Ground Surface Warming History in Northern Canada Inferred from Inversions of Temperature Logs and Comparison with Other Proxy Climate Reconstructions

— Well temperature logs from 61 sites located in discontinuous and continuous permafrost regions of northern Canada are analyzed. The method of functional space inversion (FSI) is applied to the set of precise temperature logs from wells located between 60 ° and 82 °N. There is strong evidence of extensive ground surface temperature (GST) warming beginning in the late 18^th century and lasting until the 20^th century. This was preceded by a lengthy period of cooling. The approximate average increase of the surface temperature of Canadian Arctic, based on all individual GST histories, is > 1.3 °C for the last 200 years. Simultaneous inversion of all well temperature data suggests an even higher warming (approximately 2 °C). There has been no strong south-to-north gradient in the ground warming magnitude when northern Canadian data are compared with eastern and central Canadian data south of 60 °N which also shows warming close to 2 °C. In Alaska, warming of some 2 °C has been restricted mainly to the 20^th century. In general, however, a high warming magnitude is common for most of Canada and Alaska for the previous century. The averaged GST history (GSTH) for the Canadian Arctic is calibrated with and compares visually with a variety of recently published regional and hemispheric proxy climate reconstructions. These show that GST warming derived from well temperature logs is generally higher than one shown by other proxy (mainly tree-ring reconstructions).Received April, 2003     

Ground Surface Temperature History in Poland in the 16th–20th Centuries Derived from the Inversion of Geothermal Profiles

Ground Surface Temperature (GST) history in Poland was derived from the inversion of temperature-depth profiles in over 20 wells. Temperature histories for the period 1500 A.D. through 1977 A.D. agree well with the instrumental record of the surface-air temperature available for the last two centuries. A statistical correlation of the reconstructed histories (from the well temperature data) with the instrumental record (air temperature) from the homogeneous Warsaw series is high (>0.8). Functional space inversion (FSI) of the temperature data with depth shows that beginning in the early 19th century, temperatures warmed by 0.9 ± 0.1°C following a long period of colder climate before. The last number could be a minimal as higher warming was calculated using a simple model based on surface temperature for the observational period (homogenized Warsaw surface temperature series, Lorenc, 2000) and POM (pre-observational mean; Harris and Chapman, 1998) of –1.53^oC below the 1951–1980 mean temperature level.     

CLIMATE HISTORY INFERRED FROM BOREHOLE TEMPERATURES, DATA FROM THE CZECH REPUBLIC

The knowledge of the present-day underground temperatures may be important in the assessments of the past climate change. The method of inversion of the temperature-depth records into the ground surface temperature history is briefly introduced by showing an example of synthetic data and illustrated by a review of existing results obtained from the inversion of temperature logs measured in holes in the Czech Republic. Underground temperatures observed in holes of the depth of at least 1000–1500 m seem to confirm the preinstrumental climate pattern of the past several thousand years. Most of shallower temperature records (500–800 m) revealed general warming of climate followed the Little Ice Age of the 17–18th centuries and a pronounced increase of the soil temperatures by at least 1 K since the beginning of this century.     

Inference of ground surface temperature history from subsurface temperature data: Interpreting ensembles of borehole logs

Ground surface temperature histories (GSTHs) inferred from borehole temperaturedepth (T-z) data are often degraded, to a various extent, by random or systematic noise in theT-z data and in the measurements of thermophysical properties of the earth. To minimize the effects of noise, and hence improve the fidelity of the inferred GSTH, a plausible approach is to perform a simultaneous inversion, of theT-z logs in a region, or alternatively, to invert the individualT-z logs and then average the resulting GSTHs. Averaging and simultaneous inversion are conceptually different: whereas an averaging can always be peformed, a simultaneous inversion is predicated on the assumption of a common transient component of the GSTH in all theT-z logs. In this work we examine and compare the two approaches, using a time domain inverse formulation based on the method of least squares. We consider a set of scenarios: (a) multipleT-z logs from a single borehole, (b) multiple boreholes from a single site, (c) multiple boreholes in similar climatological settings, and (d) multiple boreholes in different climatological settings. We show that for (a), (b) and (c), averaging and simultaneous inversion yield nearly identical results. For boreholes in different settings, the assumption of a common transient GSTH may be invalid and averaging and simultaneous inversion give divergent results.     

Climate change inferred from analysis of borehole temperatures: First results from Alberta Basin,Canada

High quality temperature measurements have been made to depths of 30 to 220 m at 42 sites in 62 observational hydrogeological wells in Alberta. The temperature profiles commonly show near-surface inversions with a minimum temperature at depths of 30 to 50 m. Thermal modelling suggests a surface temperature history with warming reaching 2°C over the past 30 to 60 years. Recent climate warming evident from the analysis of the air temperature data in the region seems to provide at least a partial explanation of the increased ground temperatures. A sudden increase of the surface ground temperature caused by land clearing may be the other explanation, although modelling of such a sudden increase can only explain the observed temperature-depth data if the onset of such warming is 20–30 years old, which is in disagreement with the history of land development in the studied area. The effect of near-surface inversions of the temperature profiles also has been observed in the forested areas. The above support the climate based effect. The superposition of the climatic effect and man-made activity effect upon the ground warming is a very complicated process calling for considerably more research.     

Long-term trends and regime shifts in sea surface temperature on the continental shelf of the northeast United States

We investigated sea surface temperature (SST) variability over large spatial and temporal scales for the continental shelf region located off the northeast coast of the United States between Cape Hatteras, North Carolina, and the Gulf of Maine using the extended reconstruction sea surface temperature (ERSST) dataset. The ERSST dataset consists of 2°×2° (latitude and longitude) monthly mean values computed from in situ data derived from the International Comprehensive Ocean Atmosphere Data Set (ICOADS). Nineteen 2°×2° bins were chosen that cover the shelf region of interest between the years of 1854 and 2005. Mean annual and range of SST were examined using dynamic factor analysis to estimate trends in both parameters, while chronological clustering was used to determine temporal SST patterns and breakpoints in the time series that are believed to signal regime shifts in SST. Both SST and SST trend analysis show that interannual variability of SST fluctuations shows strong coherence between bins, with declining SST at the beginning of the last century, followed by increasing SST through 1950, and then rapidly decreasing between 1950 and mid-1960s, with somewhat warmer SST thereafter to present. Annual SST range decreases in a seaward direction for all bins, with strong coherence for interannual variability of range fluctuations between bins. The trend in SST range shows a decreasing range at the beginning of the last century followed by an increase in range from 1920 to the late-1980s, remaining high through present with some spatial variability. A more detailed spatial analysis was conducted by grouping the data into 7 regions using principal component analysis. We analyzed regional trends in mean annual SST, seasonal SST range (summer SST−winter SST), and normalized SST minima and maxima. Both the summer and winter seasons were also analyzed using the length of each season and amplitude of the warming and cooling season, respectively, along with the spring warming and fall cooling rates. Trends in all of the parameters were examined after low-pass filtering using a 10-point convolution filter (n=10 years) and regime shifts were identified using the sequential t-test analysis of regime shifts (STARS) method. The analysis shows some difference between regions in the timing of minimum SST with minima being reached 1 month earlier in the south (February) relative to more northern regions (March). Regional annual SST range decreased in a seaward direction. Amplitude of summer warming and the length of summer have shown fluctuations with recent years showing stronger warming and longer summers but generally not exceeding past levels. Overall, the difference in SST range, with recent larger values may be the most significant finding of this work. SST range changes have the potential to disrupt species important to local fisheries due to combinations of differing temperature tolerances, changes in reproduction potential, and changes in the distributional range of species.     

Mid-latitude atmospheres,winter and summer

Summary Winter and summer Mid-Latitude (45^oN) atmospheres to 90 km, two of a family of nine atmospheres supplemental to the U.S. Standard Atmosphere (1962), provide information on atmospheric structure by seasons rather than the mean annual data shown in the Standard, which is described for reference. Principal data sources for constructing these atmospheres consisted of summaries of Northern Hemisphere radiosonde observations at stations near, 45^oN, and observations made from rockets and instruments released by rockets, from nearly a dozen Northern Hemisphere launching sites.Winter and summer temperature-height profiles begin with surface temperatures of –1° and +21 °C, respectively, and contain three isothermal layers: –58°C at 19 to 27 km in winter and –57.5°C at 13 to 17 km in summer; –7.5° and +2.5°C at 47 to 52 km; and –79.5 and –99°C at 80 to 90 km, respectively. The temperature-height curve for the U.S. Standard has a surface temperature of +15°C with isothermal regions at 11 to 20 km (–56.5°C), 47 to 52 km (–2.5°C), and 80 to 90 km (–92.5°C). In all three atmospheres, temperature gradients for various segments are linear with geopotential, height. Humidity is incorporated into the lowest 10 km of the Supplemental Atmospheres, whereas the Standard is dry. Figures and tables depict temperature, relative humidity, pressure, and density for winter and summer, and temperature, pressure, density, speed of sound, and dynamic viscosity for the U.S. Standard Atmosphere.The Supplemental Atmospheres are mutually consistent; zonal wind profiles, computed from the geostrophic wind equation and selected pressure heights, compare favorably with existing radiosonde and rocket wind observations.     

Pre-Observational Evolution of Surface Temperature in Romania as Inferred from Borehole Temperature Measurements

Temperature data from nine boreholes in the Carpathian orogen in Romania were used to obtain information on the ground surface temperature history (GSTH) in the last 250?years. The temperature measurements were taken with a thermistor probe (sensitivity in the 10 mK range) using the stop-and-go technique, at 10 m intervals, in the depth range of 20–580?m. The least squares inverse modelling approach of Tarantola and Valette (J Geophys 50:159–170, 1982) was used to infer the GSTH. Long-term air temperature records available from the Romanian weather station network were used as a comparison term for the first 100–150?years of the GSTH, and as a forcing function in a POM-SAT model that combines borehole temperature profiles (BTPs) and meteorological time series (surface air temperature, SAT) to produce information on the so-called pre-observational mean (POM). Results from a global circulation model for the Romanian area are incorporated in the discussion as well.     

The influence of global warming in Earth rotation speed

The tendency of the atmospheric angular momentum (AAM) is investigated using a 49-year set of monthly AAM data for the period January 1949–December 1997. This data set is constructed with zonal wind values from the reanalyses of NCEP/NCAR, used in conjunction with a variety of operationally produced AAM time series with different independent sources and lengths over 1976–1997. In all the analyzed AAM series the linear trend is found to be positive. Since the angular momentum of the atmosphere–earth system is conserved this corresponds to a net loss of angular momentum by the solid earth, therefore decreasing the Earth rotation speed and increasing the length of day (LOD). The AAM rise is significant to the budget of angular momentum of the global atmosphere–earth system; its value in milliseconds/century (ms/cy) is +0.56 ms/cy, corresponding to one-third of the estimated increase in LOD (+1.7 ms/cy). The major contribution to this secular trend in AAM comes from the equatorial Tropopause. This is consistent with results from a previous study using a simplified aqua-planet model to investigate the AAM variations due to near equatorial warming conditions. During the same time interval, 1949–1997, the global marine + land-surface tempera- ture increases by about 0.79 °C/cy, showing a linear correspondence between surface temperature increase and global AAM of about 0.07 ms per 0.1 °C. These results imply that atmospheric angular momentum may be used as an independent index of the global atmosphere’s dynamical response to the greenhouse forcing, and as such, the length of day may be used as an indirect indicator of global warming.     

Reconstruction of the surface temperature in the Kura depression (Azerbaijan) by the inversion of borehole data

In order to reconstruct the ground surface temperature history (GSTH) in the Kura depression from the data on borehole temperatures, we selected two thermal logs, which met the requirements of the well temperature inversion into the GSTH. The temperature gradients measured in these wells varied about 20 K/km, which is typical for the region of study. The borehole temperatures were inverted into the ground surface temperatures in the past in accordance with the program developed by Po Yu Shen. It was found that the ground surface temperature had increased by 1–2°C during the last century. The GSTH derived from the well temperature inversion agrees with the climate temperatures measured at the Ganca meteorological station, which has been operating since 1873. These results obtained for the Kura depression are consistent also with the results of similar studies in other regions in the world.     

Paleomagnetic constraints on eruption patterns at the Pacaya composite volcano,Guatemala

Pacaya volcano is an active composite volcano located in the volcanic highlands of Guatemala about 40 km south of Guatemala City. Volcanism at Pacaya alternates between Strombolian and Vulcanian, and during the past five years there has been a marked increase in the violence of eruptions. The volcano is composed principally of basalt flows interbedded with thin scoria fall units, several pyroclastic surge beds, and at least one welded tuff. Between 400 and 2000 years BP the W-SW sector of the volcano collapsed producing a horseshoeshaped amphitheater (0.65 km³) and providing a window into the cone's infrastructure. Lava flows and tephra exposed in the amphitheater are more then 200 m thick and when combined with flows erupted recently represent between 30 and 40% of the cone's history. Pacaya is ideally suited for a paleomagnetic study into the timing and duration of eruption episodes at a large, composite volcano. We drilled 27 paleomagnetic sites (25 aa flows, 1 dike, and 1 welded tuff) from four lava-flow sequences with between 4 and 14 sites per sequence. The four sequences represent initial through historic activity at Pacaya. We resolved, what appear to be, 22 time-independent paleomagnetic sites by averaging together directions from successive sites where the sitemean directions were indistinguishable at the 95% level of confidence. However, mean-sequence directions of individual lava-flow sequences yielded unusually high Fisher precision parameters (k=44–224) and small circles of 63% confidence (a₆₃=1.6–6.1°) suggesting as few as three or four time-independent sites were collected. This indicates that activity as Pacaya is strongly episodic and that episodes are characterized by voluminous outpouring of lavas. Modelling the data using Holocene PSV rates confirms this and shows that differences in within-sequence directions (6–11.5°) are consistent with emplacement of lava-flow sequences in less than 100 years to as many as 300 years. Relatively larger differences in directions (18–23°) between subjacent lava-flow sequences indicates that repose is at least 300–500 years and could be even longer.     

Recent Climate Warming: Surface Air Temperature Series and Geothermal Evidence

Long-term (1961 – 1996) meteorological air temperature series together with the reconstructed ground surface temperature histories, obtained by inverting borehole temperature-depth profiles, were used to project regional patterns of the recent (climate) warming rate on the territory of the Czech Republic. The characteristic magnitude of the warming rate of 0.02 –0.03 K/yr was confirmed by the results of several years of monitoring the temperature in two experimental boreholes. The monitoring of shallow temperatures at depths of about 30 –40 m, i.e. below the reach of the seasonal surface temperature variations, can serve as an alternative tool of direct quantitative assessment of the present warming rate. The data also seem to sustain a potential man-made component contributing to the more pronounced recent warming rate observed in the areas of large agglomeration.     

Changes of Ozone Content at Middle Latitudes During Forbush Decreases in Cosmic Rays

The variations of total ozone at Alma-Ata (43°N, 76 °E) and ozone profiles obtained by balloon sounding at Tateno (36°N, 140°E), Wallops Island (38°N, 75°W) and Cagliari (39°N, 9°E) in the periods of Forbush decreases (FD) in galactic cosmic rays have been analysed. A decrease of total ozone was observed in the initial stage of the FD and an increase 10–11 days later. The average total deviations calculated using the superposed epoch method for 9 FD events are equal to 30 D. U. in the positive and to –18 D. U. in the negative phase. The changes of average ozone profiles, associated with 26 FD events, are more significant in the lower stratosphere and upper troposphere. The decrease of the partial ozone pressure at a height of 12–15 km is about 30 mb. These vertical variations of ozone coincide with the average changes of the respective temperature profiles. A cooling, on the average, of 3°C was observed at 12–15 km, and a heating of 4°C below this level.     

Temperature dependence of thermal conductivity and its impact on assessments of heat flux

The variability of sedimentary thermal conductivities with increasing temperature are explored for their impact on estimates of present-day heat flux and subsurface temperature gradient. For sand thicknesses less than about 10–20 km, or shale thicknesses less than about 40–80 km, the subsurface temperature is closely linearly proportional to the thermal resistance integral obtained in the absence of the temperature dependence of thermal conductivity. Estimates of heat flux should be increased (decreased) by about 5% for sands and decreased by about 1% for shales. For salt, because of the much shorter temperature range over which its thermal conductivity decreases, effects produced by the temperature dependence are more noticeable: heat flux should be increased by around 13%, salt thicknesses in excess of 5 km will yield major (around 30–100°C) changes in their temperature regimes solely as a consequence of the temperature-dependent thermal conductivity, and the linear increase of temperature with increasing thermal resistance is not an adequate approximation but has to be replaced with a more exact exponential increase.The impact of the variations, particularly in the case of salt, for geologic processes is briefly considered.     

Changes in the thermal structure of moderate to large sized lakes in response to changes in air temperature

Interannual variability in the thermal structure of lakes is driven by interannual differences in meteorological conditions. Dynamic or mechanistic models and empirical or statistical methods have been used to integrate the physical processes in lakes enabling the response of the thermal structure to changes in air temperature to be determined. Water temperature records for Lake Mendota, WI., are possibly the most extensive for any dimictic lake in the world and allowed both approaches to be used. Results from both techniques suggest the mixed layer temperature increases with increasing air temperature. Results from the empirical approach suggested epilimnion temperatures increase 0.5 to 1.0°C per 1.0°C increase in air temperature compared to 0.4 to 0.85°C estimated from a dynamical model (DYRESM). Increased air temperatures are related to significant warming in deep water temperatures in the absence of stratification; however, mid summer hypolimnion temperatures are expected to change very little or increase only slightly in response to climatic warming. Both approaches suggest increases in air temperatures increase the length of summer stratification; results from the dynamic model suggest an increase of approximately 5 days per 1°C increase in air temperature. Longer stratification is reflected in shallower late summer thermocline depths. With these quantitative relationships and forecast increases in air temperature for the 2 × CO₂ climatic scenario (Greenhouse Effect) from three General Circulation Models, projections are made describing the changes in the future mean thermal structure of moderate to large sized lakes.     

A note on some early radiosonde temperature observations in the Antarctic lower stratosphere

The behaviour of the Southern Hemisphere stratosphere has attracted considerable interest, and been compared with the Northern Hemisphere, since the International Geophysical Year (1957–58) when the sudden (explosive or accelerated) springtime warming phenomenon in the Antarctic was first observed. Over the years studies of upper air temperature and wind observations have been made, principally through the spring months when the polar vortex breakdown occurs, utilising both ground-based (rawinsonde, rocket) and more recently, satellite-derived data. Although the radiosonde-derived temperature data are limited both by the number of reporting stations, and the practical difficulty of securing observations much above the 100 hPa level, useful records exist from 1956 or 1957. These have shown that in the 1959 southern spring, the lower stratosphere was relatively colder, and the warming rate through the season was essentially more regular, with little evidence of the marked but short-lived temperature fluctuations usually found. Similar, but not quite such wide-spread conditions occurred again in the 1961 spring. In another study, 30 hPa temperature fields over the Antarctic continent, which could be drawn for the 1967 spring, showed the complexity of the polar vortex breakdown. These features are recalled because extension of the 100 hPa springtime temperature series for the Australian Antarctic station at Casey (66.3°S, 110.5°E) shows that in 1985 and part of 1986, the temperature behaviour there was similar to, but not quite so extreme as that which occurred at Mirny (66.5°S, 93.0°E) in 1959.     

Ground surface temperature history in southern Canada: Temperatures at the base of the Laurentide ice sheet and during the Holocene

We use temperature profiles from 7 deep (≈ 2000 m) boreholes located in southern Canada to infer ground surface temperature histories (GSTH) during the Last Glacial Maximum (LGM) and the Holocene. Visual inspection of the heat flow and of the reduced temperature depth profiles reveals significant regional differences with some sites showing conspicuous signs of post glacial warming, and other indicating only very small changes in ground surface temperature. These differences are confirmed by the inversions of the temperature profiles. The most prominent variations in GST are found at the Sudbury, Ontario, sites where the present ground surface temperature is high. With the exception of Sept-Iles, Quebec, the other sites only show moderate or no variation in GST. For all the sites, except possibly Sept-Iles, temperatures at the base of the ice sheet during the LGM were at or slightly below the melting point of ice. Temperatures might have been lower, a few degrees below 0 °C, at Sept-Iles. These results are consistent with field observations and model predictions suggesting high velocity basal flows in the ice sheet above the studied regions. These new data on basal temperatures will provide better quantitative constraints on glacier flow dynamics. The inversions give a chronology for the retreat of the ice sheet comparable to other proxies. Inversion and direct modeling show that, following the ice retreat, there was a warm period between 2 and 5 ka with temperatures 1–2 K higher than present. The inversion yields a time for this episode 1–2 kyr more recent than that inferred by other proxies for the Holocene climate optimum (HCO).     

Ice sheets and the CO2 problem

In this review, the carbon dioxide problem is discussed, with special reference to the possible effects of a global warming on the ice sheets of Greenland and Antarctica. Instead of detailed projections of future climate and the consequences, the basic mechanisms are explained and illustrated with results described in the literature.It is concluded that a doubling of the atmospheric CO₂ content (most likely to occur somewhere in the second half of the next century) will result in a globally-averaged warming of 2–4°C, and an intensification of the hydrological cycle. In the polar regions, this warming will be a few degrees larger and as a consequence the Greenland Ice Sheet will decrease in size. Antarctica, on the other hand, is expected to grow because of the increased snowfall. The instability of the West Antarctic Ice Sheet is also discussed and, although no conclusive prediction to its long-term response can be made, it is argued that on a short time scale (less than about 100 y) nothing dramatically wil happen to this part of Antarctica.     

Upper mixed layer temperature anomalies at the North Atlantic storm-track zone

Synoptic sea surface temperature anomalies (SSTAs) were determined as a result of separation of time scales smaller than 183 days. The SSTAs were investigated using daily data of ocean weather station “C” (52.75°N; 35.5°W) from 1 January 1976 to 31 December 1980 (1827 days). There were 47 positive and 50 negative significant SSTAs (lifetime longer than 3 days, absolute value greater than 0.10 °C) with four main intervals of the lifetime repetitions: 1. 4–7 days (45% of all cases), 2. 9–13 days (20-25%), 3. 14–18 days (10-15%), and 4. 21–30 days (10-15%) and with a magnitude 1.5-2.0 °C. An upper layer balance model based on equations for temperature, salinity, mechanical energy (with advanced parametrization), state (density), and drift currents was used to simulate SSTA. The original method of modelling taking into account the mean observed temperature profiles proved to be very stable. The model SSTAs are in a good agreement with the observed amplitudes and phases of synoptic SSTAs during all 5 years. Surface heat flux anomalies are the main source of SSTAs. The influence of anomalous drift heat advection is about 30-50% of the SSTA, and the influence of salinity anomalies is about 10-25% and less. The influence of a large-scale ocean front was isolated only once in February-April 1978 during all 5 years. Synoptic SSTAs develop just in the upper half of the homogeneous layer at each winter. We suggest that there are two main causes of such active sublayer formation: 1. surface heat flux in the warm sectors of cyclones and 2. predominant heat transport by ocean currents from the south. All frequency functions of the ocean temperature synoptic response to heat and momentum surface fluxes are of integral character (red noise), though there is strong resonance with 20-days period of wind-driven horizontal heat advection with mixed layer temperature; there are some other peculiarities on the time scales from 5.5 to 13 days. Observed and modelled frequency functions seem to be in good agreement.     

Temperature profiles in the earth of importance to deep electrical conductivity models

Deep in the Earth, the electrical conductivity of geological material is extremely dependent on temperature. The knowledge of temperature is thus essential for any interpretation of magnetotelluric data in projecting lithospheric structural models. The measured values of the terrestrial heat flow, radiogenic heat production and thermal conductivity of rocks allow the extrapolation of surface observations to a greater depth and the calculation of the temperature field within the lithosphere. Various methods of deep temperature calculations are presented and discussed. Characteristic geotherms are proposed for major tectonic provinces of Europe and it is shown that the existing temperatures on the crust-upper mantle boundary may vary in a broad interval of 350–1,000°C. The present work is completed with a survey of the temperature dependence of electrical conductivity for selected crustal and upper mantle rocks within the interval 200–1,000°C. It is shown how the knowledge of the temperature field can be used in the evaluation of the deep electrical conductivity pattern by converting the conductivity-versustemperature data into the conductivity-versus-depth data.