Observations of northern latitude ground-surface and surface-air
Transcript of Observations of northern latitude ground-surface and surface-air
Observations of northern latitude ground-surface
and surface-air temperatures
Allan D. Woodbury†, AKM H. Bhuiyan‡ and John Hanesiak ‡
†
Department of Civil Engineering, University of Manitoba, Winnipeg, Manitoba, R3T
5V6, Canada.
‡ Center for Earth Observation and Science (CEOS), Faculty of Environment, Earth,
and Resources, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
Abstract.
Since Lachenbruch and Marshall’s classic study of subsurface temperatures in
Alaska, there has been a great deal of interest in studying climate change through
reconstructing ground surface temperatures (GST) from borehole measurements
(BHT). Note that the magnitude of temperature increases reconstructed from BHT
records seems to contrast however, with some proxy based reconstructions of surface
air temperature (SAT) that indicate lower amounts of warming over the same period.
We present data suggesting that seasonal snowcover may bias climate reconstructions
based on BHT in portions of the Canadian northwest. Eight sites west of the Canadian
cordillera, were examined for long-term SAT and GST changes. At seven of these
sites precise borehole temperature profiles are used for the first time since the 1960s,
thereby exploring the linkage between GST and SAT. New readings were made at
four of these locations. All sites showed significant increasing SAT trends, in terms
of annual mean minimum and maximum temperatures. Over a 54 year period,
the minimum temperatures increased between 1.1o C and 1.5o while the maximum
increased between 0.8o C and 1.5o C, among those eight stations. Observations of
GST at those sites, however, showed no obvious climate induced perturbations. We
believe this disconnect between SAT and GST is attributable to an increase in snow
cover in early winter, followed by an increasing trend toward earlier snow melt in the
region. Such seasonal bias has important implications for GST reconstructions based
on borehole temperatures. These results support Mann and Schmidt’s conjecture about
a seasonal bias in the GST reconstructions from borehole surveys and counter assertions
of lower historic earth temperatures.
c©Allan D. Woodbury, Hassan Bhuiyan and John Hanesiak, 2007. Sumitted to Env.
Res. Let., December 2007.
† Corresponding address: E1-314 Engineering building, Department of Civil Engineering, University
of Manitoba, 15 Gillson Street, Winnipeg, Manitoba, R3T 5V6, Canada. ([email protected])
Northern latitude ground-surface-air temperatures 2
1. Introduction
The effects of climatic variations on subsurface temperatures have been known for some
time (Lane, 1923; Birch, 1948). However, it was not until Lachenbruch and Marshall’s
(1986) study of subsurface temperatures in Alaska was it realized that subsurface
temperatures could provide information on changes in climate over the last few centuries.
Since this time there has been a great deal of interest in using subsurface temperatures
to study climate change through reconstructing ground surface temperatures (GST;
for example, Harris and Chapman, 1997; Beltrami and Harris, 2001). Atmospheric
scientists are now beginning to explore the possibilities of using borehole temperatures
(BHT) as a source of data for the purposes of improving global circulation models, and
equally important for verifying the land surface schemes that are embedded in GCMs.
The GST reconstructions require the application of the theory of one-dimensional
heat conduction; the physics of which is well understood (Carslaw and Jaeger, 1959;
Jessop, 1990). However, the reconstructions are not the actual surface air temperatures
(SAT); the connection between them is a subject of active research (e.g. Schmidt et al.,
2001; Beltrami, 2001; Beltrami et al., 2005). Recent works (for example, see Beltrami
et al., 2005) have suggested that borehole GSTs are, in fact, robust reflections of past
climates.
Our understanding of the coupling between GSTs and surface air temperatures
(SAT) has improved. Subsurface temperature changes may result from factors other
than climate change and these are numerous: snow cover, changes in albedo, forest floor
organic layer thickness, and evapotranspiration, amongst other factors. For example,
studies have shown the effects on subsurface heat transfer from deforestation (Nitoiu
and Beltrami, 2005). Ferguson and Beltrami (2006) examined this issue in some detail
with numerical modeling. In their study, temperature anomalies associated with two-
dimensional (lateral) heat flow were evaluated for different scales of land-use. Changes
of land-use over large areas does indeed cause significant, but local changes in downhole
temperatures beyond the extent of the affected area. Their guidelines suggest that for
surface clearings of 500 m radius, borehole temperature measurements should be made
at least 60 m from the edge of an anomaly.
It is apparent that the issues related to deforestation are part of a larger issue of
how changes in the land surface affects sub-surface temperature and rates of climate
change predicted from BHTs. According to Beltrami et al (2003) and Majorowicz and
Safanda (2005) there were large areas of eastern and central Canada that experienced
warming in the 19th century but there were also large areas of Western Canada that had
no change or even cooled (based on borehole reconstructions). These authors conclude
that climatic warming is the main forcing, but land use changes from deforestation or
conversion of grasslands over to agricultural lands can affect the surface and therefore the
subsurface temperatures. The instrumental (SAT) record is clear though, and identifies
the greatest global warming occurring in the 20th century and in Canada this was
experienced in western Canada, but typically east of the Cordillera (Zhang et al., 2000).
Northern latitude ground-surface-air temperatures 3
Some have suggested that warming of the ground surface has not occurred. Lewis et al.
(2003) for example, concluded that
“ In the Canadian Cordillera universal warming at the ground surface due
to climate change over the past two centuries and subsequent propagation of
temperature anomalies down to 100 - 200 m depth has not occurred ... as it
has in central and eastern Canada.”
However, Lewis et al. (2003) cite the work of Lewis and Wang (1998) who focused
on disturbances in Vancouver Island, much further to the south of the northern sites
quoted in Lewis et al. (2003). Therefore, other than the boreholes themselves, there
were no other independent data to support the conjectures noted above.
In this paper, eight sites in north-western Canada, west of the Cordillera, are
examined for long-term SAT changes (Figure 1). The selected stations are: (a) White
Horse (60o 45.0’N, 135o 11.0’ W), (b) Ruby Creek (59o 42.8’ N,133o 24.1’ W), (c) Dease
Lake (58o 38.9’N,130o 0.6’W), (d) Hotailuh (58o 9.6’N,129o 51.9’W), (e) Gnat Lake
(58o 15.3’ N,129o 49.0’W), (f) Buckley Lake (57o 53.6’ N,130o 51.3’W), (g) Stikine
Site Z (58o 6.0’ N ,130o 16’W), and (r) Ritchie (56o 25.1’ N ,129o 0.92’W). At seven
of these sites precise temperature profiles observed in the 1960’s - 1970’s are used to
explore the linkage between GSTs and SATs. The borehole logs and their descriptions
were obtained from the the Geological Survey of Canada’s repository of temperature
recordings. We attempt to link the results of new readings at four sites taken in 2006
with those previously, and also to the instrumental atmospheric records for observation
and interpretation. The exciting part of this analysis is that at all of the sites we looked
at very little land use changes have occurred for over 25 years.
Long term trends in monthly average maximum and minimum temperatures are
investigated using the adjusted Canadian gridded (CANGRID) dataset (Zhang et al.,
2000) for the eight stations. Two different time series are considered (1950 to 1998 and
1950 to 2003) for long term trend analysis. Seasonal trends (Winter -Dec to Feb, Spring
- Mar to May, Summer - Jun to Aug, Autumn - Sep to Nov) are also analyzed using
same time series.
2. Atmospheric Temperature Trend Analysis
The CANGRID dataset contains monthly temperature and precipitation that covers
Canada. The CANGRID data are adjusted using surrounding stations to ensure
homogeneous time series and corrected for bias due to observational system change,
station relocation and so on. The data grid is a polar stereographic projection with a 50
km spatial resolution. The grid is a 125 (columns) by 95 (rows) matrix. Further details
of CANGRID data can be found in Zhang et al. (2000).
The nearest CANGRID data point to each station was used for the atmospheric
temperature trend analysis (see Zhang et al., 2000). The statistical model initially
removes the autocorrelation from the time series, then the slope (the linear regression
Northern latitude ground-surface-air temperatures 4
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Figure 1. North West Canada Observation sites
between climate variable and time) and its significance level are obtained from the de-
autocorrelated time series. The estimated slope is then used to remove the trend from
the original series and resulting residuals are used to obtain a more accurate estimation
of the (lag - 1) autocorrelation. To determine the statistical significance of the trend,
the confidence interval for the slope is obtained in terms of lower and upper bounds
based on the order of all possible slopes (Zhang et al., 2000).
During the study we used Zhang et al. (2000)’s model to calculate lower and
upper bound of slope, and Z-statistics for maximum and minimum temperature for
our selected stations extracted from the CANGRID time series (1950 to 2003), and
results are presented in Tables 1 to 5 and temperature plots corresponding to mean
annual maximum and minimum temperatures are shown in Figures 8 and 9. A linear
regression line is also plotted on each figure along with the terms in the equation.
All eight sites show a statistically significant increasing trend, > 95% in most
cases, in annual mean minimum and maximum temperatures (Table 1). Over the 54
year period, the increase in minimum temperatures has been between 1.1oC and 1.5o
and the increase in maximum temperatures has ranged between 0.8C and 1.5C over the
eight stations. All stations, except for White Horse, have larger increases in minimum
temperatures compared to maximum temperatures, which is consistent with Zhang et al
(2000). Tables 2 - 5 suggest that the annual mean trends are significantly influenced by
winter (DJF) and spring (MAM) temperature trends as opposed to summer (JJA) and
autumn (SON). Mean annual winter minimum temperature trends range between 2o
and 4o over the 54 year period, while mean annual winter maximum temperature trends
range over 1.9o to 4.2o, all being statistically significant to > 90% confidence. Once
Northern latitude ground-surface-air temperatures 5
again, the minimum temperature trends tend to be slightly larger than the maximum
temperature trends at most stations. The spring temperature trends (Table 3) are much
smaller than the winter trends (Table 2), however, spring trends still remain all positive
with most of them statistically significant at the 90% level. Tables 4 and 5 indicate that
summer and autumn do not have any statistically significant temperature trends since
all confidence levels are less than 80%, with most of them much lower than this (not
indicated in the tables).
3. Borehole Measurement Techniques
Temperature recordings were made using standard analog techniques, but with devices
specifically adapted for northern Canadian use. Many of the sites are only accessible
by helicopter. Temperatures were measured with a portable winch and a resistance
temperature detector (RTD). The temperature sensor is a 100 ohm OMEGATM platinum
resistance element in a 3 mm probe tip. The present implementation includes a 300 m,
5.5 mm diameter kevlar strengthened cable. We used a four wire connection to the RTD,
with the data taken with a specially designed readout box (essentially a Wheatstone
bridge). The probe is 1.9 cm outside diameter and has been used in 2.54 cm boreholes.
The overall accuracy ( ±0.01o C) is controlled by precise calibration in a thermal bath
and was confirmed by comparison to a SEABIRDTM digital-platinum RTD. Field data
were recorded the summer of 2006.
The earlier GSC data (and the sites) were described by Jessop et al. (1984).
Temperature recordings were made at various times, but typically in the mid 1960s
to early 1970’s. Temperatures for this earlier GSC work were also measured with a
portable winch and a thermistor sensor. Jessop et al (1984) report accuracies of ±0.02o
C. Detailed comments on each site, as originally described by Jessop et al. (1984), are
given below.
In the majority of the observed sites presented below synthetic temperature-depth
profiles are also plotted. These theoretical responses are calculated by assuming a series
of linear changes of the surface temperature. The pattern consisted of an average GST
increase between 1800 and 1900 of 0.44 C and 0.71 C from 1900 to 1950, followed by
another linear increase based on the SAT records at each site noted in Table I (see
Beltrami et al., 2003). The temperature at surface is assumed constant before 1800. At
each site, this synthetic GST history is used as the driving signal for computation of
the theoretical temperature at depth (at an appropriate time) and is combined with a
linear slope and intercept determined from linear regression of portions of each borehole
temperature record. A homogeneous value of thermal diffusivity of 1.2 × 10−6 m2/sec
was used. If the conceptual model of the earth response is correct; namely a purely 1-D
conductive environment, then the observed borehole temperatures should be reflective
of a subsequent temperature propagation from surface. If not, then some mechanism
must be responsible for removal of the energy that is available from an overall warming
at each site.
Northern latitude ground-surface-air temperatures 6
3.1. Whitehorse
Measurements were originally obtained in a mineral exploration hole drilled by
Whitehorse Copper Mines Ltd. about 5 km west of the city of Whitehorse. The
geology at the site consists of grandioritic batholith, and the hole was drilled 388 m
at an inclination of 60o. The area is well vegetated and, unfortunately, evidence of the
original drill site has been obliterated. Even after an extensive search, the borehole
was not found. The earlier GSC dataset was obtained in 1976 and is shown on Figure
2. A change in climate in this area over the last two centuries should have caused a
temperature perturbation down to 100-200 m depth in this hole, but this is obviously
not recorded. The data are almost a perfect straight line.
Figure 2. Whitehorse hole. GSC refers to the Geological Survey of Canada.
Northern latitude ground-surface-air temperatures 7
3.2. Ruby Creek
The Ruby creek site is about 27 km northeast of Atlin, B.C. and, by the time of this
writing is an active Molybdenum mine. The area is in an area of significant topographic
relief at high alpine elevations. Vegetation is sparse and typical of alpine environments.
The two original Ruby creek boreholes were logged to depths of 305 and 350 m in a
granitic batholith. Unfortunately, the original hole collars were destroyed by exploration
activities. We managed to log another more recent hole (48), quite close (about 100 m)
to the original holes identified by the GSC (see Figure 3). The water table at depth at
this site is not known. Jessop et al. (1984) believed that the thermal gradients in the
upper portion of the holes were disturbed by groundwater flow. A comparison between
the synthetic T −z plot and the observed data indicates that the warming of the ground
surface and subsequent propagation downward according to a purely conductive heat
transfer model has not occurred. Yet, we know the SAT signal at the surface shows a
linear increase of about 1.45 C over 54 years.
3.3. Dease Lake
This hole was originally drilled with the aim of collecting heat flow data. The borehole
was found to be in excellent shape in a well forested creek area. The site is within a
few km of Dease Lake itself. Little vegetative changes have been noted in the area since
the 1960s. The water table is at the surface, and the hole was logged without incident.
Results are show on Figure 4. The older GSC data are shown as black dots. Only the
top 200 m of the hole is plotted, and the results show excellent correspondence between
the various data sets. The upward trending curve above 5 m is suggestive of the yearly
thermal cycles and not of climate change.
3.4. Hotailuh/ Gnat Lake
The original hole (Hotailuh) was found intact and in excellent condition. It was
completed to 427 m into a granitic batholith in an area that has seen its share of
exploration activities. It is just a few km from the Gnat Lake site. As mentioned by
Jessop et al. (1984) portions of this hole were considered to be disturbed by groundwater
flows in fractured horizons (150 m and 350 m) within the granite. The results of recent
surveys and that of the past are shown on Figure 5. The water table is at the surface,
and the hole was logged without incident. The older GSC data are shown as black
rectangles. Only the top 200 m portion of the hole is plotted, and the results show
excellent correspondence between the various data sets over the entire borehole length.
No change in surface temperature is evident at this site between 1972 and 2006, a
situation that is noticeably different with the SAT record at the site. The upward
trending curve above 5 m is suggestive of the yearly thermal cycles and not climate
change. We also show the data recorded by Jessop et al. (1984) in 1972 for Gnat Lake.
Unfortunately, only a few data points are available at depths less than 40 m. We were
Northern latitude ground-surface-air temperatures 8
Figure 3. Ruby Creek (Atlin) hole. Data recorded at site but not in the same
borehole. Dots recorded in the older hole.
not able to find the hole and of course, log more data.
3.5. Buckley Lake/ Stikine Site Z
This site was drilled near the shore of a small lake just north of the Mount Edziza
Volcanic complex, which is a continuous volcanic terrain the extends some 60 km south
of Buckley Lake. The site itself is a partially cleared area in a heavily forested zone.
The hole is deep, some 427 m into predominantly quartzose rock. Only the first 200 m
of the record is plotted (Figure 6) and very close correspondence is seen between the
earlier records and that of the most recent survey. The water table in the hole is at 4.7
m, and the two shallow measurements were made in the air filled portion of the hole.
Northern latitude ground-surface-air temperatures 9
Figure 4. Dease Lake
Again, none of this data suggests external climate forcing.
An additional site in the area was analyzed for long term temperature records, and
this is detailed in an earlier section, but no temperature logs are available. North of the
Edziza complex is the grand canyon of the Stikine River, which is a deep, narrow canyon
that cuts through bands of layered volcanic and sedimentary rocks. In the 1980’s B.C.
Hydro was actively engaged in groundwork for two very large dams in the Grand Canyon
of the Stikine. These projects were later abandoned due to environmental concerns.
Northern latitude ground-surface-air temperatures 10
Figure 5. Hotailuh and Gnat Lake holes
3.6. Ritchie
Measurements were originally obtained in a large diameter (121 mm) petroleum
exploration hole to a depth of 1890 m by Dome Petroleum. The site is on the side
of a steep mountain (elevation 1100 m), along a tributary of the Bell Irving River, some
20 km east of Bowser Lake. Data from this hole originates from 1970 to 1972, and was
not surveyed in 2006 so we do not have more recent data to compare (see Figure 7).
Jessop et al. (1984) note that the temperature data had to be corrected for both climatic
changes and topographic relief in order to correctly determine heat flows. However, a
climate related GST signal is not plausible at this site and the observed profile is likely
affected by the steep topography at the site. The odd anomaly above 40 m is much to
Northern latitude ground-surface-air temperatures 11
Figure 6. Buckley Lake hole
deep to be related to an annual cycle, but the water table depth in the hole at the time
of the survey is not known.
4. Discussion
A review of Figures 1-6 shows that the known climate signal determined from the SAT
record has not propagated an anomalous temperature signal to depth as predicted by
a conceptual model of 1-D diffusive heat transport. Conversely any attempts at using
inverse methods that are based upon heat diffusion would, no doubt, predict a flat GST
history from 1800 to present, if based solely on the boreholes presented in this work.
Clearly, over a large area in northern British Columbia some other mechanism must
Northern latitude ground-surface-air temperatures 12
Figure 7. Ritchie hole
be responsible for removing the energy that should have been imported to the ground
surface in response to the SAT increases. As mentioned in the introduction, there is
a complex interplay between SAT and GST. It has been noted that the magnitude of
temperature increases reconstructed from BHT records seems to contrast with some
proxy based reconstructions of SAT that indicate less amounts of warming over the
same period (Zhang, 2005; and references therein). There can be many reasons for this,
but the influence of seasonal snow cover cannot be underestimated as a contributing
factor for modifying the climate signals reconstructed from BHT records.
According to Zhang (2005), snowmelt dates in Northern Alaska have advanced by
around 8 days since the 1960’s. Some modeling suggests that an advance of 10 days of
snow melt should lead to an increase in GST by 0.2 oC. However, Zhang notices that
Northern latitude ground-surface-air temperatures 13
a decrease in snow depth leads to a decrease in soil temperatures because of a lack of
snow insulating cover. Brown and Braaten (1998) report a snow depth decrease in much
of Canada over the period of 1946-1995. But, there has been about a 12 cm increase in
snow depth between 1946-1995 for each month December and January (total increase
of about 24 cm for the two months combined) for portions of northwestern British
Columbia (but nowhere else) and no change in snow depth for any other months for any
of our region. There has been no change in snow cover duration in our area of interest
except for spring (MAM) that shows about a 2 week decrease in snow cover duration
between 1946-1995 (49 years) - this essentially suggests that the snow disappears two
weeks earlier in some places compared to the mid/late-1940’s. Upon further reflection,
Zhang (2005) states that “The effect of early snow cover with late snow melt and and
late snow cover with early snow melt would change the mean annual ground surface
temperature by +2.0o and -1.5 oC, respectively”
So therefore, we conclude that a trend in our area towards late snow accumulation
and early thaw are masking an the increase in SAT temperatures. The snow cover
leads to a disconnect between SAT and GST over the autumn and winter months. The
important summer months, at least from the perspective of signal coupling, shows shows
a flat SAT response. Overall then, no (effective) increase in average climate is imported
into the ground.
Lastly Mann and Schmidt (2003), through coupling of GCM’s and land surface
schemes allowing for snow cover, show that SATs in North America closely track GST
only during the warm season. During the cold season an insulation effect is dominant
and this is supported by Zhang (2005). In our observational area, we have a trend in
warmer temperatures in the winter and spring, but flat or cool over the summer. This
may then explain why the boreholes do not reflect the GST, and the SAT is disconnected.
These results are important in that they support Mann and Schmidt’s conjecture about
a seasonal bias in the GST reconstructions from borehole surveys.
5. Conclusions
In this paper, eight sites in north-western Canada, west of the Cordillera, are examined
for long-term SAT changes. At seven of these sites precise temperature profiles are
used for the first time since (in some cases) the 1960’s in order to explore the linkage
between GSTs and SATs. The borehole logs and their descriptions were taken from
the the Geologic Survey of Canada’s repository of temperature recordings. We link the
results of new readings at four sites taken in 2006 with those previously, and also to the
instrumental atmospheric records for observation and interpretation. The exciting part
of this analysis is that in all cases we looked at little land use changes have occurred for
over 25 years.
All eight sites show a statistically significant increasing trend, > 95% in most
cases, in annual mean minimum and maximum temperatures (Table 1). Over the 54
year period, the increase in minimum temperatures has been between 1.1o and 1.5o and
Northern latitude ground-surface-air temperatures 14
the increase in maximum temperatures has ranged between 0.8C and 1.5C over the
eight stations. All stations, except for White Horse, have larger increases in minimum
temperatures compared to maximum temperatures, which is consistent with Zhang et
al. (2000). Tables 2 - 5 suggest that the annual mean trends are significantly influenced
by winter (DJF) and spring (MAM) temperature trends as opposed to summer (JJA)
and autumn (SON). Mean annual winter minimum temperature trends range between 2o
and 4o over the 54 year period, while mean annual winter maximum temperature trends
range over 1.9o to 4.2o, all being statistically significant to > 90% confidence. Once
again, the minimum temperature trends tend to be slightly larger than the maximum
temperature trends at most stations. The spring temperature trends (Table 3) are much
smaller than the winter trends (Table 2), however, spring trends still remain all positive
with most of them statistically significant at the 90% level. Tables 4 and 5 indicate that
summer and autumn do not have any statistically significant temperature trends since
all confidence levels are less than 80%, with most of them much lower than this (not
indicated in the tables).
This research shows that the known climate signal determined from the SAT record
over a large portion of north-west British Columbia and the southern Yukon has not
propagated an anomalous temperature signal to depth as predicted by a conceptual
model of 1-D diffusive heat transport. Conversely any attempts at using inverse methods
that are based upon heat diffusion would, no doubt, predict a flat GST history from
1800 to present, if based solely on the boreholes presented in this work. Clearly, some
other mechanism must be responsible for removing the energy that should have been
imported to the ground surface in response to the SAT increases. Our hypothesis is
that the observed disconnect between the SAT and GST signals at eight of our sites is
caused by an increase in snow cover in early winter, followed by an increasing trend to
an earlier snow melt in the region. A trend in our area towards late snow accumulation
and early thaw are masking the increase in SAT temperatures. The snow cover leads
to a disconnect between SAT and GST over the autumn and winter months. The
important summer months, at least from the perspective of signal coupling, shows a flat
or statistically insignificant SAT response.
There are limitations in our study. We were not able to obtain recent BHTs at
four of the eight sites. We do not have precise snow depths, and other detailed weather
records from any of the sites. The temperature trends at each site are determined from
statistical analyses of the CANGRID dataset and finally, no detailed modeling efforts
were carried out at any of the sites. Obviously, more work needs to be done but we
do believe that they support Mann and Schmidt’s (2003) conjecture about a seasonal
bias in the GST reconstructions from borehole surveys and counters assertions of lower
historic earth temperatures west of the Cordillera in northern British Columbia.
Northern latitude ground-surface-air temperatures 15
Table 1. Annual trends analysis (from 1950 - 2003) results of minimum and
maximum temperature (t-min/t-max) at different stations.
Station name oC per 54
years period
Z-Stats. Confidence
level (%)
(min/max) (min/max) (min/max)
White Horse 1.49/1.49 2.42/2.60 99.1/98.4
Ruby Creek 1.45/1.42 2.32/2.50 98.7/97.9
Dease Lake 1.26/1.07 2.16/2.42 98.4/96.9
Grant Lake 1.22/1.02 2.25/2.36 98.1/97.5
Buckley Lake 1.14/0.92 2.35/2.31 97.9/98.1
Stikine Site Z 1.13/0.88 2.23/2.26 97.6/97.4
Ritchie 1.06/0.79 2.09/1.68 90.7/96.3
Table 2. Winter (Dec to Feb) trends analysis (from 1950 - 2003) results of
minimum and maximum temperature (t-min/t-max) at different stations.
Station name oC per 54
years period
Z-Stats. Confidence
level (%)
(min/max) (min/max) (min/max)
White Horse 4.03/4.24 1.78/2.02 92.5/95.7
Ruby Creek 3.86/3.73 1.84/2.02 93.4/95.7
Dease Lake 3.24/3.25 1.84/1.74 93.4/91.8
Grant Lake 3.06/2.92 1.87/1.81 93.9/92.9
Buckley Lake 2.84/2.59 1.79/1.98 92.7/95.2
Stikine Site Z 2.82/2.64 1.87/1.96 93.9/95.0
Ritchie 2.05/1.91 1.81/2.05 92.9/95.9
Table 3. Spring (Mar to May) trends analysis (from 1950 - 2003) results of
minimum and maximum temperature (t-min/t-max) at different stations.
Station name oC per 54
years period
Z-Stats. Confidence
level (%)
(min/max) (min/max) (min/max)
White Horse 1.73/2.16 2.14/2.05 96.8/95.9
Ruby Creek 1.68/1.88 2.01/1.92 95.4/94.5
Dease Lake 1.66/1.69 2.08/1.83 96.2/93.3
Grant Lake 1.65/1.67 2.08/1.72 96.2/91.5
Buckley Lake 1.55/1.29 2.23/1.86 97.4/93.7
Stikine Site Z 1.52/1.49 2.36/1.86 98.2/93.7
Ritchie 1.19/1.29 1.92/1.59 94.4/88.8
Northern latitude ground-surface-air temperatures 16
Table 4. Summer (Jun to Aug) trends analysis (from 1950 - 2003) results of
minimum and maximum temperature (t-min/t-max) at different stations.
Station name oC per 54
years period
Z-Stats. Confidence
level (%)
(min/max) (min/max) (min/max)
White Horse 0.68/0.51 1.23/0.77 -/78.1
Ruby Creek 0.56/0.42 1.01/0.63 -/68.3
Dease Lake 0.33/-0.17 0.63/-0.28 -/-
Grant Lake 0.28/-0.22 0.44/-0.45 -/-
Buckley Lake 0.35/-0.28 0.57/-0.51 -/-
Stikine Site Z 0.29/-0.30 0.47/-0.59 -/-
Ritchie 0.31/-0.17 0.81/-0.36 -/-
Table 5. Autumn (Sep to Nov) trends analysis (from 1950 - 2003) results of
minimum and maximum temperature (t-min/t-max) at different stations.
Station name oC per 54
years period
Z-Stats. Confidence
level (%)
(min/max) (min/max) (min/max)
White Horse 0.01/-0.22 0.00/-0.24 -/-
Ruby Creek 0.05/-0.14 0.01/-0.21 -/-
Dease Lake 0.00/-0.16 0.00/-0.25 -/-
Grant Lake 0.11/-0.04 0.10/-0.01 -/-
Buckley Lake 0.23/0.09 0.44/0.01 -/-
Stikine Site Z 0.23/0.01 0.33/0.00 -/-
Ritchie 0.46/0.38 0.93/0.82 -/-
[] Beltrami, H. (2001), On the relationship between ground temperature histories and meteorological
records: A report on the Pomquet station, Global and Planetary Change, 29(3-4), 327-348.
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Northern latitude ground-surface-air temperatures 17
1950 1956 1962 1968 1974 1980 1986 1992 1998 2003−3.5
−3
−2.5
−2
−1.5
−1
−0.5
0
0.5
1
1.5
White Horse
Time (Year)
Mea
n a
nnual
max
imum
tem
per
ature
(oC
) Equation of the line: Y = 0.030022X −1.6917
1950 1956 1962 1968 1974 1980 1986 1992 1998 20032.5
3
3.5
4
4.5
5
5.5
6
6.5
7
Ruby Creek
Time (Year)
Mea
n a
nn
ual
max
imu
m t
emp
erat
ure
(oC
) Equation of the line: Y = 0.027482X + 3.9192
1950 1956 1962 1968 1974 1980 1986 1992 1998 20033.5
4
4.5
5
5.5
6
6.5
7
7.5
8
Dease Lake
Time (Year)
Mea
n a
nn
ual
max
imu
m t
emp
erat
ure
(oC
)
Equation of the line: Y = 0.022003X + 4.8755
1950 1956 1962 1968 1974 1980 1986 1992 1998 20033
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
Grant Lake
Time (Year)
Mea
n a
nn
ual
max
imu
m t
emp
erat
ure
(oC
)
Equation of the line: Y = 0.021151X + 4.9241
1950 1956 1962 1968 1974 1980 1986 1992 1998 20031.5
2
2.5
3
3.5
4
4.5
5
5.5
6
Buckley Lake
Time (Year)
Mea
n a
nn
ual
max
imu
m t
emp
erat
ure
(oC
)
Equation of the line: Y = 0.019219X + 3.3215
1950 1956 1962 1968 1974 1980 1986 1992 1998 2003−0.5
0
0.5
1
1.5
2
2.5
3
3.5
Stikine Site Z
Time (Year)
Mea
n a
nnual
max
imum
tem
per
ature
(oC
)
Equation of the line: Y = 0.019108X + 1.0088
1950 1956 1962 1968 1974 1980 1986 1992 1998 20031
1.5
2
2.5
3
3.5
4
4.5
5
Ritchie
Time (Year)
Mea
n a
nn
ual
max
imu
m t
emp
erat
ure
(oC
)
Equation of the line: Y = 0.016375X + 2.9888
Figure 8. Mean annual maximum temperature (oC) trend for seven stations [White
Horse, Ruby Creek, Dease Lake, Grant Lake, Buckley Lake, Stikine Site Z, and Ritchie].
Northern latitude ground-surface-air temperatures 18
1950 1956 1962 1968 1974 1980 1986 1992 1998 2003−13
−12
−11
−10
−9
−8
−7
White Horse
Time (Year)
Mea
n a
nnual
min
imum
tem
per
ature
(oC
)Equation of the line: Y = 0.02933X −10.3092
1950 1956 1962 1968 1974 1980 1986 1992 1998 2003−8
−7.5
−7
−6.5
−6
−5.5
−5
−4.5
−4
−3.5
−3
Ruby Creek
Time (Year)
Mea
n a
nnual
min
imum
tem
per
ature
(oC
) Equation of the line: Y = 0.028211X −5.7704
1950 1956 1962 1968 1974 1980 1986 1992 1998 2003−8
−7.5
−7
−6.5
−6
−5.5
−5
−4.5
−4
−3.5
Dease Lake
Time (Year)
Mea
n a
nnual
min
imum
tem
per
ature
(oC
)
Equation of the line: Y = 0.025775X −6.4836
1950 1956 1962 1968 1974 1980 1986 1992 1998 2003−8
−7.5
−7
−6.5
−6
−5.5
−5
−4.5
−4
Grant Lake
Time (Year)
Mea
n a
nnual
min
imum
tem
per
ature
(oC
) Equation of the line: Y = 0.024583X −6.4066
1950 1956 1962 1968 1974 1980 1986 1992 1998 2003−7
−6.5
−6
−5.5
−5
−4.5
−4
−3.5
−3
Buckley Lake
Time (Year)
Mea
n a
nnual
min
imum
tem
per
ature
(oC
)
Equation of the line: Y = 0.023171X −5.3148
1950 1956 1962 1968 1974 1980 1986 1992 1998 2003−9.5
−9
−8.5
−8
−7.5
−7
−6.5
−6
−5.5
Stikine Site Z
Time (Year)
Mea
n a
nnual
min
imum
tem
per
ature
(oC
)
Equation of the line: Y = 0.023145X −7.8194
1950 1956 1962 1968 1974 1980 1986 1992 1998 2003−6.5
−6
−5.5
−5
−4.5
−4
−3.5
−3
−2.5
Ritchie
Time (Year)
Mea
n a
nnual
min
imum
tem
per
ature
(oC
)
Equation of the line: Y = 0.02013X −4.7182
Figure 9. Mean annual minimum temperature (oC) trend for seven stations [White
Horse, Ruby Creek, Dease Lake, Grant Lake, Buckley Lake, Stikine Site Z, and Ritchie].
Northern latitude ground-surface-air temperatures 19
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