Great Lakes Regional Climate Change Maps

GLISA has created the following maps of observed and projected climate changes from analyses provided by the Cooperative Institute for Climate and Satellites to the Third National Climate Assessment.1 The maps are based on an ensemble of 1/8-degree statistically downscaled daily climate projections.2 No individual model is perfect. Each has strengths and weaknesses. We present the following maps as an overall regional consensus of temperature and precipitation projections, but models vary tremendously when comparing specific locations or different seasons within the region. To improve the precision and accuracy of future projections, GLISA is actively developing a Great Lakes Ensemble to identify models that best represent climate conditions in our region.

Average Annual Temperature

Projected increases in annual average temperature by 2041-2070 as compared to the 1971-2000 period, assuming emissions of greenhouse gases continue to rise (A2 scenario). Northern areas will likely see greater warming by mid-century. The Eastern Upper  Peninsula and Northern Lower Peninsula of Michigan may see particularly significant changes.

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Number of Days per Year Over 90°F

Projected change in number of days per year that exceed 90°F by 2041-2070 as compared to the 1971-2000 period, assuming emissions of greenhouse gases continue to rise (A2 scenario). While temperatures are rising faster in northern areas, southern areas of the Great Lakes region across sections of Illinois, Indiana, and Ohio will see daily high temperatures exceed the 90°F threshold more frequently in a typical year as these areas are already nearer those high temperatures.

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Number of Days per Year Over 95°F

Projected change in number of days per year that exceed 90°F by 2041-2070 as compared to the 1971-2000 period, assuming emissions of greenhouse gases continue to rise (A2 scenario). While temperatures are rising faster in northern areas, the most significant increases in the number of days exceeding the 95°F threshold will remain confined to southern areas. Some locations, however, such as Chicago and Toledo, may see more than two weeks of dangerously hot days per year by mid-century.

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Number of Days per Year Falling Below 32°F

Projected change in number of days per year that fall below 32°F by 2041-2070 as compared to the 1971-2000 period, assuming emissions of greenhouse gases continue to rise (A2 scenario).  The Eastern Upper Peninsula and Northern Lower Michigan, areas that may see the greatest changes in average temperature, may also experience the greatest decrease in overnight low temperatures, reducing the number of days falling below freezing.

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Change in Frost-free Season Length

Projected change in the length of the frost-free season (the growing season), measured in days, by 2070-2099 as compared to the 1971-2000 period, assuming emissions of greenhouse gases continue to rise (A2 scenario). The frost-free season is the period between the last spring freeze and the first fall freeze. The Eastern Upper Peninsula and Northern Lower Peninsula of Michigan may see the greatest changes in frost-free season, as these areas currently have short growing seasons. As winters shorten, the typical year at the end of the century may see 1-2 months less of freezing temperatures in some areas.

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Change in Cooling Degree Days

Projected change in cooling degree day units by 2070-2099 as compared to the 1971-2000 period, assuming emissions of greenhouse gases continue to rise (A2 scenario). Cooling degree days are not actually measured in days, but in the number of degrees that a day's average temperature is above 65°F. Greater increases in cooling degree days generally indicate that air conditioning and energy use are associated with cooling will increase. Already warmer areas to the south will generally see the greatest increases, but areas in the north less-accustomed to heat will see larger proportional increases.

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Total Annual Precipitation

Projected increase in total annual precipitation by 2041-2070 as compared to the 1971-2000 period, assuming emissions of greenhouse gases continue to rise (A2 scenario). Projections of precipitation are highly variable by location, individual model, the timeframe considered. Total annual precipitation is generally projected to increase across the region, but may remain nearly stable or decrease in parts of the Upper Peninsula of Michigan, Northern Wisconsin, and Northern Minnesoata. 

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Number of Days per Year With Heavy Precipitation

Projected changes in average number of days per year experiencing heavy precipitation 2041-2070 as compared to the 1971-2000 period, assuming emissions of greenhouse gases continue to rise (A2 scenario). Heavy precipitation is defined as the 2% heaviest precipitation events in a given area. Projections of precipitation are highly variable by location, individual model, the timeframe considered, and the threshold of precipitation used. Heavy precipitation events are generally anticipated to increase throughout the region. 

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Number of Consecutive Dry Days per Year

Projected changes in average number of consecutive dry days per year experiencing no measurable precipitation by 2041-2070 as compared to the 1971-2000 period, assuming emissions of greenhouse gases continue to rise (A2 scenario). While counterintuitive, the number of consecutive dry days per year could increase in areas also projected to see the largest increases in precipition. Many models project the fall, winter, and spring will get wetter as summers become drier, polarizing the wet and dry periods of the year. Additionally, proportionally more precipitation may fall in heavy precipitation events, leaving more days per year that see little or no precipitation.

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