In January 2017, days after President Trump moved into the White House, Justin Connelly was at his home in Anacortes, Wash., bemoaning the fate of scientists.
In speeches, the president called global warming a hoax. He vowed to disband the Environmental Protection Agency and withdraw from the Paris climate agreement. Worse, Mr. Connelly feared the Trump administration would purge climate information from government databases.
He wondered: Would scientists resort to using chisels and stone to preserve their findings? Or, perhaps, stitch them into tapestries?
Mr. Connelly’s friend Emily McNeill worked in a knitting store. The two decided (along with Mr. Connelly’s then wife, Marissa) to assemble a kit of colored yarns that knitters could use to create scarves that documented local temperature changes all year.
They would access data reported by the National Oceanic and Atmospheric Administration, which knitters would represent in colors from sunny yellow to fiery red and icy blue. Mr. Connelly and his colleagues called the endeavor the Tempestry Project and, since then, they have sold more than 1,500 kits worldwide.
“We didn’t want this data lost forever,” he said.
Temperature scarves, as they are commonly called, have more than fashion appeal. Laura Guertin, a professor of earth science at Penn State Brandywine in Media, Pa., uses hers as a teaching aid in the classroom. Last year, Erika Zambello, who works for Audubon Florida, a conservation group, began organizing volunteers to record temperature changes at U.S. National Parks.
So far, scarves have been knitted on behalf of 30 national parks, she said, including Glacier Bay and the Grand Canyon. More are on the way. Even Larry Fink, the chief executive of the investment firm BlackRock, recently wore a temperature scarf at the World Economic Forum in Davos, Switzerland, to call attention to the climate crisis.
“It’s a way to start a conversation about climate change that is different,” Ms. Zambello said. “Charts and graphs are fine, but they appeal to an analytic mind-set. This way you can talk about what the colors mean.”
No one can pinpoint exactly when the first temperature scarf emerged but many knitters point to the popularity of the “sky scarf” in the early 2010s.
Lea Redmond, a conceptual artist from Oakland, Calif., began knitting scarves in 2011 that reflected the weather. She did not intend it as a political statement on global warming but a reminder to appreciate nature. “It was about falling in love with the world you live in,” she said. “And if you love it, you will take care of it.”
Scientists, though, had other ideas. Quilts and blankets that track rainfall, air pollution and temperature have been around for awhile.
Ed Hawkins, a British climate scientist, came up with “warming stripes” in 2018, a series of lines of red, orange, white and blue, which he printed on ties, leggings and flip-flops as a visual reminder of long-term warming trends. In 2017, Dr. Guertin was inspired to crochet temperature tapestries to share with her students after seeing a quilt on Twitter.
She brought her tapestries to a class she teaches for nonscience majors. “It was a new way of looking at climate data,” she said.
Her students seemed to relate. One student recalled playing baseball outside in winter. Dr. Guertin said the student’s memory was triggered by the unusually warm colors in the February portion of the tapestry. “I don’t even have to say anything,” she said. “They just understand.”
Dr. Guertin now crochets baby blankets for friends, chronicling the daily temperature of a newborn’s first three months. “They show them to their friends and talk about it,” she said. “I’m turning them into science educators and they don’t even know it.”
The scarves can have different patterns, colors and textures. But there are a few basic concepts. Knitters knit one row per day, matching the color to the daily temperature calculated by NOAA. Some of them use beads to depict rain. Others add a strand of silver yarn for snow.
Scott Rohr is an owner of The Yarnery in St. Paul, Minn. He is concerned about the market for American wool, which, he said, is affected by climate change related to issues of water consumption and land use. The Yarnery offers kits for knitters, with prices ranging from $55 to $125. So far, it has sold about 400, he said.
Ms. Zambello was given a Tempestry kit in 2018. “It excited me in a way no other thing had in the craft space,” she said. “I immediately wanted to set up a Tempestry for the national park system, to show what we knew was changing.”
Whenever a scarf is finished, it is taken to a park and photographed there. Then they are posted on a website Ms. Zambello maintains. She said she hoped to turn the project into a book, with the proceeds donated to preserving national parks. “I want to work together to tell a bigger story,” she said.
Mr. Connelly said there was another byproduct to knitting a warming world that can’t be measured: calm.
“Clearly climate change is a concern and part of the zeitgeist of anxieties today,” he said. “Knitting is a comforting and meditative way to channel all those anxieties.”