In 1879, the USS Jeannette and her crew left San Francisco, headed for the Bering Strait with a dream: to win the race to reach the North Pole. After months of perilous sailing, the Jeannette made it through the strait. But soon after, she got stuck in the grip of ice floes, or sheets of floating ice.

For two years, members of the Jeannette’s crew waited, recording observations about the strange Arctic world around them in the ship’s logbooks: temperatures, barometric pressure, features of the beautiful auroras above them and more. They hoped that the ice sheets would move, releasing the Jeannette and allowing the crew to return to San Francisco. But the ice persisted, and the Jeannette was eventually crushed. She sank to the bottom of the ocean, leaving the surviving members of her crew to trek hundreds of miles across the ice toward safety. Of the 33-member crew that had left San Francisco, only 13 returned.

Today, the Jeannette’s recovered logbooks tell incredible stories about life, death, Arctic temperatures, fear and boredom. The records, which originally existed only in federal archives, are now available to anyone who wants to read them on a website called Old Weather.

Old Weather is a gathering place for more than 4,500 citizen-sleuths who are helping climate scientists map our planet’s ancient weather patterns, for free, one logbook at a time. These volunteers read and transcribe notes from sailors, hoping to map the mostly unknown history of our planet’s weather patterns.

According to Kevin Wood, an Old Weather co-founder, examining the past in this way is key to understanding the earth’s future. As Arctic ice begins to melt at faster and faster rates, scientists need to quickly gain a better understanding of climate change and the impact it could have on humans. By looking at past weather events recorded in old ship logbooks, Wood hopes that he and his fellow scientists can learn more about our planet’s traditional weather patterns, which will help them predict extreme weather events like tsunamis and hurricanes.

“Extreme weather events are, by definition, rare,” Wood said. “So we need to look back to see if that thing has happened in the past.”

For some of the volunteers, their Old Weather work is a noble hobby. For others, it’s a way to fight climate change from their homes. But together, these volunteers have read and transcribed more than 4 million decades-old, often-untouched weather, ocean and sea-ice observations from whaling vessels and federal vessels, like the USS Jeannette, that were active from 1842 to 1950.

“Nearly everything we know about the Arctic and the ocean before we had satellites can be linked to ship logbooks,” said Wood, who’s also a researcher at the Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington. “Logbooks are like a codex — a bound manuscript with thousands and thousands of insights.”

Old Weather is one small part of a massive citizen-science platform called the Zooniverse that hosts dozens of participatory science projects. These projects range from recording bats’ behavioral patterns, to helping computers understand animal faces, to hunting supernovas. After signing up to participate in any Zooniverse project, the network’s volunteers, which number more than 1.5 million, are given access to data sets specific to each project. At Old Weather, this data generally takes the form of handwritten logbook pages that volunteers transcribe onto an online form which converts the information into coded data points. Lucy Fortson, a founding member of the Zooniverse project, said each page is read by an average of at least four volunteers to ensure that the resulting data is accurate, a concept that social scientists call the “wisdom of the crowd.” On Old Weather, Wood said, scientists are particularly interested in barometric pressure and temperature data, which helps them see Arctic weather patterns that could be intrinsic to our climate system.

As of the beginning of this year, volunteers have transcribed more than 480,000 pages of logbooks. Wood said that this work would have been impossible for a few scientists to tackle alone and that there are still millions of observations yet to be recorded. Before accessing this data, scientists had little record of the history of our planet’s weather because most of it was archived and handwritten.

While Old Weather volunteers have access to millions of weather observations, Wood said few logbooks are more scientifically interesting than those from the USS Jeannette because the logs have provided previously unknown details about aurora behavior, temperature and the experience of being lost at sea.

And the new observations could help solve the mysteries of the ship itself. Recently, Wood uncovered new details about ice deterioration that suggested that the Jeannette’s wreck might still exist. And his research suggests that the wreck might even be discoverable, which was previously considered impossible.

“We originally thought the ship was destroyed by ice,” Wood said. “But I did some background research on ice keels and how deep they go, and it turned out that if the [Jeannette] wreck wasn’t hit by something larger, it could still be there.”

Based on these findings, Wood said, scientists and explorers took a trip to the Arctic last year in search of the Jeannette. Unfortunately, ice remained over the targeted location for the entirety of their visit, so they weren’t able to dive. But, he said, they hope to keep the search going next year.

Volunteer research on the Jeannette has also contributed to several published scientific studies about Arctic weather patterns, volcanic behavior and auroras: “Going with the Floe,” an article based on the Jeannette’s logbook findings, was published in Astronomy & Geophysics in April 2016. A study based on Old Weather research about Arctic ice patterns was published in the International Journal of Climatology as well.

Stories like that of the USS Jeannette aren’t uncommon in the Zooniverse. Fortson, a professor at the University of Minnesota’s school of physics and astronomy, recalled another, about citizen-scientists who discovered a cluster of galaxies. Their research went on to be published in a peer-reviewed journal.

“For the majority of people, their number one reason for doing this work is that they want to contribute to real research,” Fortson said. “That, to me, is the light that will carry us through dark times. While we do have computers that can do some of this data crunching, computers cannot ask the question: ‘Huh, what the hell is that?’ We still need humans if we want to make serendipitous discoveries.”