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The impact of climate change and lake ice out dates in the Eastern United States
By
Frank Schneider1
The Pennsylvania State University
and
Richard H. Grumm
National Weather Service in State College
Abstract:
An examination was made of lake ice out data over the eastern United States. Ice out data was
obtained from Minnesota to Maine. Every lake examined showed a general trend toward earlier
ice out dates. In addition to ice out dates, a few lakes had both ice-in and ice-out data allowing
the examination of the changes in total ice days. Similar to ice out dates, the length of time
lakes are iced over shows a trend toward a later total time of ice cover. The few lakes examined
showed a trend toward a later beginning of the ice season.
National Weather Service Cooperative Observing site data in close proximity to several of the
lakes were examined. These data showed a basic trend toward warmer late winter and early
season mean temperatures similar to the trend in earlier ice out dates. In general warm March
and April weather was associated with the earlier ice out dates. Conversely cold late winter and
early springs were associated with the later ice out dates, which often extended into late April
and May during the coldest years.
1
Lead author and primary researcher as part of an undergraduate internship at the National Weather Service in
State College Autumn semester 2012.
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1. Introduction
Climate change is normally approached from the perspective of changes in the
temperatures regional domains, often using single observing locations, or large geographic
regions of the globe. The issue is often presented related to warmer winters, warmer
summers, changes in precipitation patterns, and tropical storm intensities. The local effects
of climate change such as the changes in the growing season length and changes in the
foliage are more local and tangible to people. This study uses lake ice out data in an
attempt to bring the concept of climate change to a more local level with potential impacts
that are tangible to the general public.
This paper examines lake ice data and its potential relationship with climate change.
Lake ice out data is far more readily available than lake ice in dates. Thus, it is easier to
examine the change in ice out dates relative to ice in and the total length of time a lake may
be covered by ice. Thus, this study focuses on the change of ice out dates over time which
can then be related back to climate change. This study of lake ice data was conducted to
assess climate change through the observations on the changes of ice out dates. This
approach brings the concept of climate change down to a very local and understandable
level.
The lake ice-out data were compared to nearby temperature data. Nearby, National
Weather Service (NWS) Cooperative Observing Program (COOP) sites were used to see if
there were any noticeable relationship between temperature and ice out dates. The 8 lakes
used in this study spanned from New England to Minnesota (Figure 1)
Lake
Ice-in Data
Ice-Out Data
Missing Data
Periods
Sunapee
n/a
1869-2012
none
Winnipesaukee,NH
n/a
1887-2012
none
Spofford, NH
n/a
1927-2012
none
Minnetonka, MN
n/a
1855-2010
1861-1876 and 1879-1886
Brant, NY
1908-2011
1908-2011
1910 and 1911
Medota, WI
1908 -2012
1908 -2012
1854 and 1855
Moosehead, ME
n/a
1848-2008
none
Ponkapoag, MA
n/a
1886-2008
none
Table 1. A listing of the lakes used in this study, the length of the record for ice in and ice out dates
when available. Missing data are noted as these data are often tracked by historical societies,
volunteers or other volunteer organizations.
2. Methods and Data
These data were obtained from a number of websites which tracked lake iceout dates. The Lake Sunapee data was obtained from the Sunapee Tower Office. The Lake
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Winnipesaukee data was gathered from Wikipedia. The Lake Spofford data was retrieved
from the Chesterfield, NH historical society. Lake Minnetonka’s data in Minnesota was
obtained from the Freshwater Society. Lake Brant’s data was retrieved from The Brant Lake
Association. Data on Moosehead Lake was obtained from the New England Water Science
Center in Maine. The observers were Kennebec Water Power Company and Maine
Department of Inland Fisheries and Wildlife. Data on Lake Ponkapoag was also obtained
from New England Water Science Center in Maine, and the observer was Blue Hills
Observatory.The National Weather Service (NWS) Cooperative Observing Program
(COOP) data were used to compare the ice out data to monthly mean temperature data.
These COOP data were obtained from the NWS XMACIS program or xm Applied Climate
Information System. The goal was to determine the relationships between changes in lake
ice to temperatures.
All the obtained data was analyzed and plotted in MS_Excel. The lake ice-out and if
available ice-in dates were in the format of year, month and day. These dates were
converted to the Julian date before an analysis was conducted to avoid issues related to
leap year. Thus all calculations are based on the day of the year not the calendar date. The
mean ice-out dates for each lake were computed and plotted to examine trends in ice-out
dates. Excel’s built in functions were used to produce regression analysis and trend lines.
All graphics using ice out data were produced using MS-Excel. A full suite of Excel
statistical analysis features were used to examine the mean, standard deviation, skewness
and Kurtosis of the ice out data.
3. Results
All the analyzed lakes showed a similar trend of earlier Ice out dates. There were
some lakes with more significant changes than others.
Two Lakes Brant in New York and Mendota in Wisconsin had both ice-in dates and
ice-out dates, allowing an analysis of the total days they were frozen over. As previously
stated, both lakes showed trends of decreasing total number of frozen-over. From 1908 to
2012, Lake Mendota had a decrease in the number of frozen-over days of about 19 days.
Earlier in the twentieth century the lake was frozen over for 106 days which has decreased
to around 87 frozen-over days (Figure 2). Over the same period, Lake Brant had a decrease
of about 6 days from 89 to about 83 days (Figure 3). It’s unclear as to why there was a
relatively smaller change in frozen-over days at Lake Brant relative to Lake Mendota. The
more northern latitude and interior continental location could play a role in the larger
changes at Lake Mendota relative to Lake Brant. Perhaps climate change and warming is
occurring more rapidly in central North America relative to the coastal regions.
The data from COOP sites that were within 15 miles of the lakes show that Mendota
(Figure4) had an average increase in temperatures for the month of March of around 8
degrees, while Lake Brant (Figure 5) shows an average temperature increase of about 2
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degrees with data reaching a decade past that of Mendota. These results suggest that
warming during the month of March is occurring faster in Wisconsin than New York.
The temperature scatter plot shows more variability of the yearly mean monthly
temperatures in Wisconsin relative to central New York (Figs. 4 & 5). The lake frozen-over
data supported these temperature data and show a similar trend. Lake Mendota had a
higher standard deviation and a much steeper regression line suggesting highly variable
data.
All data showed a negative trend, with an average of earlier ice out dates since the
data collection began. Three lakes, Moosehead (Figure 6), Mendota (Figure 7) and
Sunapee (Figure 8) had the longest and most consistent data records when compared with
the other lakes that were analyzed.
The trend analysis could be used to estimate how early the ice out dates will be in 10
or 60 years, assuming a steady increase in monthly temperatures. For example Moosehead
Lake (Figure 6) in Maine has expected ice out dates for 2020, 2040, 2070, of 122, 121, 119
days respectively, the ice season in the spring could be about 3 days shorter by 2070. The
data has some extreme variability in it and is reflected in the R^2 value, showing that the
trend line may not be a good predictor for ice out dates at any specific year. The trends
provide the only useful information over a period of time.
The data from all lakes suggested that 1945 was an interesting year with a
consistently earlier ice-out date at each respective lake. At 2 lakes 1945 had the earliest ice
out date at Sunapee and Moosehead lakes. The COOP data showed very high monthly
average temperature values for the March 1945 (COOP Data). This year there was actually
an instense heat wave in north america caused by a strong ridge that built over the middle
part of the country. (Figure 9) (Grumm 2011)
If you look at the ice out charts (ice out charts), you can see that the ice outs for the
lakes are occurring, on average, earlier each year. These trends are consistent with all the
lakes we have looked at so far.
We could use this data and trend lines to assess what the ice out dates might be in
the future, but as stated earlier with the example using Moosehead, the r^2 values are
relatively low. Meaning our trend lines don’t fit the data well, and give a fairly inaccurate
prediction.
The following tables show a statistical summary of the Lakes that were analyzed.
The r values are all relatively low, suggesting a weak correlation. Also from the table you
can see that all the data is skewed to the left, towards earlier ice out dates. It should be
noted that Brant,NY had some years were there was no ice over, so use with caution.
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Lake
R²
Regression Equation
Trend
Sunapee,NH
0.1538
y = -0.0961x + 299.99
Earlier Ice out
Winnipesaukee,NH
0.0868
y = -0.0799x + 264.53
Earlier Ice out
Spofford, NH
0.0745
y = -0.1296x + 357.52
Earlier Ice out
Minnetonka, MN
0.0203
y = -0.0339x + 169.57
Earlier Ice out
Brant, NY
0.0024
y = -0.0165x + 135.7
Earlier Ice out
Medota, WI
0.0864
y = -0.1705x + 107.4
Earlier Ice out
Moosehead, ME
0.1249
y = -0.0591x + 241.71
Earlier Ice out
Ponkapoag, MA
0.1763
y = -0.1696x + 406.01
Earlier Ice out
Table 2: Lake ice out data analysis showing the lake name and state, the r value, the regression equation and the
general trend of these data.
4. COOP Data
With an early look at the coop sites near some of the lakes. These data show a
correlation between rising temperatures and earlier Ice out dates. This trend was well
defined for Lake Mendota, Lake Sunapee and Moosehead Lake (Figure 10) (Figure 11)
(Figure 12).
It should be noted that the COOP data for Moosehead Lake (Figure 12) had a
significant amount of data missing. There was no data for 1933 and from 1949 to 1961.
Despite the missing data, the trend lines showed an unmistakable warming trend.
Lake
Julian Date
Average
Day of Year
Standard
Deviation
Skewness
Kurtosis
Sunapee,NH
113.47
23-Apr
10.19
-0.37
0.09
Winnipesaukee,NH
109.41
19-Apr
9.44
-0.39
0.33
Spofford, NH
101.41
11-Apr
10.43
-0.19
-0.10
Minnetonka, MN
103.56
13-Apr
9.54
-0.27
0.75
Brant, NY
103.36
13-Apr
8.03
-0.01
-0.44
Medota, WI
93.80
3-Apr
11.86
-0.23
0.04
Moosehead, ME
127.81
3-May
7.77
-0.18
0.22
Ponkapoag, MA
75.88
17-Mar
14.34
-0.71
0.07
Table 3: Statistical summary of all lakes. Data include the Lake name and State, the average ice-out date, the
corresponding day of the year, the standard deviation in days, the skewness and kurtosis of these data.
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5. Conclusion
The lake ice-out data provides evidence of local climate change over the past 100
years. Warmer springs are reducing the length of the ice season. For two lakes which had
both ice-in and ice-out data, a similar trend was observed in the autumn with later ice-in
dates and thus a slow reduction in the total number of days with ice cover. The impacts of
shorter ice seasons could lead to warmer lakes which could lead to changes to the flora and
fauna of these lakes, an area of worthy further study.
These data are in agreement with the IPCC studies related to CO2 emissions, at
least locally in the central and eastern United States, the climate has been warming. If the
role of CO2 is the cause of this warming, the ice out dates at all the lakes presented in this
study will continue to shift to an earlier date. Other studies have shown that the impact of
warming is stronger at higher latitudes. Recent changes in the Arctic Sea ice show similar, if
not more dramatic trends with rapidly decreasing ice in the Arctic during the spring and
summer and longer period of time to re-establish ice cover in the arctic. Both sea ice and
lake ice data show that at least in eastern United States and in the Arctic, climate change is
real and trending toward warmer conditions less conducive to maintaining ice on the lakes
of the eastern United States as long as it was in the first half of the 20th century.
The ice-out dates are trending towards earlier ice-out as the regional climate warms.
These data seem to imply a stronger effect in the upper Midwest relative to New England.
The COOP data support the ice-out data showing that the current warming trend is
occurring in both the upper Midwest and the northeast, with a sharper increase in the
Upper-Midwest. The focus here was on ice-out data during the spring months. However, the
yearly temperature trends are similar showing a gradual warming trend over the course of a
year. This implies that there will be less snowfall and more wintertime precipitation in the
form of rain. There is clearly a trend toward shorter and less severe winter seasons which
will decrease winter activities such as ice fishing, ice skating on lakes, and snowmobiling. A
recent article (NY Times 2012) suggested that climate change is decreasing the snow
season and will lead to a demise of many ski resorts in the eastern and southern United
States.
Conversely, warm season activities, such as cycling, swimming, fishing, and hiking
will increase with the lengthening warm season. A similar trend is already lengthening the
growing season. One issue with a lengthening growing season is the impact of late freezes
such as the freeze which followed the record warm conditions of March 2012 (Grumm
2012). Investments in warm season recreation will likely provide less risk than investments
in winter related activities. Pools, which traditionally are open from Memorial Day to Labor
Day, may have to rethink the length of the swimming season as the climate warms.
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In the autumn, the growing season will be longer, and foliage will occur at a later
date and will continue to do so as this trend persists. This could impact the leaf-tourist
industry in many parts of the United States and Canada. The data show a lot of variability
and therefore we cannot predict in detail the changes ahead, but the trends are clear and
we can tell that the Earth is warming and climate change is occurring.
6. Acknowledgements.
Thank you to the Pennsylvania State University for their wealth of COOP data that supports
my observations. Thank you to Rich Grumm for guiding me and aiding me with this project.
Most ice out data was retrieved via webpages. The Spofford Lake data was retrieved from
the Cheshire County, NH historical society in August 2012.
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Figure 1: A map of the all the locations of the lakes used in this study. A total of 8 lakes were used. (Return to text)
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Mendota, Days Frozen Over
y = -0.1705x + 432.47
R² = 0.0864
140
120
100
Ice over
80
days
60
Series1
Linear (Series1)
40
20
1900
1920
1940
1960
1980
2000
Year
Figure2: Scatter plot of the number of days Lake Mendota was frozen over. (Return to text)
140
Brant, Days Frozen Over
y = -0.0162x + 118.94
R² = 0.0005
120
100
Days Frozen 80
Over
60
Series1
Linear (Series1)
40
20
0
1900
1920
1940
1960
1980
Year
Figure 3: Number of Days that Lake Brant was frozen over (1908 to 1994) (Return to text)
2000
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Average Temperatures in March, Mendota
50
y = 0.1091x - 183.14
R² = 0.1772
45
40
35
Series1
30
Linear (Series1)
25
20
15
1940
1950
1960
1970
1980
1990
2000
2010
2020
Figure 4: Average temperatures in March for Lake Mendota. (Return to text)
Average Temperature for March, Brant
45
y = 0.0029x + 27.373
R² = 0.0002
40
Temperature
35
30
Series1
25
Linear (Series1)
20
1940
1950
1960
1970
1980
1990
2000
2010
2020
Year
Figure 5: Average temperature for Lake Brant in the month of march, ranging from 1943 to 2011. (Return to text)
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160
Moosehead Ice-Out Day
y = -0.0591x + 241.71
R² = 0.1249
140
Julian Day
Julian Day
120
Linear (Julian Day)
100
1850
1870
1890
1910
1930
Year
1950
1970
1990
2010
Figure 6: Julian Day that Lake Moosehead iced-out (1850 to 2008) (Return to text)
135
Mendota Ice-Out Days
125
y = -0.0973x + 281.92
R² = 0.1362
115
105
Julain Day 95
Series1
Linear (Series1)
85
75
65
55
1850
1900
1950
Year
Figure 7: Ice- out dates for Lake Mendota (Return to text)
2000
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Sunapee Ice-Out Day
y = -0.0961x + 299.99
R² = 0.1538
140
130
120
JulianDay
Linear (JulianDay)
Julian Days 110
100
90
80
1860
1880
1900
1920
1940
1960
Year
Figure 8: Julian Day that Lake Sunapee iced-out. (1869 to 2012) (Return to text)
1980
2000
2020
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Figure 9: As in Figure 1 except for the composite pattern and standardized anomalies from the 20th Century re-analysis data for the period of
0000 UTC 1 March through 1800 UTC 31 March 1945. (Return to text)
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Average Monthly Temperatures, Mendota
60
y = 0.0108x + 45.211
R² = 0.019
50
Temperature (F)
40
y = 0.0382x + 29.273
R² = 0.0951
30
20
February
March
10
y = 0.0292x + 18.881
R² = 0.0444
April
Linear (February)
1869
1875
1881
1887
1893
1899
1905
1911
1917
1923
1929
1935
1941
1947
1953
1959
1965
1971
1977
1983
1989
1995
2001
2007
0
Year
Linear (March)
Linear (April)
Figure 10: The average monthly air temperatures for the months of February, March and April for Lake Mendota (Return to text.)
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Average Monthly Temperatures, Moosehead
45
40
y = 0.0399x + 34.579
R² = 0.077
Temperature (F)
35
30
y = 0.0301x + 21.817
R² = 0.0223
25
20
15
February
10
March
5
y = 0.0724x + 9.4616
R² = 0.0931
1932
1936
1939
1942
1945
1948
1964
1967
1970
1973
1976
1979
1982
1985
1988
1991
1994
1997
2000
2003
2006
2009
2012
0
Year
April
Linear (February)
Linear (March)
Linear (April)
Figure 12: Average monthly air temperatures for February, March, and April for Lake Moosehead (Return to text)
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Average Monthly Temperatures, Sunapee
Temperature (F)
70
60
y = 0.0933x + 51.186
R² = 0.151
50
y = 0.0642x + 39.04
R² = 0.0787
40
February
30
y = 0.0591x + 29.962
R² = 0.0493
20
March
April
Linear (February)
10
Linear (March)
Year
Linear (April)
Figure 11: Average monthly air temperatures for the moths of February, March and April for Lake Sunapee (Return to text)