Temperatures beneath the Earth's surface consist of two principal components: a steady-state component related to the flow of heat outward from the deeper interior, and a downward-propagating transient component related to the perturbations from changes at the ground surface. The recent effort among the geothermal community in reconstructing a ground surface temperature history from borehole temperature data adds a new dimension to the study of global climate change. It is widely recognized among the scientific community that the independent climate information comprised in borehole temperatures is complementary to instrumental records and other conventional climate proxies. With the support from the international heat flow community, a global database of borehole temperatures has been constructed for climate research.
The IHFC global data base for borehole temperatures and climate reconstructions is currently located under the custody of Shaopeng Huang at the University of Wisconsin and consists of more than 950 boreholes in North America, South America, Europe, Africa, Asia, and Australia. The database is accessible to the scientific community both at the World Data Center-A/NOAA Paleoclimatology Program at the National Climatic Data Center (https://www.ncdc.noaa.gov/data-access/paleoclimatology-data/datasets/borehole) and at the University of Michigan http://geothermal.earth.lsa.umich.edu/). The significances of this database and the results derived from borehole temperatures are highlighted in the Report of the US National Research Council of the National Academies on 'Surface Temperature Reconstructions for the last 2000 Years' (National Research Council, 2006) and the IPCC Report 2007. The IHFC and the custodian of this database, Shaopeng Huang of the University of Michigan, thank all contributors of data and acknowledge supports from NOAA Grant NA07OAR4310059 and NSF Grant ATM-0317572.
Suggested citations for this database are:
Reconstructing past climate provides a useful context for the discussion on the twentieth century global warming and future climate changes. In their recent paper published in the Geophysical Research Letters, Shaopeng Huang and Henry Pollack of the University of Michigan and Po-Yu Shen of the University of Western Ontario present a suite of 20,000 year reconstructions that integrate three types of geothermal information: a global database of terrestrial heat flux measurements, another database of temperature versus depth observations, and instrumental record of temperature. These reconstructions show the warming from the last glacial maximum, the occurrence of a mid-Holocene warm episode, a Medieval Warm Period (MWP), a Little Ice Age (LIA), and the rapid warming of the 20th century. The reconstructions show the temperatures of the mid-Holocene warm episode some 1-2 K above the reference level, the maximum of the MWP at or slightly below the reference level, the minimum of the LIA about 1 K below the reference level, and end-of-20th century temperatures about 0.5 K above the reference level. Huang was invited to participate in the Workshop on Bayesian Hierarchical Models for High-Resolution Climate Reconstructions organized by Casper Amman at the National Center for Atmospheric Research in Boulder, CO, USA. Two other IHFC members invited to this workshop were David Chapman of the University of Utah and Robert Harris of Oregon State University.
As another focus of the working group "Paleoclimate" session CL35 "Subsurface temperature signals of climate change, processes involved, and importance to climate modeling" was organized as part of the section "Climate: Past, Present, Future" of the General Assembly of the European Geosciences Union in Vienna in April 2008 by V. Rath, J. Gonzales-Rouco and IHFC member J. Safanda. Altogether 30 contributions (11 oral contributions including 4 solicited ones and 19 posters) addressed different aspects of the surface temperature history reconstruction from the present subsurface temperature profiles. The conveners of the session have agreed on organization of such a session every second year, which means that the next meeting of this kind should be convened in the spring of 2010.