First thing in the morning, Amanda Joly records the humidity, temperature and rainfall at the Blue Hill Observatory and Science Center south of Boston.
But each year, as spring gives way to summer, she takes one extra measurement. She bends down to assess the fruit hanging from a wild blueberry bush next to the other instruments.
The bush has grown here since the observatory’s founding in 1885. And for 141 years, without missing a season, observers at Blue Hill have recorded the date when the first berry ripens. Their decades of data provide a unique picture of the effects of a warming climate, and its impact on one of New England’s favorite summer treats.
At the turn of the 20th century, the first blueberry was typically ready to eat in the last days of June. Today, the berries are ready a week earlier on average, the records show.
“The data we observe here are consistent with changes that are occurring around the globe,” said Michael Iacono, Blue Hill’s chief scientist “ Our [average] temperature, for example, has changed here about five degrees Fahrenheit since the 19th century.”
Fruit ripens in response to temperature, sunlight and rainfall conditions during the spring. As climate change disrupts weather patterns, plants respond.
“ Everything is interconnected,” Joly said.
While other climate indicators are tracked on dials or gauges, this one involves a more human touch: a taste test.
This year, the blueberry was judged ripe on June 24 by Chief Observer Matthew Douglas. He described it as not too sweet, not too tart.
“Just kinda in between,” he said.
Perched atop Great Blue Hill, the observatory offers soaring views of Boston’s skyline and surrounding suburbs. It is home to the longest continuous weather record in the country, its leaders say. Federal agencies and researchers studying climate and meteorology rely on its data.
Blue Hill scientists haven’t fully analyzed or published their blueberry data, so they can’t say for sure that warmer springs cause the fruit to ripen earlier. But there’s wide scientific consensus that climate change is affecting plants’ seasonal calendars.
“Winter’s shrinking, and we see as a consequence plants and animals largely undergoing their seasonal transitions — especially spring and summer — earlier than they used to in previous decades,” said Theresa Crimmins, director of the USA National Phenology Network, a group that monitors data on how wildlife reacts to seasonal changes.
A record that goes back as far as the blueberry notations at the Blue Hill Observatory is hard to come by, she said. She called the data “phenomenal.”
Richard Primack, a Boston University biologist, studies the effects of climate change on plants, insects and birds, and has used Blue Hill’s data in his research. He focuses on the area around Walden Pond in Concord, where he’s observed blueberries and other species fruit early.
“The blueberry’s especially an important example because the blueberry is one of the absolute favorite fruits of not only people, but also birds,” said Primack. If the bush ripens too early, migratory birds have no food source when they arrive in the spring.
For many New Englanders, blueberries are a beloved rite of summer. Residents look forward to picking the berries from their bushes for pies and jams. In Maine, lowbush “wild” blueberries— distinct from the conventional blueberries on supermarket shelves— are considered a heritage food, akin to lobsters for their cultural significance. Nearly all the wild blueberries sold in the U.S. come from the barrens of Maine.
The practice of managing wild blueberries has been passed down through generations in Maine. Families could expect the berries to ripen at almost exactly the same time every year, but that’s becoming harder to predict, said Lily Calderwood, a wild blueberry specialist at the University of Maine.
“Absolutely, we do see that our harvest time has moved forward by about two to three weeks,” Calderwood said. “Farmers basically have to be prepared for anything, and that is very expensive.”
During a warm spring, blueberry bushes may flower early. But a cold snap can cause the flowers to freeze off and die. That means no blueberries.
“It’s just hard to see all of those beautiful white blossoms just turn brown and shrivel up,” said Ashley Field, co-owner of Fields Fields Blueberries in Midcoast Maine. The farm lost 80% of its crop to a frost three years ago.
To adapt to the changing climate, some farmers have installed irrigation systems, which Calderwood said can help prevent flowers from dying in a frost, and reduce losses from droughts.
Back at Blue Hill Observatory, Iacono and Joly examined a graph of their blueberry bush’s ripening dates from the past 141 years. The lines waved up and down in what appeared to be a cyclical pattern. But the larger trend was unmistakable: On average the first berry is ripening earlier than before.
“ We’re kind of on a period where it’s getting a little bit later again,” said Iacono, a trend he described as common with many weather phenomena, although researchers aren’t sure why.
“ It’s part of the natural variability that we’re trying to understand,” he said.
Blue Hill’s data is important because of the continuity of the measurements, said Joly. Observers have tracked berries on the same bush, in the same location, tested in the same way, for 141 years.
“It’s an apples-to-apples comparison,” she explained.
Iacono couldn’t resist grabbing some low-hanging fruit.
“As we like to say, it’s a blueberry-to-blueberry comparison,” he joked.
This article was originally published on WBUR.org.
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