气候变化领域集成服务门户

Kara Holsopple: How do you know when spring begins?

Alyssa Rosemartin: In some ways, I don t even like that we standardized spring. I feel like springs should be local and cultural. But if we re thinking about understanding broad-scale patterns and trying to track climate across the country in some kind of standard way, we ve settled on this metric, which takes the timing of leaf out and bloom in this suite of lilacs and honeysuckles that we have a long term data set for.

We use a model that researchers developed that uses warmth–accumulated heat, starting January 1st, and the warmer it is each day those values get added together, and you wind up with the date of predicted leaf out of lilacs. Then you accumulate some more heat from that date, and you get the date of predicted bloom in lilacs. 

Holsopple: We have a pretty big listening area. It s all of western Pennsylvania and much of central Pennsylvania. When will spring begin in our area?

Rosemartin: Our model predicts that spring has already arrived in parts of southeastern Pennsylvania, south-central Pennsylvania, and a little strip of Fayette County, Pennsylvania, and not further north.

We have a 6-day forecast, so if we think that spring is going to pop according to our model in the next six days — but I checked and, you know, with this nor easter and cold front that s coming through, we re not seeing additional warmth in the next week. So I expect that spring will spread across the rest of western Pennsylvania–I don t want to say anything more specific than a week–a week from now or more.

Spring is Here, But Is Nature in Sync?

Holsopple: How does the onset of this year s spring, where it already has happened, compare with past years? 

Rosemartin: This is the earliest spring on record in a number of places across the country. The spring of 2023 is definitely an extreme example in a number of places east of the Mississippi.

Big swaths of North Texas are seeing the earliest spring on record. For the Philadelphia area, 2023 is the earliest spring on record. That little strip of Fayette County is the earliest on record. Certainly, the West is cooler than usual this year.

There s a big east-west divide where there have been colder fronts in the West. So the West is delayed compared to normal but not extreme — it s just sort of behind usual, but not by a dramatic amount.

And then parts of the rest of the Southeast, some isolated areas, are seeing also the earliest spring in 40 years, and others are seeing a sort of typical early spring, the kind of spring they might see every 5 to 10 years.

Holsopple: Is this early onset in some of these locations a trend, or is this year just really atypical?

Rosemartin: If we look back at the long-term record, either back to the 1950s, at the observational data, or even we can use a different temperature data set and look at our model all the way back to 1900, we see for sure the fingerprints of climate change.

Spring is getting earlier when you step back and look at 40, 50, 60, and more years of data together. Just like with any other extreme event, like a big hurricane, you can t easily point to climate change as causing this particular extreme. So we tend to say that climate change is loading the dice and making springs like the spring of 2023 more likely. 

Holsopple: What could these early springs mean for animals and plants that are responding to or adapting to climate change? 

Rosemartin: We re seeing, in general, a lot of flexibility where plants are advancing their timing to meet the early spring. And this can have positive effects, where they re able to have an extended growing season, but also negative effects.

One is related to species interactions. So if a bird that depends on a caterpillar is migrating at the same time, but the caterpillar feeds on the trees, and the whole thing is over before the bird gets back, the bird is going to have trouble feeding its young.

We definitely have concerns when species aren t all following the same cues, like when some are paying attention to daylight, and others are paying attention to temperatures.

There are also invasive species, like Japanese knotweed or wild parsnip, which tend to be more opportunistic and more able to take advantage of the early springs than native species. And so, a number of studies have shown that climate change-induced earlier springs favor invasives over natives. They just make that problem even more difficult to tackle. 

Holsopple: How can the information that s collected about the onset of spring be used by scientists or conservationists? 

Rosemartin: We have partners who use the information on the timing of spring, both the general trends over time and the forecasts, to help plan their monitoring or management seasons. Some state parks or national parks have staff that go out to try to find rare plants in bloom, and if they know that things are shifting earlier, they ll adjust their monitoring time to look earlier.

Obviously, the media blitz in the spring, I think it just helps people feel like, Yeah, it did feel like an early spring and how much earlier than usual.

And so, even though there are limitations of the standard we talked about, it also has this really great ability to help us compare what we see and observe anecdotally to a standard measure and contextualize it. 

Holsopple: It s kind of hard to know how to feel about early spring, as a reporter, and just a person who lives here. It feels great to have warm, sunny weather in Pittsburgh, but it also feels like, is this right? Like, should we be celebrating this?

Rosemartin: Working on climate change for more than a decade now, it s just sad and hard. So many parts of it are unredeemed.

And so I feel like when there is a little silver lining, like when we can get a little bit of a longer growing season or grow a plant somewhere that we couldn t before — just first of all, noticing, just being with the change and not putting a value judgment on it right away, and then taking advantage, enjoying the parts of it that are nice and being conscious of the parts of it that are more troubling.

I think it s beautiful and restorative to be out observing plants and that we can enjoy the pieces of it that feel good and that helps us start tomatoes earlier or enjoy flowers earlier.

Alyssa Rosemartin is the partner application specialist with USA National Phenology Network.

Nature s Patterns Hold Clues to How Fast the Climate is Changing