*.txt files (latest version), 952 huang2013*.txt files (2013 version) DESCRIPTION: Global Database of Borehole Temperatures and Climate Reconstructions This project has as its goal the design, assembly, analysis and interpretation of geothermal observations on continents relevant to understanding the nature and causes of climate change over the past five centuries. The project was inititated by the Geothermal Laboratory of the University of Michigan, USA. Important collaborations have been developed with the Geophysical Institute of the Czech Academy of Sciences, and with a working group of the International Heat Flow Commission of IASPEI. Funding for this project has come from the U.S. National Science Foundation, the U.S. National Oceanic and Atmosphereic Administration, and the Czech - U.S. Science and Technology Program. The principal components of the database are Basic geothermal observations from field surveys and laboratory measurements, principally comprising borehole temperature logs and thermophysical properties. This section includes data only from boreholes at least 200 m deep. The data listed are restricted to the range 20-600 meters. Data above 20 m have been omitted because they include annual variability, and data below 600 m have not been included because they contain no information about the past 500 years. Quality control measures have occasionally required the deletion of other data within the 20-600 m range. A five-century ground surface temperature history derived for each site by a standardized inversion procedure operating on the basic observations. The derived history is presented as century-long temperature trends for each of the past five centuries. This representation emphasizes longer term variations of the climate history, and thus is complementary to high resolution proxies such as tree rings, ice cores, corals and lake sediments. The name of the person who can be contacted to learn more about the data and the site. This is either the name of the original investigator who made the observations, or the name of a regional or national data compiler. Some data remain proprietary, and therefore are not accessible directly from this database. Database users desiring access to these data should request the data directly from the person listed as the data contact. A list of investigators engaged in climate studies involving geothermal data can be found at the original web site of this database at the University of Michigan, located at http://www.geo.lsa.umich.edu/~climate. Brief Introduction to the Geothermal Approach of Climate Reconstruction One of the most important components of climate change is the variation of temperature at the Earth's surface. Because temperature changes at the surface affect the distribution of temperature in the subsurface, ground temperatures comprise an archive of signal of past climate. How Can Borehole Temperatures Be Related to Climate Changes Thermal regime at shallow depths of the crust is controlled by the temperature condition at the surface and the heat flowing from deeper part of the Earth. In an idealized homogeneous crust, if the surface temperature is steady, the distribution of ground temperature is a linear function of depth. However, if the surface temperature changes with time, the ground temperature will depart from the linear distribution which is governed by heat flow (q) and thermal conductivity (k). A progressive cooling at the surface will cool down the rocks near to the surface, increase the thermal gradient at shallow depths, and lead to a temperature profile with curvature like the one shown in green in the illustration above. A progressive warming, on the other hand should be responsible for a temperature profile with smaller even negative thermal gradients at shallower depths like the one shown in red. If the surface temperature oscillates with time, oscillations in the ground temperature will follow. The magnitude of the departure of ground temperature from its undisturbed steady state is related to the amplitude of the surface temperature variation, and the depth to which disturbances to the steady state temperature can be measured is related to the timing of the original temperature change at the surface. A ground surface temperature history is therefore recorded in the subsurface. By careful analysis of the variation of temperature with depth, one can reconstruct the past fluctuation at the Earth's surface. Advantages of the Geothermal Approach in Climate Studies Direct Temperature Study It is a kind of direct temperature - temperature study. Therefore, it is free of any uncertainties due to conversion from proxy data to temperatures. Important Time Interval The time interval over which the geothermal technique has resolving power covers both industrial and pre-industrial periods. Fewer Anthropogenic Disturbances There exist many ground temperature profiles measured from boreholes located in remote areas. Climate information preserved in those temperature profiles contain fewer anthropogenic disturbances such as urban thermal island effect and agriculture. Extensive Geographical Coverage There exist tens of thousands of borehole in the world which have been systematically temperature logged for heat flow determination. The huge archive of existing borehole temperatures comprises a great potential for a comprehensive world wide paleoclimate study.