Temperature

Temperature in the Great Lakes Region
  • Since 1900, average temperatures have increased by 2.0°F (1.1°C) in the U.S. Great Lakes region.
  • By 2050, average air temperatures are projected to increase by 1.8 to 5.4°F (1 to 3°C). 
  • By 2100, average air temperatures are projected to increase by 3.6 to 11.2 °F (2 to 6.2°C). 
  • Winter temperatures have been rising faster than temperatures during other seasons.
Observed annual temperature departures from averageSince 1900, annual average temperatures have increased by 2.0°F (1.1°C) across the 8 U.S. Great Lakes states, significantly faster than both the national and global rates.
Observed changes in average temperature across the Midwestern and Northeastern U.S. states.Changes in temperature vary by geography within the Great Lakes region, with northern areas experiencing the most warming.

Rising Average Temperatures

Average air temperatures are rising. Since 1900, annual average temperatures have increased by 2.0°F (1.1°C) across the 8 U.S. Great Lakes states. After declining slightly through the first half of the 20th centrury, temperatures warmed by 2.4°F (1.3°C) since 1950 and by 2.9°F (1.6°C) since 1960, significantly faster than both the national and global rates.1

Models project future temperatures will continue to rise by 7.5 to 11⁰F (4.2 to 6.1⁰C) throughout the region by 2100, assuming global greenhouse emissions continue to increase as they have in the recent past.2 1 3 

Geographic and Seasonal Variation

Northern areas of the region have seen the greatest increases in temperature so far and are expected to see the greatest increases in the future.1 3 The rate of warming has been fastest during the late winter with many areas seeing twice the annual rate of warming. This trend is anticipated to hold through the first half of the 21st century. Beyond mid-century, summer and spring temperatures may show greater increases compared to the winter and fall.4 Overnight low temperatures have also increased slightly faster than daytime high temperatures.5

Projected Changes in Temperature for the Midwestern U.S.Projected mid-century changes in temperature for the Midwestern U.S. Figure source: Third National Climate Assessment: Chapter 18: Midwest.

Future Temperatures Depend on Future Greenhouse Gas Emissions

Most of the uncertainty in temperature beyond the middle of the 21st century is due to the global human response to climate change. Projections of future temperature at the end of the coming century vary tremendously based on the rate of future greenhouse gas emissions. Through the next 30-40 years, however, the greenhouse gases already emitted into the atmosphere will continue to drive temperatures higher for decades. By 2050, across high and low emissions scenarios, models project average annual air temperatures in the region will increase between 1.8 to 5.4⁰F (1 to 3⁰C). By 2100, the range from high to low emissions scenarios is greater, with models projecting temperatures will rise between 3.6 to 11.2⁰F (2 to 6.2⁰C).6 7 8 9 Reducing greenhouse gas emissions from the current rate would significantly reduce the warming we experience through the later half of this century. 

Extreme Heat

As average temperatures rise, the chance of extreme summer heat will also increase. The number of days with a maximum temperature greater than 90°F (~32°C) may increase from 15 per year (in 2010) to between 36 and 72 days per year across the Midwest.10 For reference, an event as intense as the 1995 Chicago heat wave could occur as frequently as every other year to three times per year, depending on the emissions scenario.11

Lake Temperatures

The Great Lakes have warmed faster than the nearby air temperature in recent years. Lake Superior summer (July–September) surface water temperatures increased approximately 4.5°F (2.5°C) from 1979-2006, significantly faster rate than regional atmospheric warming. Declining winter ice cover is the largest driving factor. The onset of first ice cover on inland lakes in the region is 6-11 days later than during the middle 19th century and the breakup of ice in the spring is 2-13 days earlier. With shorter winters and open lake water earlier in the spring, the lakes are becoming stratified earlier, allowing the lakes a longer period to warm and amplifying the effects of warmer summer air temperatures.12

Observed change in the frost-free season length in the United States. The Midwestern and Northeastern U.S. experienced an increase in the frost-free season of 9 and 10 days, respectively, from 1958-2012.Observed change in the frost-free season length in the United States. The Midwestern and Northeastern U.S. experienced an increase in the frost-free season of 9 and 10 days, respectively, from 1958-2012.

Shorter Winters and a Longer Growing Season

The period of the year between the last winter freeze and the first freeze of the following winter, often referred to as the frost-free or growing season, has increased by 9 days in the Midwestern U.S. states and 10 days in the Northeastern U.S states, on average.1

The growing season is, of course, critical to agriculture, and numerous studies have examined its behavior over time in the Midwest.13 14 15 Generally, the growing season lengthened by 1-2 weeks throughout the region during the 20th century. The rate of change in the date of the last spring freeze may be more responsible for the overall shortening of winter.14

The lengthening of the growing season will either continue at the current rate or accelerate in the future. Under high emissions scenarios, model projections indicate the growing season will increase by 1-2 months across the region by 2100.9

 

  • 1. a. b. c. d. Walsh, J., and Coauthors, 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. J. M. Melillo, T. C. Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program.
  • 2. Based on the range of projections of CMIP3 A2 and CMIP5 RCP8.5 projections.
  • 3. a. b. Pryor, S. C., D. Scavia, C. Downer, M. Gaden, L. Iverson, R. Nordstrom, J. Patz, and G. P. Robertson, 2014: Chapter 18: Midwest. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, T. C. Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 418-440. 10.7930/J0J1012N.
  • 4. Wuebbles, D. J., K. Hayhoe, and J. Parzen, 2010: Introduction: Assessing the Effects of Climate Change on Chicago and the Great Lakes. Journal of Great Lakes Research, 36, 1-6.
  • 5. Wuebbles, D. J., 2006: Executive Summary Updated 2005: Confronting Climate Change in the Great Lakes Region.
  • 6. Hayhoe, K., J. VanDorn, T. Croley Ii, N. Schlegal, and D. Wuebbles, 2010: Regional climate change projections for Chicago and the US Great Lakes. Journal of Great Lakes Research, 36, Supplement 2, 7-21.
  • 7. Lofgren, B. M., F. H. Quinn, A. H. Clites, R. A. Assel, A. J. Eberhardt, and C. L. Luukkonen, 2002: Evaluation of potential impacts on Great Lakes water resources based on climate scenarios of two GCMs. Journal of Great Lakes Research, 28, 537-554.
  • 8. Scheller, R. M., and D. J. Mladenoff, 2005: A spatially interactive simulation of climate change, harvesting, wind, and tree species migration and projected changes to forest composition and biomass in northern Wisconsin, USA. Global Change Biology, 11, 307-321.
  • 9. a. b. Wuebbles, D., and K. Hayhoe, 2004: Climate Change Projections for the United States Midwest. Mitigation and Adaptation Strategies for Global Change, 9, 335-363.
  • 10. Vavrus, S., and J. Van Dorn, 2010: Projected future temperature and precipitation extremes in Chicago. Journal of Great Lakes Research, 36, 22-32.
  • 11. Hayhoe, K., S. Sheridan, L. Kalkstein, and S. Greene, 2010: Climate change, heat waves, and mortality projections for Chicago. Journal of Great Lakes Research, 36, 65-73.
  • 12. Austin, J. A., and S. M. Colman (2007), Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback, Geophys. Res. Lett., 34, L06604, doi:10.1029/2006GL029021.">
  • 13. Skaggs, R., and D. Baker, 1985: Fluctuations in the length of the growing season in Minnesota. Climatic Change, 7, 403-414.
  • 14. a. b. Robeson, S., 2002: Increasing Growing-Season Length in Illinois during the 20th Century. Climatic Change, 52, 219-238.
  • 15. Linderholm, H. W., 2006: Growing season changes in the last century. Agricultural and Forest Meteorology, 137, 1-14.