MINNESOTA

   

Figure 1

Figure 1: Observed and projected changes (compared to the 1901–1960 average) in near-surface air temperature for Minnesota. Observed data are for 1900–2014. Projected changes for 2006–2100 are from global climate models for two possible futures: one in which greenhouse gas emissions continue to increase (higher emissions) and another in which greenhouse gas emissions increase at a slower rate (lower emissions). Temperatures in Minnesota (orange line) have risen about 2°F since the beginning of the 20th century. Shading indicates the range of annual temperatures from the set of models. Observed temperatures are generally within the envelope of model simulations of the historical period (gray shading). Historically unprecedented warming is projected during the 21st century. Less warming is expected under a lower emissions future (the coldest years being about as warm as the hottest year in the historical record; green shading) and more warming under a higher emissions future (the hottest years being about 11°F warmer than the hottest year in the historical record; red shading). Source: CICS-NC and NOAA NCEI.

Minnesota is located in the interior of North America, resulting in large temperature variations across the state, where winters are cold in the south and frigid in the north and summers are mild to occasionally hot in the south and pleasantly cool in the north. The lack of mountains to the north or south allows for incursions of bitterly cold air masses from the Arctic as well as warm, humid air masses from the Gulf of Mexico, further increasing the range of conditions that can affect the state. The summer is characterized by frequent warm air masses, either hot and dry continental air masses from the arid west and southwest or warm and moist air that pushes northward from the Gulf of Mexico. The summer is also punctuated by periodic intrusions of cooler air from Canada, providing breaks from summer heat. Temperature extremes have ranged from as low as -60°F (Feb. 2, 1996, Tower) to as high as 115°F (July 29, 1917, Beardsley). Minnesota’s wide range between highest and lowest temperatures is the third largest of non-mountainous states. Also, Minnesota is located on the eastern edge of the transition zone between the humid climate of the eastern United States and the semi-arid Great Plains, exemplified by large differences in average precipitation across the state. Snowstorms are a normal part of the winter and early spring climate, with average annual snowfall ranging from 40 to 60 inches over most of the state.

Temperatures in Minnesota have increased more than 2°F since the beginning of the 20th century (Figure 1). Since the year 2000, Minnesota has experienced 7 out of its 10 warmest years on record. This warming has been concentrated in the winter while summers have not warmed as much. The summer warming has been mostly an increase in nighttime temperatures, with the coolest nights of summer becoming warmer. By contrast, summer daytime high temperatures have increased very little. This is reflected in a below average occurrence of hot days (maximum temperature above 90°F; Figure 2a). There is no overall trend in warm nights (minimum temperature above 70°F) (Figure 2b). The winter warming trend is reflected in a decline in the number of very cold days (maximum temperature below 0°F) over the past two decades, with a historic low occurring during the 5-year period of 2000 to 2004 (Figure 2c). The date of lake ice-out has also been getting earlier in the last few decades (Figure 3).

Average annual precipitation has been above the long-term average for the past 25 years (Figure 4). Likewise, the number of extreme precipitation events (precipitation greater than 3 inches) has been above the long-term average over the past 30 years, with the record 5-year number occurring during the period of 1990 to 1994 (Figure 2d). Average annual precipitation, including rainfall and the water equivalent found in snowfall, ranges from 18 inches in the far northwest to more than 32 inches in the southeast. Nearly two thirds of the average annual precipitation occurs during the growing season (May through September). However, occasional drought is a natural feature of the climate, occurring when anomalous circulation patterns bring in dry air from the interior of North America.

 

Figure 5

Figure 5: Number of excessive heat events by county from 1995 to 2002. Excessive heat events occur more frequently in counties located in central and southern Minnesota. Source: Minnesota Climate Change Vulnerability Assessment. Data from NCEI’s Storm Events Database.

Between 2000 and 2012, extreme weather events (including extreme drought, summer heat waves, severe storms, heavy rain and flooding, and tornadoes) caused an estimated $4.3 billion in damages to property. In general, thunderstorms cause more property damage than any other extreme weather type in Minnesota. The annual frequency of thunderstorm days is roughly 45 days in the southern part and 30 days along the northern border. Due to Minnesota's northern location, heat waves are infrequent, but they can have severe consequences as the population is less acclimatized to these events. Since 1995, excessive heat events have occurred most frequently in the central and southern counties (Figure 5). Since 2000, the number of very heavy rains (6 inches or more in a day) have been 2-3 times more frequent than in the 20th century.

Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century (Figure 1). Even under a pathway of lower greenhouse gas emissions, average annual temperatures are projected to most likely exceed historical record levels by the middle of the 21st century. However, there is a large range of temperature increases under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records. Increases in the number of extremely hot days and decreases in the number of extremely cold days are projected to accompany the overall warming.

Annual average precipitation is projected to increase, with increases most likely occurring in the winter and spring (Figure 6). This is part of a large area of the Northern Hemisphere in the higher middle latitudes projected to see increases. Increases in intense rainfall are also expected. Despite these increases in precipitation, it is possible that future droughts will be more intense because of higher temperatures, which will increase the rate of loss of soil moisture. In 2007, 24 counties in Minnesota received federal drought designations, while 7 counties were declared flood disasters. Again in 2012, 55 counties received drought designations at the same time that 11 counties declared flood emergencies. Recent events demonstrate the likelihood of simultaneous increases in both flooding and drought severity within the state.

Resources

1. Kunkel, K.E, L.E. Stevens, S.E. Stevens, L. Sun, E. Janssen, D. Wuebbles, S.D. Hilberg, M.S. Timlin, L. Stoecker, N.E. Westcott, and J.G. Dobson, 2013: Regional Climate Trends and Scenarios for the U.S. National Climate Assessment. Part 3. Climate of the Midwest U.S., NOAA Technical Report NESDIS 142-3, 95 pp. [URL]
2. MDH, 2014:  Minnesota Climate Change Vulnerability Assessment 2014, Minnesota Department of Health, Minnesota Climate & Health Program, Environmental Impact Analysis Unit, 100pp. [URL]
3. MDH, cited 2016: Climate change overview: Climate change in Minnesota climate and health profile report, Minnesota Department of Health. [URL]
4. Minnesota Historical Society, cited 2016: Natural disasters in Minnesota, State Historic Preservation Office. [URL]
5. MN Department of Natural Resources, cited 2016: Climate frequently asked questions. [URL]
6. MN Department of Natural Resources, cited 2016: Climate’s impact on water availability. [URL]
7. MN EQB, cited 2016: Minnesota and climate change: Our tomorrow starts today, Minnesota Environmental Quality Board. [URL]
8. NOAA NCEI, cited 2015: State Climate Extremes Committee (SCEC), Records, National Oceanic and Atmospheric Administration National Centers for Environmental Information. [URL]
9. NOAA, cited 2016: Climate at a Glance: U.S. Time Series, published October 2016, retrieved on October 18, 2016, National Oceanic and Atmospheric Administration National Centers for Environmental Information. [URL]
10. NOAA, cited 2016: Climate of Minnesota, National Oceanic and Atmospheric Administration. [URL]
11. Tompkins, F. and C. Deconcini, 2014: The climate change connection to U.S. public health, Fact Sheet, World Resources Institute. [URL]
12. Vose, R.S., D.R. Easterling, K.E. Kunkel, A.N. LeGrande, and M.F. Wehner, 2017: Temperature changes in the United States. In: Climate Science Special Report: Fourth National Climate Assessment, Volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 267-301.