Professor, Department of Geosciences
GEOS 318: Earth's Changing Climate
The future of our climate from the perspective of climate system dynamics. The course has three five-week modules. The first covers the processes and time scales governing Earth’s heat balance, the basic rules of changing climate. The second module explores climate variability stemming from internal dynamics of the climate system. The final module examines the grand challenge in climate science: constraining projections of future change with regards to feedbacks and uncertainties in climate system processes. Emerging research is highlighted throughout the course on unsettled scientific problems in climate science and the approaches taken by scientists to solve them.
GEOS 488: Snow Ice and Climate
Frozen water (i.e., glaciers, ice sheets, seasonal snow, and sea ice) is a primary component of Earth's climate system that both drives and responds to climate change. This course examines the role of snow and ice in four key aspects of climate change, highlighting unsolved problems and current research: 1) global sea level rise and stability of ice sheets; 2) Arctic amplification of climate change and sea ice processes; 3) climate system feedbacks revealed by ice cores; and, 4) water supply and mountain snowpack dynamics.
GEOS 508: Fundamentals of Scientific Research
Skills and knowledge needed to perform successfully as a graduate student researcher and to continue as a career scientist. For example: 1) designing research projects having sound scientific reasoning and methods, 2) writing successful grant proposals, and 3) making effective written and oral presentations to scientific peers. The course also explores trends and cultures in science, such as bias, reproducibility, publishing, and education/career trajectories. Intended for first semester graduate students.
GEOS 548: Advanced Topics in the Cryosphere
In-depth study of revolving topics related to the cryosphere involving lectures, readings, discussions, exercises, and original research. Topics of recent semester-long courses include:
-Retention and flow of water in snow
-Development and deployment of field instrumentation
-Sea level rise
GEOS 568: Climate Sensitivity and Feedbacks
Climate sensitivity is a metric of the Earth’s climate system which describes the temperature change resulting from a radiative imbalance (forcing). Climate sensitivity reflects all uncertainties and feedbacks that amplify or dampen forcings. This graduate course examines past, present, and future climate change via the climate sensitivity metric. We investigate the many feedback mechanisms in the climate system, the time scales of climate system response, and the methods for evaluating our climate system’s sensitivity to greenhouse gas forcing.
My research is focused on the interactions and feedbacks between the cryosphere and the climate system. This work is motivated by societal need to understand the climate system, project sea level rise, and manage water resources. I employ methods of computer modeling, data analysis, and field instrumentation. My field research is conducted on the Greenland Ice Sheet, small glaciers in Alaska and Montana, and seasonal snow in Montana. My research is funded by the U.S. National Science Foundation, NASA, and the Swedish Nuclear Waste Management Company.
Field of Study
Undergraduate student Max Hanna working with me on the Greenland ice sheet. Max spent five weeks in Greenland between his junior and senior years. Thanks for the help Max!
Maier, N., Humphrey, N., Harper, J., & Meierbachtol. T. (2019). Sliding dominates slow-flowing margin regions, Greenland Ice Sheet. Science Advances, 5(7). https://doi.org/10.1126/sciadv.aaw5406.
Doyle, S. H. et al. (2015), Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall, Nature Geos., 8(8), 647–653, doi:10.1038/ngeo2482.
Harper, J. (2013), Cryosphere: Greenland’s lurking aquifer, Nature Geos., 7(2), 86–87, doi:10.1038/ngeo2061.
Meierbachtol, T., J. Harper, and N. Humphrey (2013), Basal Drainage System Response to Increasing Surface Melt on the Greenland Ice Sheet, Science, 341(6147), 777–779, doi:10.1126/science.1235905.
Harper, J. T., N. Humphrey, W. T. Pfeffer, J. Brown, and X. Fettweis (2012), Greenland ice-sheet contribution to sea-level rise buffered by meltwater storage in firn., Nature, 491(7423), 240–3, doi:10.1038/nature11566.
Harper, J. T., J. H. Bradford, N. F. Humphrey, and T. W. Meierbachtol (2010), Vertical Extension of the Subglacial Drainage System Into Basal Crevasses, Nature, 467, 579–582, doi:10.1038/nature09398.
Pfeffer, W. T., J. T. Harper, and S. O’Neel (2008), Kinematic constraints on glacier contributions to 21st-century sea-level rise, Science, 321 (5894), 1340–1343, doi: 0.1126/science.1159099.
Harper, J. T., N. F. Humphrey, and W. T. Pfeffer (1998), Three-dimensional deformation measured in an Alaskan Glacier, Science, 281(5381), 1340–1342.
Discipline-specific Journals and Chapters
Maier N, Humphrey N, Meierbachtol T, Harper J (2021). Deformation motion tracks sliding changes through summer, western Greenland. Journal of Glaciology, 1–10. https://doi.org/10.1017/jog.2021.87.
Humphrey NF, Harper JT, Meierbachtol TW (2021). Physical limits to meltwater penetration in firn. Journal of Glaciology, 1–9. https://doi.org/10.1017/jog.2021.44.
McDowell, I. E., Humphrey, N. F., Harper, J. T., & Meierbachtol, T. W. (2021). The cooling signature of basal crevasses in a hard-bedded region of the Greenland Ice Sheet. The Cryosphere, 15(2), 897–907. https://doi.org/10.5194/tc-15-897-2021.
Fischer, U., Bebiolk, A., Brandefelt, J., Cohen, D., Harper, J., Hirschorn, S., Jensen, M., Kennell, L., Liakka, J., Näslund, J., Normani, S., Stück, H., Weitkamp, A. (2021), Radioactive Waste Under Conditions of Future Ice Ages, Elsevier Book Series, Snow and Ice-Related Hazards, Risks and Disasters, Eds. W. Haeberli C. Whiteman, 2nd Edition, ISBN: 9780128171295, 700 p.
Leone, R., Harper, J., Meierbachtol, T., & Humphrey, N. (2020). Horizontal Ice Flow Impacts the Firn Structure of Greenland’s Percolation Zone. The Cryosphere, 14, 2020, 1703–1712. https://doi.org/doi.org/10.5194/tc-14-1703-2020.
Humphrey N, Harper J, Meierbachtol T (2020). Hot water drilling in the firn layer of Greenland’s percolation zone. Annals of Glaciology, 1–4. https://doi.org/10.1017/aog.2020.75.
Elser, J. J., Wu, C., González, A. L., Shain, D. H., Smith, H. J., Sommaruga, R., et al. (2020). Key rules of life and the fading cryosphere: Impacts in alpine lakes and streams. Global Change Biology, 26(12), 6644–6656. https://doi.org/10.1111/gcb.15362.
Florentine, C., Harper, J., & Fagre, D. (2020). Parsing complex terrain controls on mountain glacier response to climate forcing. Global and Planetary Change, 191(September 2019), 103209. https://doi.org/10.1016/j.gloplacha.2020.103209
Jaquet, O., Namar, R., Siegel, P., Harper, J. and P. Jansson (2019), Groundwater flow modelling under transient ice sheet conditions in Greenland, Svensk Kärnbränslehantering AB., Reviewed Technical Report (RTR) R-19-17: Stockholm Sweden, ISSN 1402-3091 , 123 p.
Harper, J.T, Meierbachtol, T.W. and N.F. Humphrey, (2019), Scaling Physical Conditions and Processes at the Bed of the Greenland Ice Sheet, Svensk Kärnbränslehantering AB., Reviewed Technical Report (RTR) R-18-06: Stockholm Sweden, ISSN 1402-3091 , 117 p.
Hills, B. H., Harper, J. T., Meierbachtol, T. W., Johnson, J. V., Humphrey, N. F., & Wright, P. J. (2018). Processes influencing near-surface heat transfer in Greenland’s ablation zone. The Cryosphere, 12, 3215–3227. https://doi.org/https://doi.org/10.5194/tc-12-3215-2018
Florentine, C., Harper, J., Fagre, D., Moore, J., & Peitzsch, E. (2018). Local topography increasingly influences the mass balance of a retreating cirque glacier. The Cryosphere, 12(6), 2109–2122. https://doi.org/10.5194/tc-12-2109-2018
Florentine, C., Harper, J., Johnson, J., & Meierbachtol, T. (2018). Radiostratigraphy Reflects the Present-Day, Internal Ice Flow Field in the Ablation Zone of Western Greenland. Frontiers in Earth Science, 6(April). https://doi.org/10.3389/feart.2018.00044
Meierbachtol, T. W., Harper, J. T., & Humphrey, N. F. (2018). Short duration water pressure transients in western Greenland’s subglacial drainage system. Journal of Glaciology, 64(243), 171–174. https://doi.org/10.1017/jog.2018.9
Downs, J. Z., Johnson, J. V., Harper, J. T., Meierbachtol, T., & Werder, M. A. (2018). Dynamic Hydraulic Conductivity Reconciles Mismatch Between Modeled and Observed Winter Subglacial Water Pressure. Journal of Geophysical Research: Earth Surface, 123(4), 818–836. https://doi.org/10.1002/2017JF004522
Woelber, B., Maneta, M. P., Harper, J., Jencso, K. G., Payton Gardner, W., Wilcox, A. C., & López-Moreno, I. (2018). The influence of diurnal snowmelt and transpiration on hillslope throughflow and stream response. Hydrology and Earth System Sciences, 22(8), 4295–4310. https://doi.org/10.5194/hess-22-4295-2018
Harper, J. T., Humphrey, N. F., Meierbachtol, T. W., Graly, J. A., & Fischer, U. H. (2017). Borehole Measurements Indicate Hard Bed Conditions, Kangerlussuaq Sector, Western Greenland Ice Sheet. Journal of Geophysical Research: Earth Surface, 1–14. doi.org/10.1002/2017JF004201.
Hills, B. H., Harper, J. T., Humphrey, N. F., & Meierbachtol, T. W. (2017). Measured horizontal temperature gradients constrain heat transfer mechanisms in Greenland ice. Geophysical Research Letters. doi.org/10.1002/2017GL074917.
Brown, J, Harper, J, Humphrey, N., (2017) Liquid water content in ice estimated through a full-depth ground radar profile and borehole measurements in western Greenland. The Cryosphere, 11, 1–11, doi:10.5194/tc-11-1-2017.
Clark, A., Fagre, D., Peitzsch, E., Reardon, B., and Harper, J. (2017), Glaciological measurements and mass balances from Sperry Glacier, Montana, USA, years 2005–2015, Earth Syst. Sci. Data, 9, 47-61, doi:10.5194/essd-9-47-2017.
Meierbachtol, T., J. Harper, and J. Johnson (2016), Force Balance along Isunnguata Sermia, West Greenland, Frontiers of Earth Science., 4, 1–9, doi:10.3389/feart.2016.00087.
Wright, P. J., J. T. Harper, N. F. Humphrey, and T. W. Meierbachtol (2016), Measured basal water pressure variability of the western Greenland Ice Sheet: Implications for hydraulic potential, J. Geophys. Res., 121, 1–14, doi:10.1002/2016JF003819.
Graly, J. A., N. F. Humphrey, and J. T. Harper (2016), Chemical depletion of sediment under the Greenland Ice Sheet, Earth Surf. Process. Landforms, 1–15, doi:10.1002/esp.3960.
Harper, J, Hubbard, A, Ruskeeniemi, T, Claesson Liljedahl, L., Kontula, A, Hobbs, M, Brown, J, Dirkson, A, Dow, C, Doyle, S, Drake, H, Engström, J, Fitzpatrick, A, Follin, S, Frape, S. (2016), The Greenland Analogue Project: Data and Processes, Svensk Kärnbränslehantering AB., R-14-13, Stockholm Sweden, ISSN 1402-3091, 387p.
Claesson Liljedahl, L., Kontula, A, Harper, J, J-o, Näslund, J-o, Selroos, Pitkänen, P, Puigdomenech, I, Hobbs, M, Follin, S, Hirschorn, S, Jansson, P, Kennell, L, Marcos, N, Ruskeeniemi, T, E-l, Tullborg, Vidstrand, P (2016), The Greenland Analogue Project, Svensk Kärnbränslehantering AB., R-14-13, Stockholm Sweden, ISSN 1404-0344, 142p.
Meierbachtol, T.W., J. T. Harper, N. F. Humphrey, and P. Wright (2015), Mechanical Forcing on Water Pressure in a hydrologically isolated reach beneath Western Greenland’s ablation zone, Annals of Glaciology, 1–9, doi:10.1017/aog.2016.5.
Cox, C., N. Humphrey, and J. Harper (2015), Quantifying meltwater refreezing along a transect of sites on the Greenland ice sheet, Cryosphere, 9, 691–701, doi:10.5194/tc-9-691-2015.
Clark, A. M., Harper, J. T., and D.B. Fagre, (2015), Glacier-derived August runoff in northwest Montana. Arctic, Antarctic, and Alpine Research, Vol. 47, No. 1, 1–16.
Harrington, J., Humphrey, N.F., and J. T. Harper, (2015), Temperature distribution and thermal anomalies along a flowline of the Greenland Ice Sheet, Annals of Glaciology, Vol. 56, No. 70, 70A945.
Meierbachtol, T. W., Harper, J. T., Johnson, J. V., Humphrey, N. F., and D. J. Brinkerhoff, (2015), Thermal boundary conditions on Western Greenland: observational constraints and impacts on the modeled thermo-mechanical state. Journal of Geophysical Research Earth Surface, DOI: 10.1002/2014JF003375.
Graly, J. A., N. F. Humphrey, C. M. Landowski, and J. T. Harper (2014), Chemical weathering under the Greenland Ice Sheet, Geology, 42(6), 551–554, doi:10.1130/G35370.1.
Seligman, Z. M., J. T. Harper, and M. P. Maneta (2014), Changes to Snowpack Energy State from Spring Storm Events, Columbia River Headwaters, Montana, J. Hydrometeorol., 15(1), 159–170, doi:10.1175/JHM-D-12-078.1.
Bradford, J. H., J. Nichols, J. T. Harper, and T. Meierbachtol (2013), Compressional and EM wave velocity anisotropy in a temperate glacier due to basal crevasses, and implications for water content estimation, Ann. Glaciol., 54(64), 168–178, doi:10.3189/2013AoG64A206.
Rennermalm, a K. et al. (2013), Understanding Greenland ice sheet hydrology using an integrated multi-scale approach, Environ. Res. Lett., 8(1), 015017, doi:10.1088/1748-9326/8/1/015017.
Silverman, N. L., M. P. Maneta, S.-H. Chen, and J. T. Harper (2013), Dynamically downscaled winter precipitation over complex terrain of the Central Rockies of Western Montana, USA, Water Resour. Res., 49(1), 458–470, doi:10.1029/2012WR012874.
Brown, J., J. Bradford, J. Harper, W. T. Pfeffer, N. Humphrey, and E. Mosley-Thompson (2012), Georadar-derived estimates of firn density in the percolation zone, western Greenland ice sheet, J. Geophys. Res., 117(F1), F01011, doi:10.1029/2011JF002089.
Humphrey, N. F., J. T. Harper, and W. T. Pfeffer (2012), Thermal tracking of meltwater retention in Greenland’s accumulation area, J. Geophys. Res., 117(F1), F01010, doi:10.1029/2011JF002083.
Mikesell, T. D., K. van Wijk, M. M. Haney, J. H. Bradford, H. P. Marshall, and J. T. Harper (2012), Monitoring glacier surface seismicity in time and space using Rayleigh waves, J. Geophys. Res., 117(F2), F02020, doi:10.1029/2011JF002259.
Brinkerhoff, D. J., T. W. Meierbachtol, J. V Johnson, and J. T. Harper (2011), Sensitivity of the frozen/melted basal boundary to perturbations of basal traction and geothermal heat flux: Isunnguata Sermia, western Greenland, Ann. Glaciol., 52(59), 43–50.
Brown, J., J. Harper, W. T. Pfeffer, N. Humphrey, and J. Bradford (2011), High-resolution study of layering within the percolation and soaked facies of the Greenland ice sheet, Ann. Glaciol., 52(59), 35–42.
Harper, J., N. Humphrey, W. T. Pfeffer, and J. Brown (2011), Firn Stratigraphy and Temperature to 10 m Depth in the Percolation Zone of Western Greenland, 2007–2009, INSTAAR, Occas. Pap., ISSN 0069-(60).
Brown, J., J. Harper, and N. Humphrey (2010), Cirque Glacier Sensitivity to 21st Century Climate Change: Sperry Glacier, Montana, Glob. Planet. Change, 74(2), 91–98, doi:10.1016/j.gloplacha.2010.09.001.
Gillan, B. J., J. T. Harper, and J. N. Moore (2010), Timing of present and future snowmelt from high elevations in northwest Montana, Water Resour. Res., 46, W01507, doi:doi:10.1029/2009WR007861.
Bradford, J. H., J. T. Harper, and J. Brown (2009a), Complex dielectric permittivity measurements from ground-penetrating radar data to estimate snow liquid water content in the pendular regime, Water Resour. Res., 45, 1–12, doi: 10.1029/2008WR007341.
Bradford, J. H., J. Nichols, M. T. D., and J. T. Harper (2009b), Continuous Profiles Of Electromagnetic Wave Velocity and Water Content in Glaciers, Ann. Glaciol., 50(51), 1–9.
Brown, J., J. Harper, and J. Bradford (2009), A radar transparent layer in a temperate valley glacier: Bench Glacier, Alaska, Earth Surf. Process. Landforms, 34, 1497–1506, doi: 10.1002/esp.1835.
Fudge, T. J., J. T. Harper, N. F. Humphrey, and W. T. Pfeffer (2009), Rapid Glacier Sliding, Reverse Ice Motion, and Subglacial Water Pressure During an Autumn Rainstorm, Ann. Glaciol., 50(51), 1–9.
Fudge, T. J., N. F. Humphrey, J. T. Harper, and W. T. Pfeffer (2008), Diurnal Fluctuations in Borehole Water Levels: Configuration of the Drainage System Beneath Bench Glacier, Alaska, J. Glaciol., 54(185), 297–306, doi 10.3189/002214308784886072.
Meierbachtol, T., J. T. Harper, N. F. Humphrey, J. Shaha, and J. Bradford (2008), Air compression as a mechanism for the underdamped slug test response in fractured glacier ice, J. Geophys. Res., 113(F04009), 1–14, doi: 10.1029/2007JF000908.
Bleha, J. A., and J. T. Harper (2007), Snowmelt Water Generation in a Large Mountain Basin of Northwest Montana from a MODIS Driven Model, in Symposium on Environmental Sensing, vol. 1, edited by M. Gribb, pp. 83–86. , Inland Northwest Research Alliance, Boise, ID.
Harper, J. T., N. F. Humphrey, W. T. Pfeffer, and B. Lazar (2007), Two modes of Accelerated Glacier Sliding Related to Water, Geophys. Res. Lett., 34(12), L12503, doi: 10.1029/2007GL030233.
Moore, J. N., J. T. Harper, and M. C. Greenwood (2007), Significance of trends toward earlier snowmelt runoff, Columbia and Missouri Basin headwaters, western United States, J. Geophys. Res., 34, L16402, doi:10.1029/2007GL031022, doi:10.1029/2007GL031022.
Bradford, J. H., and J. T. Harper (2006), Measuring complex dielectric permittivity from GPR to estimate liquid water content in snow, Soc. Explor. Geophys. Tech. Progr., 25, 1352–1356, doi:10.1190/1.2369770.
Bradford, J. H., and J. T. Harper (2005), Wavefield Migration as a Tool for Estimating Spatially Continuous Radar Velocity and Water Content in Glaciers, Geophys. Res. Lett., 32, L08502, doi:10.1029/2004GL021770.
Fudge, T. J., J. T. Harper, N. F. Humphrey, W. T. Pfeffer, (2005), Timing and pattern of termination of diurnal water pressure fluctuations: Bench Glacier, Alaska, Ann. Glaciol., 40, 102–106.
Harper, J. T., N. F. Humphrey, W. T. Pfeffer, T. Fudge, and S. O’Neel (2005), Evolution of subglacial water pressure along a glacier’s length, Ann. Glaciol., 40, 31–36.
Harper, J. T., and J. H. Bradford (2003), Snow stratigraphy over a uniform depositional surface: spatial variability and measurement tools, Cold Reg. Sci. Technol., 37(3), 289–298.
Harper, J. T., N. F. Humphrey (2003), High altitude Himalayan climate inferred from glacial ice flux, Geophys. Res. Lett., 30(14), 1764–1769, doi:10.1029/2003GL017329.
Harper, J. T., and J. H. Bradford (2002), Spatial variability of snow stratification in the absence of terrain factors, in International Snow Science Workshop, edited by R. Stevens, pp. 1–8, International Snow Science Workshop Canada Inc., Penticton, B.C. Canada.
Harper, J. T., N. F. Humphrey, M. C. Greenwood (2002), Basal conditions and glacier motion during the winter/spring transition, Worthington Glacier, Alaska, U.S.A, J. Glaciol., 48(160), 42–50, doi:10.3189/172756502781831629.
Marshall, H. P., J. T. Harper, W. T. Pfeffer, and N. F. Humphrey (2002), Depth-varying constitutive properties observed in an isothermal glacier, Geophys. Res. Lett., 29(61), 1–4.
Harper, J. T., N. F. Humphrey, W. T. Pfeffer, S. V Huzurbazar, D. B. Bahr, B. C. Welch, and Anonymous (2001), Spatial variability in the flow of a valley glacier: Deformation of a large array of boreholes, J. Geophys. Res., 106(B5), 8547–8562, doi: 10.1029/2000JB900440.
Pfeffer, W. T., N. F. Humphrey, B. Amadei, J. T. Harper, and W. J. (2000), In-situ stress tensor measured in an Alaskan glacier, Ann. Glaciol., 31, 229–235.
Harper, J. T., N. F. Humphrey, and W. T. Pfeffer (1998a), Crevasse patterns and the strain rate tensor: a high resolution comparison, J. Glaciol., 44(146), 68–76.
Jones, L. S., and J. T. Harper (1998), Channel avulsions and related processes, and large-scale sedimentation patterns since 1875, Rio Grande, San Luis Valley, Colorado, Geol. Soc. Am. Bull., 110(3), 411–421.
Welch, B. C., W. T. Pfeffer, J. T. Harper, and N. F. Humphrey (1998), Mapping subglacial surfaces below temperate valley glaciers using 3-dimensional radio-echo sounding techniques, J. Glaciol., 44(146), 164–170.
Harper, J. T., N. F. Humphrey, W. T. Pfeffer, and B. C. Welch (1996), Short wavelength variations in the horizontal velocity field of a valley glacier, in Glaciers, Ice Sheets and Volcanoes, vol. Special Re, edited by S. C. Colbeck, pp. 41–48, U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, N.H.
Welch, B. C., W. T. Pfeffer, J. T. Harper, and N. F. Humphrey (1996), A maximum glacier-bed surface obtained by radio-echo sounding, in Glaciers, Ice Sheets and Volcanoes, vol. Special Re, edited by S. C. Colbeck, pp. 105–110, U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, N.H.
Harper, J. T., and N. F. Humphrey (1995), Borehole video analysis of a temperate glacier’s englacial and subglacial structure; implications for glacier flow models, Geology, 23(10), 901–904.
Harper, J. T. (1993), Glacier terminus fluctuations on Mount Baker, Washington, U.S.A., 1940-1990, and climatic variations, Arct. Alp. Res., 25(4), 332–340.