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Borehole Temperatures
The IHFC
global data base for borehole temperatures
and climate reconstructions (http://www.geo.lsa.umich.edu/climate/)
is currently located under the custody of
Shaopeng Huang at the University of
Wisconsin. 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. Currently,
the global database of borehole temperature
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 (http://www.ncdc.noaa.gov/paleo/borehole/borehole.html) and
at the University of Michigan
http://www.geo.lsa.umich.edu/~climate).
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.
Activities 2007 - 2009
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.
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