University of Utah Block U

Research Interests

The energy balance of the climate system has changed dramatically since pre-industrial times as a result of anthropogenic activities. These changes are obvious from observations of increases in global air and sea temperatures, as well as melting ice and rising global sea level (Intergovernmental Panel on Climate Change, 2013). The increases in temperature in the climate system have generally only been focused on the atmosphere, oceans, and cryosphere (e.g., Levitus et al., 2000; Levitus et al., 2001); however, the lithosphere is another important portion of the climate system that has received less work (Beltrami et al., 2002; Huang, 2006). One method for investigating the lithospheric response to climate change is the use of temperature-depth profiles measured in boreholes (Figure 1). The conductive temperature structure of the shallow continental crust reflects the superposition of the (1) steady-state background thermal regime that is governed by the outward flux of heat from the Earth and the (2) transient variations in ground surface temperature (GST). The steady-state thermal regime is mostly linear and varies on time-scales of millions of years while transient climatic signals are much shorter lived, it is possible to extract and interpret the record of GST variations in the past from the curvature that is imparted by the transient signal.

The geothermal community began to exploit the information found in the upper sections of temperature depth profiles from boreholes after the publication of the seminal paper by Lachenbruch and Marshall (1986). This paper related near surface perturbations in temperature-depth profiles measured in boreholes in Alaska to recent climate change. Reconstructions of surface air temperature (SAT) for the last 500 – 1000 years were subsequently generated from the GST histories from temperature-depth logs from boreholes by various workers (e.g., Huang et al., 2000; Harris and Chapman 2001; Beltrami, 2002). The geothermal method, as used in paleoclimate studies, has several strengths that are not evident in other methods of climate reconstruction. First, the geothermal method is a direct measure temperature, as opposed to an empirical calibration. Second, the temperature trends in boreholes are sensitive to long time periods (centuries) as opposed to short-term (seasonal) variations. Third, there is a broad coverage area over continental regions. However, there are shortcomings, owing to limitations from the physics of thermal diffusion. Particularly limiting is the progressive loss of high-frequency climatic information in the remote past (Clow, 1992).

In an attempt to exploit the strengths and understand the weaknesses of the geothermal method, geothermal studies of climate change have fallen into two categories. First, as mentioned previously, are those studies that seek to reconstruct SAT from GST over long time scales at the continental, hemispheric, or global scales (e.g., Huang et al., 2000; Harris and Chapman 2001; Beltrami, 2002). This type of study relies upon the assumption that ground temperatures reflect changes in air temperature. Therefore, the second study type are those that seek a more detailed understanding of the coupling SAT and GST. These investigations have primarily used meteorological stations collocated with pre-existing boreholes (Putnam and Chapman, 1996; Bartlett et al., 2006) or meteorological stations coupled with shallow boreholes or buried thermistors (e.g., Beltrami, 2001; Smerdon et al., 2003, 2004, 2006). It is at these localities that the processes and parameters that affect the coupling of SAT and GST, such as latent and sensible heat fluxes, precipitation, ground and vegetation roughness, and moisture content of the ground, are beginning to be understood. An additional item that is only beginning to be understood is the impact of land use change on GSTs (Lewis and Wang, 1998; Nitoui and Beltrami, 2005).

It is my belief that the geothermal method contains additional information that can be combined with other methods of studying climate change. However, the method (Figure 1) needs further study, and can be strengthened by attention to the following questions. What is the relationship between air and ground temperature over time scales appropriate to climate change studies? In particular, how well do changes in ground and air temperatures compare? What is the sensitivity of GST and its changes to climatic parameters such as solar radiation, precipitation, and snow cover? What is the long-term impact of changing snow cover on subsurface temperature? What are the significant factors impacting comparisons between geothermal data and SAT records? What affect is seen in different ecological regions?

To answer these questions, my research has been focused on the following areas:

  1. Operation and analysis of meteorological data and ground temperatures collected at the Emigrant Pass Observatory (EPO) (Davis and Chapman, 2012).
  2. Repeat logging of boreholes in northwestern Utah (Davis et al., 2010)
  3. An investigation of the ground thermal regime and land-atmosphere coupling across a climatic gradient in the Oregon Cascades using land surface models in collaboration with the EPA.

Future research directions and questions include, but are not limited to:

  1. Comparisons of individual boreholes with individual proxies. In particular, the comparison between a long proxy and a deep borehole, or, a small collection of both. Further, compare collections of deep boreholes and millennial length proxy temperature reconstructions (e.g., Chapman and Davis, 2010).
  2. Investigate changing climate conditions under different hydrological states (arid versus wet) and land cover (mature forest versus open/clear-cut) using both land based and satellite observations and land surface models. In particular, do the models reproduce the observations? Do on-site and satellite observations match or is spatial resolution a limiting factor? How does precipitation affect individual sites, and what is the effect of changing precipitation from snow to rain?


Figure 1. Basic aspects of the geothermal method of climate reconstruction. (a) An arbitrary time series of surface temperatures for the last century. Dashed line represents a climatic history with no temperature change. Triangles indicate times of borehole temperature logs illustrated in (b) and (c); log I in 1955, log II in 1975, and log III in 1998. The method asserts that changes in ground surface temperature are manifested as transient departures from the background, steady-state thermal regime. (b) Temperature-depth profiles for times I, II, and III. The linear profile results from the zero change scenario in (a) – dashed line. (c) Reduced temperature-depth profiles with background removed at times I, II, and III.

References

Bartlett, M.G., D.S. Chapman, and R.N. Harris (2006), A decade of ground-air temperature tracking at Emigrant Pass Observatory, Utah, J. Climate, 19, 3722 – 3731.

Beltrami, H. (2001), On the relationship between ground temperature histories and meteorological records: A report on the Pomquet station, Global and Planet. Change, 29, 327-348.

Beltrami, H. (2002), Climate from borehole data: Energy fluxes and temperatures since 1500, Geophys. Res. Lett., 29(23), 2111, doi:10.1029/2002GL015702.

Beltrami, H., J.E. Smerdon, H.N. Pollack, and S. Huang (2002), Continental heat gain in the global climate system, Geophys. Res. Lett., 29, 1187, doi:10.1029/2001GL014310.

Chapman, D.S., and M.G. Davis (2010), Climate Change: Past, Present, and Future; Eos, Transactions, of the American Geophysical Union, v. 91 (37), 325 – 326

Clow, G. (1992), Temporal resolution of surface-temperature histories inferred from borehole temperature measurements, Global Planet. Change, 98, 81-86.

Davis, M.G., and D.S. Chapman (2012), A web-based resource for investigating environmental change: the Emigrant Pass Observatory; Journal of Geoscience Education, v. 60, no. 3, 241 – 248, doi:10.5408/11-252.1.

Davis, M.G., R.N. Harris, and D.S. Chapman (2010), Repeat temperature measurements in boreholes from northwestern Utah link ground and air temperature changes at the decadal time scale; J. of Geophys. Res., v. 115, B05203, doi:10.1029/2009JB006875.

Harris, R.N., and D.S. Chapman (2001), Mid-Latitude (30° – 60° N) climatic warming inferred by combining borehole temperatures with surface air temperatures, Geophys. Res. Lett., 28, 747 – 750.

Huang, S. (2006), Land warming as part of global warming, Eos, 87(44).

Huang, S., H.N. Pollack, and P.-Y. Shen (2000), Temperature trends over the past five centuries reconstructed from borehole temperatures, Nature, 403, 756 – 758.

Intergovernmental Panel on Climate Change (2013), Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Lachenbruch, A.H., and B.V. Marshall (1986), Changing climate: Geothermal evidence from permafrost in the Alaskan Artic, Science, 234, 689 – 696.

Levitus, S., J.I. Antonov, T. P. Boyer, and C. Stephens (2000), Warming of the world ocean, Science, 287, 2225 – 2229, doi:10.1126/science.287.5461.2225.

Levitus, S., J.I. Antonov, J. Wang, T.L. Delworth, K.W. Dixon, and A.J. Broccoli (2001), Anthropogenic warming of Earth’s climate system, Science, 292, 267 – 270, doi:10.1126/science.1058154.

Lewis T. J. and K. Wang (1998), Geothermal evidence of deforestation induced warming: Implications for the climatic impact of land development, Geophys. Res. Lett., 25, 535-538.

Nitoiu, D., and H. Beltrami (2005), Subsurface thermal effects of land use change, J. Geophys. Res., 110, doi:10.1029/2004JF000151.

Putnam, S.N., and D.S. Chapman (1996), A geothermal climate change observatory: First year results from Emigrant Pass in northwest Utah, J. Geophys. Res., 101, 21,877 – 21,890.

Smerdon, J. E., H. N. Pollack, J. W. Enz, and M. J. Lewis (2003), Conduction-dominated heat transport of the annual temperature signal in soil, J. Geophys. Res., 108(B9), 2431, doi:10.1029/2002JB002351.

Smerdon, J. E., H. N. Pollack, V. Cermak, J. W. Enz, M. Kresl, J. Safanda, and J. F. Wehmiller (2004), Air-ground temperature coupling and subsurface propagation of annual temperature signals, J. Geophys. Res., 109, D21107, doi:10.1029/2004JD005056.

Smerdon, J. E., H. N. Pollack, V. Cermak, J. W. Enz, M. Kresl, J. Safanda, and J. F. Wehmiller (2006), Daily, seasonal, and annual relationships between air and subsurface temperatures, J. Geophys. Res., 111, D07101, doi:10.1029/2004JD005578.