Science project

Soil Temperature & Global Warming

Global surface temperatures have increased by an average of 0.74 deg C (plus or minus 0.18 deg C) since the late 19th century. The trend over the past 50 years corresponds to an increase in temperature of 0.13 deg C (plus of minus 0.03 deg C) per decade. This is more than twice that for the past 100 years. Seven of the eight warmest years on record have occurred since 2001. The ten warmest years on record have all occurred since 1995.


Is soil temperature a good indicator of global warming trends? How does soil temperature vary with depth from the surface?


  • Auger hand post hole digger
  • Extension shafts
  • Soil thermometer
  • Tape measure


  1. Read about global surface temperature trends and global warming. Also read about soil layering.
  2. Formulate a hypothesis about whether soil temperature data could be used to reconstruct global warming trends.
  3. Select a location to obtain a soil temperature profile.
  4. Measure the temperature of the soil at ground level.
  5. Dig 6 inches into the ground, and measure the soil temperature there.
  6. Dig down another 6 inches and check the soil temperature again.
  7. Continue these measurements every 6 inches until there are no further variations in soil temperature with depth or until you can dig no further.
  8. Repeat these measurements at two more locations, at times spaced a month apart.
  9. Estimate the soil temperature at the depth where the temperature no longer depends on surface temperature (or use your measured value) for each of the three months in your study.
  10. Tabulate and plot this temperature versus time.
  11. Evaluate your hypothesis and revise it if necessary.

Depth (ft)

Soil Temperature (deg C)

Month 1

Month 2

Month 3




Author: Randall Frost, Ph.D.
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