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Borehole Temperatures
Evidence for warming of the planet in the last five centuries can be found in the
geothermal observations from
boreholes on several continents.
The procedure for recovering information about global warming from these records is
described by NOAA.
Data from boreholes at least 200 m deep, and in some cases as much as 600 m deep, have been
analyzed. Data above 20 m have been omitted because they include annual variability which
obscures the global warming trend, and data below 600 m have not been included because they
contain no information about the past 500 years. Comparison of the borehole temperatures
with surface air temperatures in the last 150 years show that the two datasets are in
agreement, and there is some suggestion that the rate of warming in the geothermal data has increased in
the 20th century in agreement with the accelerated warming of the air temperature record.
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