Image:Boreholes Locations.png

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Description

A comparison of a borehole temperature reconstruction to the instrumental temperature record since 1850.

This map shows the locations of the 951 boreholes in the University of Michigan global database of boreholes used to reconstruct past temperatures.

Rock has a very low thermal conductivity which means that it can take centuries for rocks underground to become aware of changes in surface temperatures. By taking very careful measurements of the temperature of rock in boreholes tens and hundreds of meters underground, it is possible to detect shifts in the long-term mean surface temperature at that location. However, as thermal diffusion is such a slow process, short term changes are averaged out and this technique only provides information about changes in the long-term average temperature, often reported with a single measurement per century.

Unlike most other methods for studying paleoclimate, borehole thermometry is a direct measurement of temperature and doesn't need to be calibrated against the instrumental record. Hence, borehole thermometry provides and independent record of paleoclimate against which other paleoclimate techniques can be validated.

Copyright

This image was prepared by Robert A. Rohde.

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