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Isle Royale Climate Change Table

This page is part of the project: Isle Royale

Data Quality Statement:

There are no continuous time series data for Isle Royale.  Of the data that do exist for Isle Royale, they consist mostly of observations from the warm-season and few observations exist for the cold-season.  Of the observations that are directly measured, such as temperature, precipitation, and snowfall, snowfall records are especially lacking.  Since data at Isle Royale are not reliable it is necessary to use records from nearby regions that are of higher quality.  We recommend using reliable observational records from areas to the west and north (MN and Canada), as opposed to records from the mainland to the south (Michigan's Upper Peninsula), because the distance from shore is minimal and those stations, similar to Isle Royale, are not in the heavy lake-effect zones.  Minnesota's weather station at Grand Morais, MN[bib]927[/bib] is used for some of the historical trends in the table below.


link to the table


Table Summary:

Isle Royale's climate is defined by its maritime location in the western basin of Lake Superior, the largest of the Great Lakes.  The island is about 15 miles from the closest shorelines of Minnesota and Canada and located near Thunder Bay.  The wintertime weather and climate of the Great Lakes and the near-shore land are strongly influenced by whether or not the lakes freeze.   Some of the characteristic weather and climate patterns at Isle Royale have been changing as the planet warms.  The local effects of Lake Superior are not represented in climate models or gridded observational data sets used to assess changes in recent decades.  Therefore, it is necessary to tailor information from these standard data sources with the influences of local conditions.  

The factors influencing the local climate at Isle Royale often have positive feedbacks that accelerate changes.  This is especailly true for lake ice.  Warming air temperatures are correlated to warming surface lake waters, which translates to decreased lake ice cover during the cold season.  Lake Superior waters are warmer going into the cold season causing it to take longer for ice to form, and with spring temperatures warming, too, the ice is melting earlier.  The region of Lake Superior where Isle Royale resides historically has had some of the thickest ice formation but rarely forming a complete ice bridge to the island.  Though localized processes involved in the formation of an ice bridge between Isle Royale and the continent are difficult to evaluate, all of the current changes in environmental variables suggest that the ice bridge will occur less frequently.

Air temperatures at Isle Royale may warm less quickly than temperatures over the mainland (continental locations), because Lake Superior water temperatures act as an insulator keeping warm-season temperatures slightly cooler and cold-season temperatures slightly warmer.  In recent decades Lake Superior's surface temperatures have warmed more quickly than over land, suggesting a strong relation to lake circulation.  These circulation effects are related to mixing of shallow and deep lake water, and potentially have impacts on local weather and climate as well as lake ecosystems.

Warm-season precipitation at Isle Royale is slightly less than areas farther inland because Lake Superior creates a stable atmosphere over it's relatively cool surface waters.  Although annual precipitation has increased at Isle Royale, precipitation during the expanding warm-season (growing season) may actually be less in the future due to the influence of Lake Superior. Uncertainty in how cold-season precipitation will change is strongly influenced by how ice cover might change.  In general, Isle Royale experiences slightly more precipitation (wet or dry) during the cold-season than locations inland because it receives lake-effect precipitation from Lake Superior.  Warmer surface waters that prevent ice formation will allow greater moisture flux to the atmosphere and greater potential for increased precipitation.  The strong impact that this warming will have on precipitation on the downwind shore of the Great Lakes is not expected at Isle Royale.  The fetch between the mainland and the island is only a few miles.  Hence, the air does not have the opportunity to accumulate as much water.  In addition the land-area of the island is small so the island does not have the characteristics of a continental land mass.  Therefore, the large changes that are expected in the snow belt parts of the Great Lakes, do not obviously happen on Isle Royale; such effects would be greatly muted.   If air temperatures do not warm beyond the necessary conditions for producing snow, more precipitation will fall as snow, otherwise, increased rain events can be expected.  Given November is historically the month with the greatest extreme snow events, there may be more intense blizzards or transition to rain events during that time in the future.  

Year round warming in the northern latitudes also has had effects on how weather patterns move across the region. This is consistent with theory and observations.  Climate projections don't model the processes associated with these changes very well.   Weather systems are moving more slowly leading to persistent periods of weather that provide greater potential for drought, flood, cold and warm-spells.                                    



Important Definitions for the Table:

Arctic Oscillation (AO) - The Arctic Oscillation is a pattern in which atmospheric pressure at polar and middle latitudes fluctuates between negative and positive phases. The negative phase brings higher-than-normal pressure over the polar region and lower-than-normal pressure at about 45 degrees north latitude. The negative phase allows cold air to plunge into the Midwestern United States and western Europe, and storms bring rain to the Mediterranean. The positive phase brings the opposite conditions, steering ocean storms farther north and bringing wetter weather to Alaska, Scotland and Scandinavia and drier conditions to areas such as California, Spain and the Middle East. The North Atlantic Oscillation is often considered to be a regional manifestation of the AO. (source:

North Atlantic Oscillation- The NAO is a large-scale fluctuation in atmospheric pressure between the subtropical high pressure system located near the Azores in the Atlantic Ocean and the sub-polar low pressure system near Iceland and is quantified in the NAO Index. The surface pressure drives surface winds and wintertime storms from west to east across the North Atlantic affecting climate from New England to western Europe as far eastward as central Siberia and eastern Mediterranean and southward to West Africa (source:

Here is another link for the AO and NAO:

ENSO (El Niño-Southern Oscillation) - Originally, ENSO referred to El Niño/ Southern Oscillation, or the combined atmosphere/ocean system during an El Niño warm event. The ENSO cycle includes La Niña and El Niño phases as well as neutral phases, or ENSO cycle, of the coupled atmosphere/ocean system though sometimes it is still used as originally defined. The Southern Oscillation is quantified by the Southern Oscillation Index (SOI).(source


Note about references/bibliography:  References that are cited more than once only appear once in the numbered list of references but each instance is marked alphabetically ("a,b,c...").  In the text you may click on the superscript reference number to be taken to its bibliographical information, or, in the bibliography you may click the number or alphabetical listing to be taken to where the reference exists in the text.  Clicking the title of the reference will take you to its dedicated page with additional information (including how to access the resource).


Reference List
NCDC State Climatologies
Impacts of the Great Lakes on regional climate conditions
Evaluation of Potential Impacts on Great Lakes Water Resources Based on Climate Scenarios of Two GCMs 
Chapter 6: Great Lakes Ice Cover
Can CGCMs simulate the twentieth-century "warming hole" in the central United States? 
Effects of using air temperature as a proxy for potential evapotranspiration in climate change scenarios of Great Lakes basin hydrology 
Will There Be a Significant Change to El Nino in the Twenty-First Century? 
Confronting Climate Change in the Great Lakes Region
Temporal and Spatial Variability of Great Lakes Ice Cover, 1973-2010 
Trends in Twentieth-Century U.S. Extreme Snowfall Seasons
A new look at lake-effect snowfall trends in the Laurentian Great Lakes using a temporally homogeneous data set 
Adapting to Climate Change: A Planning Guide for State Coastal Managers