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1.
Inverse and direct methods have been used to analyze a large number of borehole temperature logs in order to infer past climatic changes. Results indicate a warming of 1–2°C in eastern and central Canada during the past 150 years. A period of cooling between 500 and 200 years before present, corresponding to the time of the “Little Ice Age”, has also been identified in the same areas. A regional ground temperature history is estimated for eastern and central Canada from the simultaneous inversion of several temperature logs. The inferred temperature changes appear correlated with the concentration of atmospheric carbon dioxide as reported from a Greenland ice core, and agree with existing meteorological and dendrochronological records for the area.  相似文献   

2.
Several temperature–depth profiles recorded at Pipe Mine, 32 km southwest of Thompson, Manitoba, in central Canada, exhibit a marked departure from the equilibrium gradient. These profiles could be interpreted as indicating strong warming (up to 4.5 K) of the ground surface during the last 200 years. All the temperature profiles at Pipe Mine show perturbations stronger than at the others sites in the Thompson Nickel Belt. Temperature profiles recorded near the town of Thompson show a moderate warming (≈1–2 K) trend, while temperature profiles at Soab, 45 km southwest of Pipe Mine, indicate very moderate cooling (≈0.5 K). There was little human activity in this part of Manitoba before the development of the mining camp of Thompson in the late 1950s. Our study shows the variability of ground surface temperature histories at a very local scale (i.e. <1 km) with much stronger signals at some of the Pipe Mine drill holes than at others. These holes are located within 500 m of the highway and a power line built after 1955, at ≈3 km from the now abandoned open pit mine. The ground surface temperature history (GSTH) obtained by the inversion of Pipe Mine temperature profiles suggests that a recent (50 years) and strong (≈1–2 K) ground surface warming is superimposed on a 1–2 K warming trend that started 200 years ago, without any indication of a cold (little ice ages) episode before. The recent warming (40 years) at Pipe Mine is only a local effect and is likely to be related to the presence of the highway. Before 1960, the ground surface temperature history for Pipe is similar to other sites in the Thompson region. Ground surface temperature histories from other profiles within and near the city of Thompson seem less affected by environmental perturbations and their trends are parallel to that of the meteorological records in the Canadian Prairies.  相似文献   

3.
New temperature logs in wells located in the grassland ecozone in the Southern Canadian Prairies in Saskatchewan, where surface disturbance is considered minor, show a large curvature in the upper 100 m. The character of this curvature is consistent with ground surface temperature (GST) warming in the 20th century. Repetition of precise temperature logs in southern Saskatchewan (years 1986 and 1997) shows the conductive nature of warming of the subsurface sediments. The magnitude of surface temperature change during that time (11 years) is high (0.3–0.4°C). To assess the conductive nature of temperature variations at the grassland surface interface, several precise air and soil temperature time series in the southern Canadian Prairies (1965–1995) were analyzed. The combined anomalies correlated at 0.85. Application of the functional space inversion (FSI) technique with the borehole temperature logs and site-specific lithology indicates a warming to date of approximately 2.5°C since a minimum in the late 18th century to mid 19th century. This warming represents an approximate increase from 4°C around 1850 to 6.5°C today. The significance of this record is that it suggests almost half of the warming occurred prior to 1900, before dramatic build up of atmospheric green house gases. This result correlates well with the proxy record of climatic change further to the north, beyond the Arctic Circle [Overpeck, J., Hughen, K., Hardy, D., Bradley, R., Case, R., Douglas, M., Finney, B., Gajewski, K., Jacoby, G., Jennings, A., Lamourex, S., Lasca, A., MacDonald, G., Moore, J., Retelle, M., Smith, S., Wolfe, A., Zielinski, G., 1997. Arctic environmental change of the last four centuries, Science 278, 1251–1256.].  相似文献   

4.
Climatic temperature changes at the ground surface propagate downward to the subsurface creating transient disturbances to the temperature—depth (T(z)) profile. Due to the poor thermal diffusivity of rocks the disturbances are preserved long times in the bedrock, and in a conductive regime it is possible to reveal the ground surface temperature (GST) history from borehole temperature data with inversion techniques. Geothermal temperature measurements thus provide a source of palaeoclimatic information which so far has not been utilized extensively. Inversion of GST history is, however, not straightforward and any disturbing effects should be excluded before the data can be utilized in inversion. Groundwater flow is of special importance in this respect because it is a common phenomenon in bedrock and convection often produces temperature—depth profiles resembling those affected by palaeoclimatic GST changes. In interpreting temperature—depth (T(z)) logs it is therefore not always clear whether the recorded vertical gradient variations should be attributed to the effects of palaeoclimatic ground surface temperature (GST) changes or to groundwater circulation. Using several synthetic T(z) profiles and applying general least squares inversion techniques we simulate a situation of “misinterpreting” the curvature of the T(z) profile in terms of palaeoclimatic GST changes, although it is actually produced by convective heat transfer due to groundwater flow. For comparison the opposite case is also studied, namely, genuine palaeoclimatic effects are misinterpreted as being due to disturbances caused by groundwater flow. A homogeneous half-space model is used to model T(z) profiles disturbed conductively by GST changes during the time interval 10–10000 yr B.P. and a one-dimensional porous layer model is applied for convective heat transfer calculations. The results indicate that a given T(z) profile can be attributed to either of these effects with reasonable parameter values. In addition to the synthetic T(z) profiles, a case history from a 958 m deep drill hole at Lavia, southwestern Finland, is presented. Special care is needed in analyzing T(z) data. A knowledge of geothermal data, such as temperature, thermal conductivity and diffusivity is not necessarily adequate for determining which of the phenomena (or whether a combination of them) provides the most probable interpretation of a T(z) profile. Additional information on the hydrogeological properties of the drilled strata is essential.  相似文献   

5.
Warming permafrost in European mountains   总被引：3，自引：0，他引：3  
Here we present the first systematic measurements of European mountain permafrost temperatures from a latitudinal transect of six boreholes extending from the Alps, through Scandinavia to Svalbard. Boreholes were drilled in bedrock to depths of at least 100 m between May 1998 and September 2000. Geothermal profiles provide evidence for regional-scale secular warming, since all are nonlinear, with near-surface warm-side temperature deviations from the deeper thermal gradient. Topographic effects lead to variability between Alpine sites. First approximation estimates, based on curvature within the borehole thermal profiles, indicate a maximum ground surface warming of +1 °C in Svalbard, considered to relate to thermal changes in the last 100 years. In addition, a 15-year time series of thermal data from the 58-m-deep Murtèl–Corvatsch permafrost borehole in Switzerland, drilled in creeping frozen ice-rich rock debris, shows an overall warming trend, but with high-amplitude interannual fluctuations that reflect early winter snow cover more strongly than air temperatures. Thus interpretation of the deeper borehole thermal histories must clearly take account of the potential effects of changing snow cover in addition to atmospheric temperatures.  相似文献   

6.
Accurate temperature–depth profiles may help to assess the temperature variations associated with the climate changes in the past. Ninety-eight ground surface temperature histories inverted from the temperature–depth borehole logs drilled on the territory of the Czech Republic [Bodri, L., ermák, V., 1995. Climate changes of the last millennium inferred from borehole temperatures: results from the Czech Republic — Part I. Global Planet. Change 11, pp. 111–125; Bodri, L., ermák, V., 1997. Climate changes of the last two millennia inferred from borehole temperatures: results from the Czech Republic — Part II. Global Planet. Change 14, pp. 163–173.] are used to reconstruct the regional patterns of the respective climate change. The climate was mapped for the following periods: 1100–1300 A.D. (Little Climatic Optimum), 1400–1500 A.D., 1600–1700 A.D. (main phase of the Little Ice Age), and for the most recent climate trend after year 1960. Comparison of the obtained maps with the meteorological observations and proxy climatic reconstructions confirmed good applicability of the “geothermal” paleoclimatic reconstructions for the regional studies.  相似文献   

7.
Geothermal observations from a suite of boreholes in western Utah, USA, combined with meteorologic data at nearby weather stations are used to test the hypothesis that temperatures in the earths subsurface contain an accurate record of recent climate change. The change in air temperature over the last hundred years successfully predicts detailed subsurface temperature profiles to better than ±0.05°C, indicating that ground temperatures tract air temperatures over long periods and that climate change signals are conducted into, and recorded in, the solid earth by the process of heat conduction. We combine borehole temperature data with meteorologic data from the nearest weather station to determine the time averaged difference between surface ground temperature and surface air temperature for borehole-weather station pairs and to infer the long term mean air temperature prior to the observational record. For our western Utah sites the preobservational mean temperature is close to the average surface air temperature for this century suggesting that up to 0.5°C of warming deduced from the last 100 years of weather station data may be attributed to recovery from a cool period at the turn of the century.  相似文献   

8.
Continuous temperature logs to depths between 750 and 1400 m in the Transylvanian Basin, Romania, in many cases show temperature gradient variations with depth which cannot be explained by depth variations in thermal conductivity, topography and ground water flow. The only possible responsible agent seems to be past surface temperature variations. The temperature logs from nine boreholes have been interpreted individually and jointly by least squares inverse modelling with the surface temperature history and background heat flux as unknown parameters. All the temperature profiles are consistent with a temperature rise at the end of the last glaciation. The effects of borehole depth, of a wrong choice of thermal conductivity, and the level of uncorrelated random noise were examined using synthetic examples.  相似文献   

9.
Several temperature-depth profiles measured in Kasai and in Shaba provinces of Zaire using mining exploration boreholes exhibit a significant negative temperature gradient near the surface. This anomalous curvature which extends to 100–200 m depth could reflect the effect of variations in surface conditions. Applying the theory of heat conduction in a semi-infinite homogeneous medium, these profiles indicate a surface warming by 3–4°C. This warming is related to the effect of the environmental changes associated with the mining exploitation and the urbanization during the last 40–90 years.  相似文献   

10.
Joint analysis of surface air temperature series recorded at weather stations together with the inversion of the temperature-depth profiles logged in the near-by boreholes enables an estimate of the conditions existing prior to the beginning of the meteorological observation, the so-called pre-observational mean (POM) temperature.Such analysis is based on the presumption of pure diffusive conditions in the underground. However, in real cases a certain subsurface fluid movement cannot be excluded and the measured temperature logs may contain an advective component. The paper addresses the correction for the hydraulic conditions, which may have perturbed the climate signal penetrating from the surface into the underground. The method accounts for vertical conductive and vertical advective heat transport in a 1-D horizontally layered stratum and provides a simultaneous evaluation of the POM-temperature together with the estimate of the Darcy fluid velocity. The correction strategy is illustrated on a synthetic example and its use is demonstrated on temperature logs measured in four closely spaced boreholes drilled near Tachlovice (located about 15 km SW of Prague, Czech Republic). The results revealed that in a case of moderately advectively affected subsurface conditions (fluid velocities about 10−9 m/s), the difference between POM-values assessed for a pure conductive approach and for combined vertical conductive/advective approach may amount up to 0.3–0.5 K, the value comparable with the amount usually ascribed to the 20th century climate warming.  相似文献   

11.
Functional space inversions (FSI) of precise temperature logs from wells located in low conductivity clastic sediments of the western Canadian Sedimentary Basin show evidence of extensive, recent ground surface temperature (GST) warming. Simultaneous inversion of the data, as well as averaging of the individual site reconstructions, indicate that this high magnitude of GST warming exceeds over two times that of globally averaged GST's [Science 282 (1998) 279] and is significantly higher than that of surface temperature histories based on instrumental records and tree ring reconstruction in northern and western Canada [Holocene 7 (1997) 375; Science 278 (1997) 1251; Clim. Res. 12 (1999) 39].  相似文献   

12.
We analyzed data from 23 boreholes at 19 sites in central and eastern Canada, for the purpose of estimating ground surface temperature (GST) histories. These boreholes were logged down to at least 550 m depth with thermistor probes. Thermal conductivity measurements had been previously made at small depth intervals for the entire depth ranges of most of the boreholes. The temperature profiles of these boreholes do not indicate water disturbance. We estimated terrain effects for each borehole using a time dependent solid-angle method. The thermal perturbations caused by lakes or deforestation near the borehole sites are insignificant in most cases. However, four of the holes were found to be severely influenced by terrain effects. GSTs estimated from the borehole data less influenced by the terraineffects form two groups. The first group, which are generally from data of better quality, show a cold period near the end of the last century before the recent warming trend; the second show it 80–100 years earlier. We consider the former typical of the climate of the Boreal climatic region of Canada. The difference between the two groups may reflect the spacial variability of the climate. Four GST estimates do not belong to either type, and the reasons are discussed.  相似文献   

13.
The occurrence of permafrost in bedrock in northern Fennoscandia and its dependence on past and presently ongoing climatic variations was investigated with one- (1D) and two-dimensional (2D) numerical models by solving the transient heat conduction equation with latent heat effects included. The study area is characterized by discontinuous permafrost occurrences such as palsa mires and local mountain permafrost. The ground temperature changes during the Holocene were constructed using climatic proxy data. This variation was used as a forcing function at the ground surface in the calculations. Several versions of the present ground temperature were applied, resulting in different subsurface freezing–thawing conditions in the past depending on the assumed porosity and geothermal conditions.Our results suggest that in high altitude areas with a cold climate (present mean annual ground temperature between 0°C and −3°C), there may have been considerable variations in permafrost thickness (ranging from 0 to 150 m), as well as periods of no permafrost at all. The higher is the porosity of bedrock filled with ice, the stronger is the retarding effect of permafrost against climatic variations.Two-dimensional models including topographic effects with altitude-dependent ground temperatures and slope orientation and inclination dependent solar radiation were applied to a case of mountain permafrost in Ylläs, western Finnish Lapland, where bedrock permafrost is known to occur in boreholes to a depth of about 60 m. Modelling suggests complicated changes in permafrost thickness with time as well as contrasting situations on southern and northern slopes of the mountain.Extrapolating the climatic warming of the last 200 years to the end of the next century when the anticipated increase in the annual average air temperature is expected to be about 2 K indicates that the permafrost occurrences in bedrock in northern Fennoscandia would be thawing rapidly in low-porosity formations. However, already a porosity of 5% filled with ice would retard the thawing considerably.  相似文献   

14.
Air and ground temperatures measured in Eastern Siberia has been compiled and analyzed. The analysis of mean annual air temperatures measured at 52 meteorological stations within and near the East-Siberian transect during the period from 1956 through 1990 demonstrates a significant and statistically significant (at 0.05 level) positive trend ranging from 0.065 to 0.59 °C/10 yr. A statistically significant (at 0.05 level) positive trend was also observed in mean annual ground temperatures for the same period. The permafrost temperature reflects changes in air temperature on a decadal time scale much better than on an interannual time scale. Generally, positive trends in mean annual ground temperatures are slightly smaller in comparison with trends in mean annual air temperatures, except for several sites where the discordance between the air and ground temperatures can be explained by the winter snow dynamics. The average trend for the entire region was 0.26 °C/10 yr for ground temperatures at 1.6 m depth and 0.29 °C/10 yr for the air temperatures. The most significant trends in mean annual air and ground temperatures were in the southern part of the transect, between 55° and 65° N. Numerical modeling of ground temperatures has been performed for Yakutsk and Tiksi for the last 70 yr. Comparing the results of these calculations with a similar time series obtained for Fairbanks and Barrow in Alaska shows that similar variations of ground temperatures took place at the same time periods in Yakutsk and Fairbanks, and in Tiksi and Barrow. The decadal and longer time scale fluctuations in permafrost temperatures were pronounced in both regions. The magnitudes of these fluctuations were on the order of a few degrees centigrade. The fluctuations of mean annual ground temperatures were coordinated in Fairbanks and Yakutsk, and in Barrow and Tiksi. However, the magnitude and timing of these fluctuations were slightly different for each of the sites.  相似文献   

15.
Permafrost warming in the Tien Shan Mountains, Central Asia   总被引：4，自引：0，他引：4  
The general features of alpine permafrost such as spatial distribution, temperatures, ice content, permafrost and active-layer thickness within the Tien Shan Mountains, Central Asia are described. The modern thermal state of permafrost reflects climatic processes during the twentieth century when the average rise in mean annual air temperature was 0.006–0.032 °C/yr for the different parts of the Tien Shan. Geothermal observations during the last 30 yr indicate an increase in permafrost temperatures from 0.3 °C up to 0.6 °C. At the same time, the average active-layer thickness increased by 23% in comparison to the early 1970s. The long-term records of air temperature and snow cover from the Tien Shan's high-mountain weather stations allow reconstruction of the thermal state of permafrost dynamics during the last century. The modeling estimation shows that the altitudinal lower boundary of permafrost distribution has shifted by about 150–200 m upward during the twentieth century. During the same period, the area of permafrost distribution within two river basins in the Northern Tien Shan decreased approximately by 18%. Both geothermal observations and modeling indicate more favorable conditions for permafrost occurrences and preservation in the coarse blocky material, where the ice-rich permafrost could still be stable even when the mean annual air temperatures exceeds 0 °C.  相似文献   

16.
Analysis and modelling of temperature anomalies from 25 selected deep wells in Alberta show that the differences between GST (ground surface temperature) warming for the northern Boreal Forest ecozone and the combined Prairie Grassland ecozone and Aspen Parkland transition region to the south occur during the latter half of this century. This corresponds with recent changes in surface albedo resulting from permanent land development in the northern areas and also to increases in natural forest fires in the past 20 years. Differences between GST and SAT (surface air temperature) warming are much higher in the Boreal Forest ecozone than in the Prairie Grassland ecozone and Aspen Parkland transition region. Various hypotheses which could account for the existing differences between the GST and SAT warming in the different ecozones of Alberta, and western Canada in general, are tested. Analysis of existing data on soil temperature, hydrological piezometric surfaces, snowfall and moisture patterns, and land clearing and forest fires, indicate that large areas of Alberta, characterised by anomalous GST warming, have experienced widespread changes to the surface landscape in this century. It is postulated that this has resulted in a lower surface albedo with a subsequent increase in the absorption of solar energy. Heat flow modelling shows that, after climatic SAT warming, permanent clearing of the land is the most effective and likely cause of the observed changes in the GST warming. The greater GST warming in the Boreal Forest ecozone in the latter half of this century is related to landscape change due to land development and increasing forest fire activity. It appears to account for a portion of the observed SAT warming in this region through a positive feedback loop with the overlying air. The anthropogenic effect on regional climatic warming through 20th century land clearing and landscape alteration requires further study. In future, more accurate quantification of these various forcings will be necessary in order to distinguish between, and to detect, the variety of natural and anthropogenic influences and on climate.  相似文献   

17.
Seasonal snow covers the tundra surface for up to nine months of each year on the Alaskan North Slope. Variations in the snow thickness could strongly influence the thermal regime of the underlying soil and permafrost, and the surface energy balance. The impacts of increases and decreases in the tundra snow thickness on the thermal regime of snow surface, active layer, and permafrost, and on the conductive heat flow to the atmosphere were investigated numerically, by using an improved surface energy balance approach based one-dimensional heat transfer model. The baseline inputs for the numerical model are mean daily meteorological data and surface albedos collected at Barrow, Alaska from 1995 through 1999. Based on a study for the long-term mean daily maximum and minimum snow thickness distributions at Barrow in the snow season of 1948 through 1997, a snow thickness factor was defined and five simulation cases were run for the snow season of 1997–1998 by changing the snow thickness factor. The modeled results indicate that changes in snow thickness have significant impacts on ground thermal regimes and conductive heat flow to the atmosphere. Decreasing the snow thickness by 50% led to the maximum ground temperature decrease of 1.48 °C at 0.29 m depth, and 0.72 °C at 3.0 m depth; the magnitude of the mean conductive heat flow to the atmosphere for December increase of 4.3 Wm− 2. Increasing the snow thickness by 50% resulted in the maximum ground temperature increase of 1.44 °C at 0.29 m depth, and 0.66 °C at 3.0 m depth; the magnitude of the mean conductive heat flow to the atmosphere for December decrease of 1.57 W m− 2. On an annual basis, variation in the snow thickness by 50%, the ground temperature variations of more than 0.25 °C occurred as deep as 8.0 m below the ground surface. The modeled results also show that changes in snow thickness have a relatively small influence on the snow surface temperature.  相似文献   

18.
This paper examines the cloud radiative forcing and its impacts on the surface climate for global climate model simulations that use reduced ozone concentrations and land fractions as boundary conditions. In one simulation using present-day land continents, ozone concentrations are reduced to zero and compared to the present-day climate simulation. In the second set of simulations under global ocean conditions, the implied poleward transport of heat by the ocean is varied. The removal of ozone causes an increase in longwave cloud radiative forcing at the top of the atmosphere and the surface. The increase in longwave forcing melts sea-ice and snow at high latitudes leading 10–14°C warmer temperatures and globally a 2°C increase. The global ocean simulations lead to higher cloud fractions than present-day simulation. Without poleward transport of heat by the ocean, surface temperatures cool as a result of higher cloud fractions. Increasing the ocean heat transport by a factor of 3.33 brings about ice-free conditions. An 11°C difference in globally averaged surface air temperatures is found between the enhanced and zero poleward oceanic heat transport simulations. The longwave cloud radiative forcing from high cloud fractions enhance the surface warming in the polar regions during the winter season. Conversely, during the summer season, a high cloud fraction increases the shortwave cloud radiative forcing producing only moderately warm temperatures in the polar regions. High cloud fractions in polar regions during warm periods throughout geologic times may help to explain the reduced equator to pole temperature gradient.  相似文献   

19.
An experimental air–ground climate station is operating in Pomquet, Nova Scotia, monitoring meteorological (surface air temperatures at three heights, wind velocity and direction, incoming solar radiation, precipitation, snow depth and relative humidity) and ground thermal variables (soil temperatures at depths of 0, 5, 10, 20, 50 and 100 cm). Readings are taken every 30 s and 5 min averages are stored, in order to characterize the energy exchanges at the air ground interface. Here, I report on the first year of operation. For spring, summer and fall, we find that soil temperatures track surface air temperatures with amplitude attenuation and phase lag with depth confirming that heat conduction adequately describe the soil thermal field at the Pomquet site. For winter conditions, we find that heat transfer is dominated by latent heat released during soil freezing and to a lesser extent by the insulating affect of snow cover. A numerical model of heat conduction was used in order to estimate the magnitude of the heat released by freezing during the winter months. I also show that there is an inverse correlation for the difference between soil (100 cm) and air temperatures and the incoming solar radiation at the site.  相似文献   

20.
In the western United States, more than 79 000 km2 has been converted to irrigated agriculture and urban areas. These changes have the potential to alter surface temperature by modifying the energy budget at the land–atmosphere interface. This study reports the seasonally varying temperature responses of four regional climate models (RCMs) – RSM, RegCM3, MM5-CLM3, and DRCM – to conversion of potential natural vegetation to modern land-cover and land-use over a 1-year period. Three of the RCMs supplemented soil moisture, producing large decreases in the August mean (− 1.4 to − 3.1 °C) and maximum (− 2.9 to − 6.1 °C) 2-m air temperatures where natural vegetation was converted to irrigated agriculture. Conversion to irrigated agriculture also resulted in large increases in relative humidity (9% to 36% absolute change). Modeled changes in the August minimum 2-m air temperature were not as pronounced or consistent across the models. Converting natural vegetation to urban land-cover produced less pronounced temperature effects in all models, with the magnitude of the effect dependent upon the preexisting vegetation type and urban parameterizations. Overall, the RCM results indicate that the temperature impacts of land-use change are most pronounced during the summer months, when surface heating is strongest and differences in surface soil moisture between irrigated land and natural vegetation are largest.  相似文献   

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