Hehehehehe... "borehole"
Posted on 04/17/2002 9:15:35 AM PDT by cogitator
Rock Measurements Suggest Warming is Global
ANN ARBOR, Michigan, April 16, 2002 (ENS) - Over the past 50 years, the rocks of Earth's continental crust have warmed in concert with the warming of the oceans, atmosphere and ice, says a team of Michigan and Canadian researchers.
"Our findings remove any last doubt that this is anything other than a global phenomenon," said Henry Pollack, University of Michigan (UM) professor of geological sciences.
"Until recently, the story of global warming has been built up primarily on the basis of temperature measurements at the surface of the land and oceans," said Pollack. "These measurements have been painstakingly acquired and put together, and there has been enough information to reconstruct a temperature history for the Earth's surface for the past 140 years. But it's all based on surface measurements."
About a year ago, a group of researchers determined how much heat had been gained during the last half of the 20th century throughout the atmosphere, the depths of the oceans, and the cryosphere - the portion of Earth's surface where water is in solid form such as sea ice, snow cover, glaciers, ice caps and permafrost.
However, their analysis left out one major component of the climate system: continental rock, which covers almost 30 percent of the planet's surface.
Now, Pollack and colleagues have completed the picture by determining how much the continental rock has warmed in recent centuries.
The scientists based their analysis on temperature readings taken by lowering sensitive thermometers into holes drilled from Earth's surface into rock formations on six continents, including Africa, Asia, Europe, North America, South America and Australia. These readings can reveal how temperatures have changed in the past, because the heat that surface rocks absorb from the atmosphere travels downward into subsurface rocks, leaving a distinct signature in the rocks.
Signals from short term daily or seasonal variations penetrate just a few meters, but temperature changes that take place over hundreds of years are preserved in deeper rock.
The researchers' calculations, based on data from 616 bore holes, found evidence of an increase in the heat content of the continents over the past 500 years, with more than half of that heat gain occurring during the 20th century, and almost one-third of it since 1950.
"The magnitude of the warming we estimate is very similar to that which has come from the studies of the ocean, atmosphere and ice," said Pollack. "We believe it makes a persuasive case that the warming has been truly global."
The research is reported in the April 15 issue of the geology journal "Geophysical Research Letters."
How can they tell ?
In addition, a 50 year time span is meaningless on a geological scale that operates over thousands or millions of year for even slight changes. Any data over 50 years represents only noise (i.e. natural variation) on the geologic time scale.
Gore the boring a-hole = Borehole.
I can't believe my mind made that connection without even thinking about it-----I've been FReeping for too long.
Every liberal is a thug.
They may have, but they may also be more subject to perturbation (particularly for caves open to the public) and the signal may not be as easy to measure as for a small borehole created by drilling. Plus, the caves usually have an extensive groundwater system that might transfer heat. Good question to ask!
The borehole method only measures trend and does not investigate cause. Actual attribution of cause requires modeling, but having an accurate temperature record is important to check the model output accuracy. If the borehole records do support the surface temperature warming pattern, then that pattern is the one that the models must analyze.
Temperature trends over the past five centuries reconstructed from borehole temperatures
SHAOPENG HUANG*, HENRY N. POLLACK* & PO-YU SHEN†
Nature 403, 756 - 758 (2000)
Excerpt 1: "The thermal regime of the uppermost continental crust is determined in part by the outward flow of heat from the deep interior of the Earth and in part by fluctuations of temperature at the surface. In homogeneous rock and in the absence of changes at the surface, the temperature in the subsurface increases linearly with depth, at a rate which is governed by the magnitude of the terrestrial heat flow and the thermal conductivity of the rock. Fluctuations of surface temperature propagate downward into the rock as attenuating thermal waves superimposed on the temperature profile associated with the deeper heat flow. The depth to which disturbances can be observed is determined by the amplitude, duration and spectral composition of the temperature change at the surface. Owing to the generally low thermal diffusivity of rock, propagation of climate signals in the subsurface is slow. Following a change in temperature at the surface, it takes about 100 years for the perturbation to reach a depth of 150 m, and 1,000 years to reach 500 m depth. Complications in reconstructing a ground surface temperature (GST) history from subsurface temperature data can, however, arise from various non-climatic disturbances7 that perturb subsurface temperatures."
Excerpt 2:
"The reconstruction of a GST history by inversion of subsurface temperatures has its foundation in the theory of heat conduction9-11. Because of the diffusion of the climate signal through the rocks, a geothermal climate reconstruction is characterized by a progressive inability to resolve the details of climate excursions in the more remote past12-14. For inverting subsurface temperatures to yield a GST history, we use a bayesian estimation technique15 that is a simplification and extension of the functional space inversion formulation of Shen and Beck16. Rather than treating the GST history as an arbitrary function of time, we have chosen to parametrize the reconstruction simply, in terms of century-long rates of change over the past five centuries. This simple parametrization leads to a very smooth GST reconstruction. The absence of shorter-period representation in the reconstruction, however, is offset by a reduction of variance in the estimated century-long rates, and by the ease with which these rates may be compared to corresponding quantities that emerge from analyses of the instrumental record. If climate-change trends do not coincide closely with the calendar centuries, such as when a natural century-long trend straddles two calendar centuries, the inversion will attribute part to one century and part to the other, thus creating a temporal smearing of the temperature trend. In the inversion we employ an a priori null hypothesis for the GST history; that is, an initial estimate that there has been no climate change. This is a conservative hypothesis that is also fully independent of any extant models of climate change. As resolution diminishes further back in time, the null hypothesis becomes more difficult to reject."
Excerpt 3: "Although the mechanism of the coupling between the air temperature at the surface and the GST is not simple, and varies from one geographical setting to another18-20, at a large spatial scale the trends of the surface air temperature anomaly and the GST anomaly match well (Fig. 2). Both the global mean surface air temperature (SAT) anomaly series6 and the GST continental reconstruction show substantial warming in the twentieth century. The geothermal reconstruction is in generally good agreement with the trend of the global SAT record in both the late nineteenth and twentieth centuries, and extends the climate history back several hundred years before the instrumental record. Almost 80% of the net temperature increase observed has occurred in the nineteenth and twentieth centuries."
For references 18-20, 18 appears to be the most informative but there's no way I'm going to find it online:
Chapman, D.S., Chisolm, T.J. & Harris, R.N. Combining borehole temperature and meteorological data to constrain past climate change. Palaeogeogr. Palaeoclimatol. Palaeoecol. 98, 269-281 (1992).
Now, look, I use the term "enviro-nazi" on purpose and I think you know why. There means and objective are quite well known and this is the reason you get so much flack when you post quite well-intentioned articles here.
You won't find me trying to argue that there does not appear to be a warming trend in the recent, extremely short-term, data. You will find me smacking down ruthlessly any closet marxist who starts claiming that the automobile is the greatest threat to mankind and that our entire approach to society change ought to be based around an ideology of preserving mother earth first.
Hehehehehe... "borehole"
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