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8 Boreholes
Pages 77-82

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From page 77...
... · Temperatures inferred from borehole data are not calibrated against the instrumental temperature record, thereby providing an independent mea surement of past temperature. · For the period 1600­1900, borehole-based temperature reconstruc tions have century-scale resolution and thus provide information about long term temperature trends, but not about decadal or annual variations.
From page 78...
... Important quantitative uncertainties exist, but general trends in these reconstructions are likely robust. Borehole-based temperature reconstructions averaged for broad regions (including eastern North America, western North America, Europe, Australia, and South Africa)
From page 79...
... and uses the instrumental temperature record from 1856 onward. The measured subsurface temperature pattern (bottom panel, black circles)
From page 80...
... However, the similarity between measured ground temperatures and ground temperatures calculated using air temperatures (Harris and Chapman 2001) suggests that the average bias must be small over the middle latitudes.
From page 81...
... shows no consistent offset related to precipitation: borehole-inferred warming exceeds instrumental warming in the wet regions of North America but is less than instrumental warming in the wet regions of Europe and Southeast Asia. This is further evidence that the groundwater bias is quantitatively small in borehole-based temperature reconstructions on larger scales.
From page 82...
... Uncertainties on these results for earlier time periods are on the order of a few tenths of a degree Celsius for averages over a few centuries.


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