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Minnesota may gain "mild" days in spring, fall

DULUTH — For years the discussion about global climate change has been about how warm it's going to get in many areas, or how wet, how dry or how stormy.

But scientists at the National Oceanic and Atmospheric Administration and Princeton University wanted to answer a different question: How will worsening climate change impact nice weather?

Their answer, for much of the United States and indeed across the Earth, was that there will be far fewer "mild days" in the near future than there has been in the recent past.

But, for Minnesota, the study found that springs and falls will see considerably more mild days as winter has a shorter impact.

NOAA's definition of "mild" is the kind of day you'd want to be fishing, enjoying an outdoor ball game, having an outdoor wedding or picnic — between 64 and 86 degrees with less than a half-inch of rain and dew points, or humidity, in the comfortable range.

The new research, published in the journal Climatic Change and made public Wednesday, projects the number of mild days globally will decrease by 10 to 13 percent by the end of the century because of climate warming from the build-up of human-caused greenhouse gasses in the atmosphere.

The current global average of 74 mild days each year will drop by four days by 2035 and 10 days by 2100, the study found.

But computer models predict we'll see between 5 and 10 additional days in the "mild'' range each fall and again each spring. That echoes trends already documented showing longer falls and earlier springs, with ice over later and ice-out significantly earlier in Minnesota and Wisconsin than just 50 years ago.

In summer, it appears the Northland will see a few less mild days, likely because of higher heat and humidity. Of course, none of those "mild" days will happen in core winter.

That's a far cry from much of the U.S. that will see far fewer "mild days'' — not because it will be colder, but because it will be too warm, too rainy or far too humid due to the increasingly warmer atmosphere.

Much of the Midwest, mountain west and mid-Eastern states will see far few "mild'' days each summer, thanks to higher temperatures, uncomfortable humidity levels and more big rainstorms.

The global average of 10 percent fewer nice days "masks more dramatic decreases in store for some areas."

While much media attention has been given to climate change impact on extreme weather — floods, hurricanes, etc., little attention had been focused on how worsening climate change will impact the livability of some areas. And it appears some areas will be far less livable.

The Washington, D.C., area already is known for its unusually humid and uncomfortable summers. By the next century, the study hints, summers there may become unbearable, with 15 fewer nice days.

"Extreme weather is difficult to relate to because it may happen only once in your lifetime," said Karin van der Wiel, a Princeton researcher at NOAA's Geophysical Fluid Dynamics Laboratory. "We took a different approach here and studied a positive meteorological concept, weather that occurs regularly and that's easier to relate to."

The study shows the largest decline in mild weather occurring in tropical regions because of rising heat and humidity. The hardest-hit areas are expected to be in Africa, Asia and Latin America, where some regions could see 15 to 50 fewer days of mild weather annually by 2100.

Those are also areas where research shows economic damages due to climate change. The loss of mild weather days, especially during summer, when they can serve to break up extended heatwaves, also could significantly affect public health, NOAA predicts.

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