Kiyoshi Miyasaki, a priest, points out some of the records on lake ice and the omiwatari, an ice ridge. His data sheet summarizing the records are on the table. Image credit:  John J. Magnuson 

Climate change may seem like a fairly new topic for scientific investigation—going back a few decades, perhaps—but a new study published in Nature Scientific Reports shows that people have been tracking changes in climate for much longer than previously thought. The study, which examined records from far northern Europe and from Japan stretching back to the 17th and 15th centuries, respectively, found that those early records—like those collected more recently—point to the same troubling conclusion: The world has been getting warmer ever since the Industrial Revolution.

In 1442, Shinto priests in the Japanese Alps started keeping track of the date on which a nearby lake froze. And in 1693, merchants in northern Finland began to track the date on which ice would break up on a local river. Taken together, these are the oldest inland water-and-ice records known.

“These are direct observations of climate, and they’re very consistent with each other,” biologist Sapna Sharma of York University in Toronto tells mental_floss.

The data from both locations can be plotted as approximately straight lines, showing only a very slow change in the freeze-date in Japan (which moved gradually earlier), and in the melting date from Finland (which moved gradually later), until the 19th century—at which point “the slope of the line changes significantly,” indicating a rise in temperatures, Sharma says.

The international team of researchers was led by Sharma and by John J. Magnuson, a limnologist (an expert on inland waters) at the University of Wisconsin in Madison. 

The Japanese data was collected by priests at Lake Suwa as part of a ceremony honoring two gods said to dwell on opposite sides of the lake. According to legend, the male god, Takeminakata, would cross the frozen waters to visit a female god, Yasakatome, at her shrine on the other side of the lake. In Finland, the freezing of Torne River was important to traders, merchants, and travelers. Record-keeping continued in both locations right up to the present, with few interruptions, Sharma says: “The Scandinavia data only has six missing years—when the Russians invaded Finland, and the record keeper had to flee.”

In Japan, the upward trend in temperature begins in the 1810s, while in Finland it begins around 1867—reflecting the later start of industrial activity in far northern Europe. “We looked at climate records, and diaries that people had kept describing the climate, and it seems to be consistent with when things started to warm up in both of those regions,” Sharma says.

In Japan, for more than 200 years, the freeze-date moved by only a tiny amount from year to year—less than one-fifth of a day per decade, on average. After the onset of industrialization, however, that rate climbs to 4.6 days per decade. The Finnish data show a comparable change.

The data are consistent with other studies of long-term climate change based on theoretical models as well as “paleo” studies (what scientists have been able to infer from sediment, ice cores, and tree rings) and from modern record keeping of ocean and air temperatures and atmospheric carbon dioxide levels, Sharma says.

The findings “provide a nice source of confirmation for other lines of evidence,” Michael Mann, an atmospheric scientist at Penn State University, who was not involved with the study, tells mental_floss. Attempts to model changes in Earth’s climate over time rely on extrapolations of modern data, so having these early records can help scientists refine their mathematical models, Mann says. This, in turn, can help us predict what may lie ahead. “The better we are able to reproduce documented past changes in climate, the more confidence we have in our projections of future, human-caused climate change using the same climate models,” he says.