Borehole climatology: a discussion based on contributions from climate modeling

Abstract

Abstract. Progress in understanding climate variability through the last millennium leans on simulation and reconstruction efforts. Exercises blending both approaches present a great potential for answering questions relevant both for the simulation and reconstruction of past climate, and depend on the specific peculiarities of proxies and methods involved in climate reconstructions, as well as on the realism and limitations of model simulations. This paper explores research specifically related to paleoclimate modeling and borehole climatology as a branch of climate reconstruction that has contributed significantly to our knowledge of the low frequency climate evolution during the last five centuries.The text flows around three main issues that group most of the interaction between model and geothermal efforts: the use of models as a validation tool for borehole climate reconstructions; comparison of geothermal information and model simulations as a means of either model validation or inference about past climate; and implications of the degree of realism on simulating subsurface climate on estimations of future climate change.The use of multi-centennial simulations as a surrogate reality for past climate suggests that within the simplified reality of climate models, methods and assumptions in borehole reconstructions deliver a consistent picture of past climate evolution at long time scales. Comparison of model simulations and borehole profiles indicate that borehole temperatures are responding to past external forcing and that more realism in the development of the soil model components in climate models is desirable. Such an improved degree of Correspondence to: J. F. González-Rouco (fidelgr@fis.ucm.es) realism is important for the simulation of subsurface climate and air-ground interaction; results indicate it could also be crucial for simulating the adequate energy balance within climate change scenario experiments.

Impact of maximum borehole depths on inverted temperature histories in borehole paleoclimatology

“…The estimated changes in ground surface temperatures (GSTs) from borehole temperature inversions have been shown to agree well with surface air temperatures (SATs) during their period of overlap Huang et al, 2000;Harris and Chapman, 2001;Pollack and Smerdon, 2004). This agreement, when combined with results from modelling and observational studies of air and ground temperature coupling, has supported the assumption that multidecadal to centennial changes in SAT are coupled to equivalent changes in GST and, hence, motivate the interpretation of GST reconstructions as indicators of long-term changes in SATs (see Pollack and Huang, 2000;Bodri and Cermak, 2007;González-Rouco et al, 2009, for reviews and related references).…”

“…This will be complicated by significant losses in the number of boreholes available as the minimum depth criterion becomes deeper. For instance, Beltrami and Bourlon (2004) and González-Rouco et al (2009) (in Figs. 1 and 6, respectively), as well as Chapman and Davis (2010) estimate that only about 10 % of the boreholes in the global database extend to 600 m. These losses in data densities will therefore need to be property accounted for.…”

“…A large collection of work has inferred GST variations during the last five centuries to a millennium (Lewis, 1992;Huang et al, 2000;Beltrami and Harris, 2001;Pollack and Huang, 2000;Harris and Chapman, 2001;Beltrami, 2002;Beltrami and Bourlon, 2004;Pollack and Smerdon, 2004;Bodri and Cermak, 2007;González-Rouco et al, 2009) and estimated GST histories as long-term (centennial) trends that are generally consistent with meteorological and other paleoclimatic records (e.g. Pollack and Smerdon, 2004;Pollack et al, 2006).…”

“…Pollack and Smerdon, 2004;Pollack et al, 2006). Indeed, a wide range of research around the general subject of interpreting geothermal climate signals has developed over the last two decades (see Pollack and Huang, 2000;Bodri and Cermak, 2007;González-Rouco et al, 2009, for reviews and related references), including recent efforts to estimate heat storage in the terrestrial subsurface (Beltrami, 2001(Beltrami, , 2002Baker and Baker, 2002;Beltrami et al, 2002Beltrami et al, , 2006aHuang, 2006) and assessments of the long-term behaviour of GCMs and the suitability of their component soil models (Lynch-Stieglitz, 1994;Sun and Zhang, 2004;Smerdon and Stieglitz, 2006;Beltrami et al, 2006b;González-Rouco et al, 2003, 2006, 2009Stevens et al, 2007MacDougall et al, 2008MacDougall et al, , 2010Lawrence et al, 2008).…”

Estimating 750 years of temperature variations and uncertainties in the Pyrenees by tree-ring reconstructions and climate simulations

“…Currently, two main approaches are being used to advance this line of research: (1) creating new or extending the existing climate reconstructions back in time using documentary evidence or environmental proxies such as tree-ring parameters (width, density, isotopic content), corals, speleothems (Jones et al, 2009); and (2) simulations of natural and forced climate variability using climate models (e.g. Zorita et al, 2005;González-Rouco et al, 2009;Junglcaus et al, 2010).…”