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"Goldilocks days" and a warming climate

A mild weather day
Emma Winowiecki
Michigan Radio
Researchers say that mild weather days - like this one in Northern Michigan - are decreasing globally.

2016 was the hottest year on record.

When we talk about climate change, we usually talk about extreme weather events: extreme heat, drought, flooding. But scientists have also studied what’s likely to happen with the best weather days. Days that are not too hot, not too cold, or humid or rainy. Just right.

Sarah Kapnick is a research physical scientist with the National Oceanic and Atmospheric Administration, and an author of a new studyin the journal Climatic Change.

She says they defined mild weather days - what she refers to as the “Goldilocks of days" - like this:

“Not too hot, not too cold. Almost no precipitation. And low dew point temperature, which is a measure of humidity. The exact temperature range is 64 to 86 degrees Fahrenheit, and with a dew point below 68 degrees Fahrenheit.”

Kapnick’s study projects that the days with mild weather will decrease by four days a year globally within the next two decades. And by the end of the century, the study projects there will be ten fewer mild weather days per year.

"If you actually look at individual locations across the globe, however, the changes are more dramatic," she says. "So some places have increases of mild weather days, whereas other places actually have decreases.”

In the Great Lakes region, Kapnick says this phenomenon is most likely to affect spring, summer, and fall weather - with more mild days in the spring and fall, and fewer in the summer.

What these changes could mean

More warm days in the spring and fall could be great in some ways. But it could also be disastrous, like in 2012, when an abnormally warm, early spring followed by a number of hard freezes wiped out the cherry crop in Michigan.

Kapnick says fewer mild weather days in the summer could have other consequences.

“Heat stress on people is a very big health hazard. That happens in the summer, when we are seeing the loss of mild weather days that might otherwise break up hot weather days or humid days," she says.

And warmer days in the spring can help fuel algal blooms.

Kapnick notes these changes are already happening. Data from NASA show that from 2000 to 2015, there was a loss of 2.5 mild weather days.

“This research also shows that in the future, we will see less mild weather days in the next two decades and we will see even less by the end of the century," she says. "Globally and for the Great Lakes region, we’re seeing the losses of these mild weather days.”

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Rebecca Williams is senior editor in the newsroom, where she edits stories and helps guide news coverage.
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