Citizen science offers lessons in understanding Fairbanks’ climate

Bright sun shines on green, newly opened birch leaves
Photo by Julie Stricker
Young birch leaves drink in the sunshine after green-up in Interior Alaska. Using decades of data, climate specialist Rick Thoman has come up with a formula to predict the onset of green-up.

Interior Alaska’s long winters are the impetus for a lot of long-running citizen science.

Most famous is the event cooked up in 1917 by a bunch of railroad engineers who bet on the exact minute the ice on the Tanana River would break up. That first bet, which led to the Nenana Ice Classic, netted the winner $800. The 2024 edition had a jackpot of $210,155, which will go to the person or persons who guessed closest to the time—5:18 a.m. April 27—when the ice went out this spring.

The ice classic is a 107-year-long climate record for Interior Alaska. But it’s not the only citizen science effort in Fairbanks, which also boasts multi-decadal data records for predicting green-up, when birch sap will start flowing, and when to stock up on allergy medications for pollen season.

In his fifth annual green-up webinar on April 30, Rick Thoman discussed the history of predicting green-up in Fairbanks.

Green-up doesn’t refer to a particular tree leafing out, said Thoman, a climate specialist with the Alaska Center for Climate Assessment and Policy. It’s on a landscape scale, when a particular hillside on Chena Ridge turns green as seen from the West Ridge of the University of Alaska Fairbanks Troth Yeddha’ campus.  

In the 1970s, UAF scientists Jim Anderson and Bob Elsner started to systematically record green-up on that hillside, with the exception of 1975. 

“From conversations with Jim Anderson many years ago, they probably did note it, but the slip of paper they had it on probably got lost before they compiled it,” Thoman said.

It’s a 49-year record of observations, which Thoman said is a unique set of data. 

Those observations show a great deal of variability, with periods of early green-up and periods showing later dates. The median date of green-up is May 8. This year, green-up was announced late in the afternoon of May 4. 

“We’re running two weeks ahead of last year and about a week behind the record early green-up of 2016,” Thoman said on April 18. Charts showing long-term trends for the Tanana River breakup and green-up look remarkably similar. 

“Green-up is about a week earlier than it was historically,” Thoman said. “That tracks with breakup.”

Green-up starts first on south-facing lower hillsides, and spreads more quickly downhill. Thoman and meteorologist Ted Fathauer saw this as a reaction to daily high temperatures. 

Spring precipitation isn’t an important factor in green-up. In fact, Thoman said, spring in Fairbanks is typically dry. But with a season’s worth of snow melting, there is plenty of moisture for the trees to use. 

In the 1990s, Thoman and Fathauer began working on a way to forecast green-up using easily available climate data, such as high temperatures and solar input. A few years later, Jan Dawe, who leads OneTree Alaska at UAF, suggested that a similar model could be used to predict the rise of birch sap, which occurs weeks before green-up. OneTree’s Birch Sap Collaborative is another project with a great deal of input from the public.

“This has been an ongoing and evolving work for 25 years,” Thoman said.  

Thoman’s green-up formula takes the sum of the daily high temperatures above freezing, beginning on March 1 and adds two variables that give weight to really warm temperatures and to the increase of solar input as spring progresses. 

This formula gives him a window he calls the green-up zone, which he is able to predict weeks ahead of time. While it is designed to predict green-up on southeast slopes in Fairbanks, Thoman said it also works fairly well in Delta Junction and in Anchorage, for birch and aspen trees. He was asked to see if it could calculate green-up in central British Columbia, but it didn’t work at all. 

When green-up occurs, it brings some changes with it, beyond the color of the leaves. It’s important to birch and aspen biology. That change affects the birch sap, which is no longer useful for human tappers. It also signals a seasonal change in diet for moose, who are able to switch from the sticks, twigs and shrubs available in winter to green and leafy foods. 

Green-up also affects humidity and climate, Thoman said. Once the leaves start to unfurl, they start the process of transpiration, which is the movement of water through a plant and its evaporation through leaves. That raises the local humidity, which fuels afternoon showers and,  later,  thundershowers. 

And, the emergence of birch leaves means pollen isn’t far behind. Peak pollen usually occurs two to six days after green-up, depending on temperature, Dawe said during the green-up webinar. In 2020, an exceptionally warm year, the pollen exploded right after green-up and set a worldwide record that was nearly twice as high as the previous record.

High temperatures reached 82 and 80 degrees on the two days after green-up that year, which had an unexpected effect, Dawe said.

Ronda Schlumbohm, a Salcha Elementary School teacher who works closely with Dawe on projects involving birch trees, planted seeds harvested from the OneTree Alaska Long-Term monitoring plot later that fall so her students could grow trees. Not a single seed germinated that year. In 2023, seeds that were collected from the same trees did germinate.

“The T-field research plot is a seed orchard,” Dawe said. “We can collect seed year after year from the same group of trees and see how the seeds’ viability varies year by year. Each year that we harvest and test seeds, the data become more valuable when viewed with an eye to the weather they’re experiencing.”