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Climate Drivers Table

This page is part of the project: Apostle Islands

Climate Parameter Trend Historical Change Localization Projected mid-21st Change Projected late-21st Change Confidence



The last 22 years (1991-2012) have been on average 2 degrees (F) warmer than the 1901-1960 average. (source: NCA data from Figure 2.7

Regionally, the greatest warming has occurred during winter (2.9 deg. F) and spring (1.6 deg. F) over the last 50 years. (source: GLISA Northwestern WI Climate Division Climatology)  Since 1950, Madeline Island has warmed the most during spring (2.3 deg. F) and summer (2.4 deg. F).(source: GLISA analysis for Madeline Island Station Data)

Temperatures throughout the year at Madeline Island are slightly less variable than nearby inland locations. (source: U Wis. Station Data)

Midwest Temperature Projections:

winter: +4 to 7 deg(F) change

spring: +2 to 7 deg(F) change

summer: +2 to 8 deg(F) change

fall: +3 to 6 deg(F) change

(source: NOAA Technical Report Figure 32)

+1 to 6 degrees (F) increase in annual average temperature1

+3.5 to 112 degrees (F) increase in annual average temperature (source: NCA data from Figure 2.9)  All seasons are projected to warm but winter is expected to experience the most warming. (source: NCA Technical Input Report) There is a clear historic warming trend and models agree with future average warming.  The amount of warming is less certain, especially at the local scale.
Extreme Temperature Events no change to +

Days with maximum temperatures over 90 deg (F) have increased from 16 days during the 30-year period of 1950-80 to 73 days during the 30-year period of 1981-2010 at Madeline Island. Days with temperatures below 10 deg (F) have stayed roughly the same for the two consecutive periods (217, 207).  (source: U Wis. Station Data)

Regionally, the average number of days each year below freezing from 1980-2000 was 150-170.(source: NCA Technical Input Report)

Compared to weather stations farther inland (Gordon and Solon Springs), Madeline Island experiences fewer hot days (above 90 deg F) and fewer days below 10 deg (F).    The northern Midwest is projected to have no change to slight increases (0-5 more days per year) in days above 95 deg (F). (source: NCA Figure 18.2) The maximum number of consecutive hot days is also projected to stay the same or increase by less than 5 additional days per year. (source: NCA Technical Input Report) Northern WI is projected to have 2-3 weeks fewer of temperatures below freezing.(source: NCA Technical Input Report)   For the Midwest region there is higher confidence that cold days will warm more than hot days.  However, the trend for Madeline Island has been more hot days and the same number of cold days.  
Precipitation + & -

Annual average precipitation in the last two decades (1991-2012) has been about 4% higher than the 1901-1960 average. (source: NCA data from Figure 2.12)

Regionally, fall precipitation has increased the most (21%) over the last 50 years.  Spring and Summer precipitation have shown declines (-1.4% and -7.1%, respectively). (source: GLISA Northwestern WI Climate Division Climatology) Since 1950, Madeline Island has experienced a similar trend of decreasing spring and summer precipitation (-6.8% and -25.7%, respectively) and increases to fall and winter precipitation (18.6% and 16.4%, respectively). (source: GLISA analysis for Madeline Island Station Data)

Madeline Island experiences more uniform precipitation amounts throughout the year compared to locations farther inland. (source: U Wis. Station Data)

Climate models project a wide range of future precipitation trends.  Here, seasonal ranges (measured in percent change) are reported for the Midwest, and model averages (measured in inches) are reported in parenthesis for Northern WI.  

winter: -5 to +15% change (1")

spring: -5 to +15% change (1")

summer: -20 to +20% change (0") Zero mean change is representative of future trends being negative or positive.

fall: -10 to +20% change (0.5")

annual: -7 to +12% change (2.5")

(Midwest ranges source: NOAA Technical Report Figure 43; Northern WI averages source: WICCI Maps p22-25)

On average, winter and spring precipitation is projected to increase by 10-30%.3    Summer and Fall precipitation have high uncertainty and could have large increases or decreases. (source: NCA data from Figure 2.14/2.15) In general, there is stronger evidence for increases during winter and spring and high uncertainty for future summer/fall precipitation.  The strong positive trend during Fall for NW Wisconsin suggests a possible increase in the future.

- (regionally)

+ (locally)

Northwest WI has on average 55" +/- roughly 20" of snowfall each year. During the 1950-2010 period, the earlier years were characterized by less snowfall and later years characterized by more snowfall on average.  (source: U. Wisconsin climate division data)

Roughly 25% of winter precipitation on the Bayfield Peninsula is from lake-effects.4

Apostle Islands is on the edge of the lake-effect snow zone, which has had increasing snowfall amounts over the last few decades while most of the Midwest has had decreases.(source: GLISA Great Lakes Snow Summary) In the near term, lake-effect snow near Lake Superior may increase slightly, but most lake-effect precipitation will transition to rain as air temperatures rise.  The Bayfield Peninsula region may experience up to a few additional heavy lake-effect snowfall days per year.5 The increasing trend of lake-effect snowfall may reverse as fewer cold air outbreaks from Canada occur and air temperatures warm above freezing. Projections indicate 10-20 fewer days per year with daily snowfall of at least 1cm.  Winter precipitation is projected to increase up to 30% but it will not necessarily come in the form of snow.  Mean annual snowfall is projected to decrease by 20 to 40+ inches per year.6 Confidence in snow projections is low.
Extreme Precip Events + The Midwest has seen large increases in extreme precipitation events. (source: NCA Figure 2.17 Madeline Island has not seen a large change in the number or intensity of daily precipitation events exceeding 2 inches.  Two weather stations farther inland7 have seen larger increases in daily precipitation events.  8

No statistically significant change in the number of consecutive dry days in a given year.

Most models project large increases in heavy precipitation events (+23% increase in #days >1")

(source: NOAA Technical Report Figure 45 and table 8)

Extreme events are projected to occur more frequently (up to an average of 4 times more often under high scenario RCP 8.5). (source: NCA Figure 2.19)

10% increase in maximum annual number of consecutive dry days (source: NCA Figure 2.13)

In general extreme events are projected to increase, but regional differences will emerge.  There is medium confidence for increasing extreme events at Apostle Islands since there isn't a strong positive historic trend.

Frost-free Season + The growing season increased by about 2 weeks across the Midwest since 1950 mainly due to earlier last spring freezes. (source: NCA)  The average length of the frost free season from 1980-2000 was about 120 days (source: Technical Input to NCA)

Since 1950, Madeline Island has experienced an increase of 16 growing season days.9 The day of first (last) freeze on the island has occurred about 6 (11) days later (earlier) on average.(source: GLISA analysis for Madeline Island Station Data)  

Most of WI (including Apostle Islands) is projected to experience a frost-free season that is one month longer than present. (source: GLISA's maps of NCA data)   There is high confidence that there will be more days above freezing, but it is less certain that those days will occur consecutively.
Wind likely + Lake Superior has seen a 5% increase per decade in surface wind speeds measured by buoys from 1985-2008.10

Apostle Island is subject to experiencing lake and land breezes during the warm season.  

Extreme wind events in November have historically caused strong wind storms that impact shipping on Lake Superior as well as ice formation in general.  Strong winds can break up ice or prevent ice from forming.

  Wind events more extreme than the historical envelope will likely not develop until the end of the century. (source: Technical Input to NCA) There is low confidence in wind information because historical observations are lacking and future model simulations are poor.
Lake Levels No Change11

Lake Superior historic high: 603.4 ft above sea level (2 feet above present)

Lake Superior historic low: 599.5 ft above sea level (-2.5 feet below present) (source: NOAA Lake Level Viewer)

Intra-annual variability is about 1-2 feet (Great Lakes Water Level Dashboard)

Lows occur in spring (Mar/Apr)

Highs occur in late summer/early fall (Aug-Oct)

Lake Superior water levels show strong evidence for non-random trends.12 Levels increased from 1860-1980, then experienced a 30cm decrease from 1980-2007.  Since May of 2014 monthly mean water levels have been above the long-term (1918-2015) record.  There is an earlier shift to the spring maximum13 and slight decrease in net basin supply.14

Lake Levels primarily depend on the balance between over-lake precipitation, over-lake evaporation, and the horizontal (landscape) flow of water into/out of the lake. Lake Superior lake levels show a slight delay (about a month) in response to changes in the difference between precipitation and evaporation.  As there are net gains (precipitation > evaporation) lake levels increase and vice versa. 



Compared to the other Great Lakes, Lake Superior shows the least amount of future variability for changing lake levels.15
75% of models project no change to up to -0.5 meter lake level declines.  25% of models project up to 0.25 meter increases.15 The range of variability is only slightly expanded from mid-century projections with 75% of models still projecting no change or a slight drop in lake levels (up to about -0.6 meters).15  There is medium confidence in lake level projections for Lake Superior due to the complexity of the system that is being modeled and the range of variability that the models project (both increases and decreases).  
Lake Temperatures +

Lake Superior summer water temperatures have risen approximately 6 deg (F) over the last 100 years with most of the warming occurring during the last three decades.16

Water temperatures have varied up to 18 deg (F) during summer from year-to-year and by up to 10 deg (F) over multiple winters.(source: Great Lakes Statistics)

Warming temperatures, especially during Fall, cause a delay in ice formation.  Earlier warm spring temperatures initiate earlier ice melt. Water temperatures are projected to increase by as much as 7 deg (F) by 2050 (source: NCA) Water temperatures are projected to increase by as much as 12 deg (F). (source: NCA) The length of summer stratification17 is projected to increase up to 90 days for Lake Superior18 There is much evidence to suggest future warming water temperatures, however, the rate of warming may not continue to increase faster than the air temperature.
Lake Ice Cover - Lake Superior ice cover decreased 79% between 1973-201019 Lake Superior ice forms first in the western basin along the shallow southern shoreline.20 Apostle Islands is also one of the last regions in the western basin to maintain ice. (see satellite image from 3/28/15) Ice cover reaches a maximum during late winter/early spring and is diminished by warm surface water temperatures and winds (wave action) at the surface. Average ice duration for Lake Superior's western basin is projected to decrease to 10-13 weeks from the historic (1951-1995) average of 16 weeks.21 Average ice duration for Lake Superior's western basin is projected to decrease to 5-10 weeks from the average of 16 weeks (1951-1995).  Models project a wide range of variability for future ice-free winters in the western basin (7-43% of years ice free).22 There is high confidence that ice cover will decline in the future based on strong historical trends and indications of continued decreasing trends.  There is less evidence for a consistently ice-free Lake Superior in the next decade.
Arctic Oscillation Wildcard

It is difficult to predict the mode of the AO and one extreme negative mode can be followed by an extreme positive mode.  The modes determine the type of weather that is experienced: warmer and drier air (+) versus cooler and wetter air (-).  The AO is primarily a wintertime variable (DJFM).  The Great Lakes tend to have lower (higher) ice cover during the positive (negative) NAO.23

The negative phase of the AO is more strongly correlated with positive snowfall anomalies over North America than correlations of negative anomalies with a positive AO mode.  In general, the AO is more strongly correlated with snowfall over Eurasia than North America.24  

      There is low confidence in model projections of the AO. 
Weather "Blocking" Patterns Wildcard Observations do not indicate a significant increase in blocking occurrences in recent decades.  When Arctic air temperatures are warmer than temperatures to the south (i.e., as is the case for Arctic amplification), conditions are set up that increase high-latitude blocking and cause a southward shift in storm tracks, which occur as the AO shifts from positive to negative phase.  Since Arctic amplification has only recently distinguished itself from the natural variability of the climate system, there aren't enough observations to draw connections to events such as blocking.25       There is low confidence in information about future blocking patterns due to insufficiently long historical records for determining past trends, and poor model simulations of blocking in the northern hemisphere.26
ENSO Wildcard

"El Niño events are often associated with lower ice cover. The influence of La Niña on Great Lakes ice cover is intensity-dependent: strong (weak ) La Niña events are often associated with lower (higher) ice cover. The interference of impacts of ENSO and NAO complicates the relationship between ice cover and either of them."27

El Niño (La Nina) events are associated with diminished (increased) snowfall across the Great Lakes region compared to neutral ENSO seasons. (source:ENSO Impacts on United States Winter Precipitation and Temperature)

      There is low confidence in ENSO projections because ENSO and changes to ENSO are difficult to represent in climate models.28