Climate Change in Minnesota: An MPR News special report

Minnesota is warmer than it used to be. Rain falls in bigger downpours. Hay fever sufferers have a longer sneezing season, and the ticks that deliver Lyme disease are expanding their range. Red maple trees are moving north. So are purple finches. Moose numbers have shrunk.

Without question, the state's climate has changed in recent decades. And that's had an impact on the lives of its wildlife, its plants, its people.

1. It's warmer

From 1895 to 1970, Minnesota's average temperature rose about one tenth of a degree every decade. But since then it has risen more rapidly, about half a degree every decade. Create your own charts at the National Climate Data Center.

2. Winters are warming faster

The average December-February temperature has been going up more quickly, by about 1 degree per decade since the 1970s. Overnight lows also have risen faster than the overall average.

3.Cloquet, Milan and Rochester show the trend

Changes in climate are measured over big areas and many years. But here are three Minnesota examples of rising average minimum January temperatures. Thirty-year averages are important measures for climatologists, and they are re-calculated at the end of each decade.

4. Cold nights decline at Pokegama Dam

At Pokegama Dam near Grand Rapids, between 1887 and 1936 there were an average of 10 nights a year that got below 30 degrees below zero. Since then, the average has been 3 nights a year. In fact, over just the past two decades, the average has been about 1 night a year.

5. North warms faster

An island around Hibbing and Grand Rapids has experienced an average temperature increase greater than that seen almost anywhere else in the nation.

In that area the average temperature in the past two decades is more than 3 degrees higher than the average during the first part of the 20th century. That kind of small-area difference is hard to explain, climate scientists say. But the general trend of northern Minnesota heating more quickly than southern Minnesota reflects a global pattern in which the Arctic and northern latitudes warm faster. National Climate Assessment.

6. It rains more (part 1)

Statewide, average precipitation remained pretty flat from 1895 to 1970, (including a very dry period in the 1930s), but it has been rising since then by about a third of an inch a year every decade. Create your own charts at the National Climate Data Center.

7. It rains more (part 2)

Here's another way to see that increase. Rainfall varies across Minnesota, but all of the state now gets an average of at least 20 inches a year, something that wasn't true in the last century. And the portion of the east that gets more than 30 inches a year is much larger than it was a century ago.

8. It rains more (part 3)

The National Climate Assessment showed that increase this way, measuring the percentage change between two periods, 1901 to 1960 and 1991 to 2012. The biggest increases, shown in dark blue, are in the southeast, central and northwest.

9. It rains more in Waseca

To cite just one example, between 1941 and 1970 the city of Waseca received just under 30 inches a year. Between 1981 and 2010 -- the most recent "30-year normal" that climatologists examine -- the average was nearly 36 inches a year.

10. Mega-rains are more frequent

Climate scientists studying Minnesota say one of the most important shifts in climate has been the severity and frequency of storms.

Measurements get complicated, but far more really big storms -- defined as those in which at least 6 inches of rain fall over an area of 1,000 or more square miles and the core of the storm generates at least 8 inches of rain -- have hit in recent years. Details on the storms.

11. Big storms generate more rain

Another way to look at the big-storm phenomenon is that 37 percent more rain falls as the result of heavy storms than was true 50 years ago. This increase is more pronounced in the Midwest and Northeast than in the rest of the United States. The map represents the increase from 1958 to 2012 of the amount of rain that falls in very heavy storms.

(Note: The Minnesota figure matches the figure for the Midwest overall.)

12. Southern Minnesota smacked 3 times

In particular, some climate scientists find it telling that three of the mega-rains were extremely heavy - considered 1,000-year storms - and took place in pretty much the same area in southern Minnesota. That could be evidence of stronger and more frequent low-level jet streams approaching from the Gulf of Mexico and bringing more moisture at different times of year than they used to.

13. Ice melts earlier

So what impacts of these changes are visible?

To start with something simple, the ice goes out on Minnesota lakes earlier in the spring. This is the trend for Lake Osakis in central Minnesota, for which the state has the longest set of records. In the past century and a half, the orange trend line shows that the average ice-out date has gotten about a week earlier.

14. Growing season grows longer

From 1870 to 1970 the growing season in the Twin Cities (the number of days between the last spring frost and the first fall frost, when frost is defined as air temperature at or below 32 degrees) was pretty stable. Since then the average growing season has gotten several weeks longer.

15. Hardiness zones move north

Changing temperatures have an impact on what farmers and gardeners can grow, of course. U.S. Department of Agriculture measurements show, for example, that zones delineating what plants might survive the coldest temperatures in a given area have moved north. Plants that once worked no farther north than Iowa are now successful in southern Minnesota.

16. Allergy season lengthens

They also mean allergies have become annoying for a longer period each year, one of a number of health impacts that health experts worry about. The ragweed pollen season is three weeks longer in the Twin Cities than it was 20 years ago. The growth in the ragweed season has been even greater farther north. Warmer temperatures are a factor, but researchers also think some plants are producing more pollen because there is more carbon in the atmosphere. Other climate change indicators from the U.S. Environmental Protection Agency.

17. Snow season ends sooner

Snow tends to disappear earlier in the spring.

Between 1960 and 1980, on the left, about three-quarters of the state was covered with two to 20 centimeters on average in early April. On the right, for the years 1980 to 2000, only about half the state had that much snow.

One implication has been an apparent decline in Minnesota of lynx, which need deep snow to compete, and a subsequent increase in bobcats. Another is that land barren of snow is darker and tends to heat more quickly.

18. Home, infrastructure damages rise

The insurance industry has pointed to increasing claims for hail and other storm damage in Minnesota. While this seems consistent with greater precipitation severity, some scientists express skepticism that it truly can be attributed to climate change.

Other factors, like development over more land area, could be significant. But there is no question that cities and property owners alike have dealt with major natural disasters in recent years that could be related to climate change. The 500-year flood in the Duluth area in 2012 is the most often cited, resulting in $108 million in damage to public and utility infrastructure.

19. Lyme disease spreads

In the natural world, the changing climate translates into making some regions more or less hospitable to wild plants and animals. The area where Lyme disease has been reported has gotten bigger, for example.

Lyme disease is a health problem known as vector-borne. The "vector" is the blacklegged (deer) tick, and it is showing up in wooded regions where it was not previously found. More health information (PDF).

20. Aspen, tamarack die

Aspen is the most widely distributed tree species in North America, but scientists have found a decline in aspen in this century in Minnesota and elsewhere. This apparently is the result of changing precipitation patterns, increased temperatures and insect defoliation.

Also prompting concern is a decline in tamarack in northern forests. As with aspen, changing climate patterns have made tamaracks vulnerable. Those changes also have encouraged populations of the eastern larch beetle, which attacks the tamaracks.

21. Maples move

In other cases trees are moving, not individually, of course, but en masse. The center of the range has moved many miles for several species since the 1800s.

Minnesota's maple trees have moved north and east. In the 19th Century the densest stands were in central Minnesota. Now those areas have become less dense and areas farther north, even into the boundary waters, have more dense maples.

22. Moose decline

Climate also seems to be affecting the world of mammals and birds. The range for moose is smaller than it was 100 years ago and the population has dwindled, particularly in recent years.

The decline is thought to be related to a changing climate, both warmer winters that allow ticks to extend their range and more humid summers that put pressure on moose.

23. Birds move north

Birds have also experienced range changes.

Experts are cautious about causes, but where birds live tends to be related to temperature. The center of the purple finch range, for example, has shifted northward by hundreds of miles over the past 40 years or so. In fact, that shift and others like it might be contributing to a measured change in another species, the sharp-shinned hawk. The hawk is flying south later in the fall and apparently not moving as far south as it used to.

As finches and other species move north, the hawk, one of the many seen at Duluth's Hawk Ridge each fall, may have less need to fly south for food. So its migration south "stops short" more than it used to.

That's just one example of how intertwined many climate-change-related impacts can be.

Bonus symptom to watch: Is it muggy in here?

Scientists differ on the significance of how humidity might have been changing in recent years. Global trends vary, and overall average humidity in the Twin Cities has not increased significantly. But some scientists point out what seems like an upward trend in muggy days. This chart shows the number of hours in a given year during which the dew point has been above 70 degrees.

The dew point is the temperature at which water in the air condenses, and days feel particularly uncomfortable when it rises above 70. High dew points, not higher temperatures, have been the main contributor to an increasing number of days on which the National Weather Service declares heat advisories and excess heat warnings. University of Minnesota Extension's Mark Seeley says that is justification for including humidity in the climate change conversation even without more ironclad statistical significance.