Climate change is exacerbating extreme weather events, driving famine, and increasing risk of violent conflict. It could also change our world in subtler ways; for instance, by changing how leaves turn bright colors in the fall. It’s a topic on which there’s not much peer-reviewed research, but one that Jim Salge, foliage expert for Yankee Magazine, couldn’t help but investigate.
Each year, Salge draws on his background in meteorology — and passion for autumn — to pinpoint the best times to visit various New England locations to spot the most vibrant leaves. In recent years, he’s found those patterns have been harder to forecast. He wondered if climate change could be the culprit, since a combination of warm days and cool nights creates the best foliage. Fall days have felt warm, but he suspected nighttime temperatures were staying high.
So he crunched data from the National Weather Service, focusing on daily low temperatures, which usually happen at night. The changes he found were astounding. For instance, there were only five years in all of the 20th century when average September lows rose above 60 degrees in Boston, but already in the first two decades of the 21st century, there have been nine. Meanwhile, Portland, Maine, had its first frost in September for 13 of the 20 years from 1950 to 1970. By the new millennium, it had moved to October, falling in that month every year from 2001 to 2021 except one; that year, it was in November. He found a similar shift in Concord, N.H.
In a recent story for Yankee, Salge combined his findings with his own experience and that of others, even including records kept by a pancake house in the North Country.
The Globe spoke with Salge about his observations and thoughts on fall and whether climate change could hurt New England’s iconic foliage.
Q. How did you get interested in the effects of the climate crisis on foliage?
A. When I moved to New England 20 years ago, I had this idealized notion of what the fall weather was going to be, but increasingly, it’s humid and sticky later and later, like into September.
There would be years where I’d drive up to Pittsburgh in September and the leaves would still be green. That just didn’t seem right, because I’m always looking at these foliage maps of historical averages and they’d say foliage peaks in late September.
Q. Right. And you decided to try to quantify some of those changes and then to forecast what changes we could see in the future when it comes to foliage. How did you set out to do that?
A. I knew I wasn’t going to be able to do some big statistical analysis because that’s not my area of focus. But I can count! So I wanted to look at the numbers of times that a certain thing happened, like how many times low temperatures stayed above 60 degrees in September in Boston, or the number of times the first frost was in September rather than October or November.
I used data from the National Weather Service and compared across a dividing line. So, for instance, I looked at the period from 1990 to 2020, and then I compared it to the 30-year period before that. And I found that in the period after the year 2000 in New England, it just seems like a switch flipped.
I focused on overnight lows. Because days are warming, sure, but overnight lows seem to be consistently 2½ degrees higher in the 1990 to 2020 average than the whole 20th century average.
Q. Broadly speaking, what does this all mean for fall foliage? How are you seeing those shifts play out?
A. Well, there’s very little peer-reviewed scientific data analysis of fall color. But we do know the biggest determinants of when the leaves are actually going to turn. We need warm, sunny days to make the reds, and we need crisp, cool nights to kick-start things. If we aren’t having those crisp, cool nights, that means the foliage is going to peak later.
Now, in a changing climate, we’re going to see these wild shifts from year to year, and that makes it hard to really statistically quantify. But on average, we can see trends.
We need warm, sunny days to make the reds, and we need crisp, cool nights to kick-start things. If we aren’t having those crisp, cool nights, that means the foliage is going to peak later.
That shifts growing seasons and it shifts foliage patterns. Our entire speciation of our forest is changing.
A. Take white oaks. Since they prefer warmer conditions, they extend north only into Southern New England. So, northern New Hampshire and Vermont forests are beautiful because they don’t have oak mixed into them, and oak turns later. That means in all those northern forests, the trees turn at once.
But as temperatures get warmer, the question is: Will oaks get a foothold up there? That could change how those forests look. By a lot.
Let’s talk about the sugar maple, which is known to turn bright orange and red. The sugar maple does not extend its range south of New England very much. This is the southern end of their range.
But there’s a good chance in a warming climate that they could be replaced by white oaks. There are tons of white oaks in Boston, but there are very, very few in northern Vermont, northern New Hampshire.
Q. What would that look like?
A. Oaks tend to turn rusty colors instead of really bright, vibrant colors. And again, they turn later in the fall.
You’ll see peak colors with the sugar maple, but the oak will lag behind. You’ll never get that all-at-once, big pop of vibrant color that you see in the northern forest.
Q. That’s sad. You know, in your piece, you of course mention the lack of peer-reviewed data on these trends, but you do draw on anecdotal evidence of these changes. For instance, you mention the records kept by staff at Polly’s Pancake Parlor, a restaurant in Sugar Hill, N.H., that you say is a great spot to see foliage.
It’s kept a record of fall foliage data dating back to 1975, and has noticed peak foliage is arriving later.
A. Oh, yeah! Polly’s is an interesting record. But there’s so many observers. You go up to the North Country it’s clear that foliage means so much to everybody. I’ll go up there and say that I work for Yankee Magazine, and they’ll talk my head off about fall foliage. Regardless of the political connotations of climate change or whatever, people will all seem to say, “Yeah, it seems to be later this year.” Whether or not they draw a connection to the bigger picture, I think people know that fall feels different.
Q. You mention in the piece that climate change is not the only threat facing trees. Talk a little bit about some of the other ones, and what kind of effect they could have.
A. Well the other big one is invasive species. We’ve brought so many plants and bugs from all over the world, and it just seems like if you see an early successional forest — like something that used to be a field, and is maybe like five years grown in — and you just walk through there, instead of the birch trees and the willow trees and things that were native to the area, it just seems to be a lot of honeysuckle and buckthorn and autumn olive.
If those have been the pioneers for the past 30 or 40 years, will those replace some of the well-known New England trees? If we have warmer overnight temperatures and we have invasive species, what will that mean?
Look at the Asian longhorned beetle that attacked Worcester 10 years ago. That beetle has a preference for maple. If those really spread again? Not good for sugar maples!
Q. Doesn’t sound like it!
A. I’ve read that a big reason we have this fall foliage in New England is that the 1938 Hurricane killed so many white pines in the area and that made way for the hardwood forests we know today. So we’ve had less than a hundred years of beautiful fall foliage in New England. The future’s not known.
Q. You end your new piece by saying that climate change could mean foliage changes, which could mean traditions have to change. How do you mean?
A. It’s a beautiful time to be outside. My traditions are going to a hawk watch, going apple picking, going into a corn maze. We’ve built the culture of New England fall around these things. If the temperatures are changing, the timing of these traditions could change. There’s the changes to the foliage, but also, it just feels different to go out leaf peeping in a warmer climate.
Interview was edited and condensed.