Montreal has lost a third of its snow since 1863

Montreal winters got about a third less snow at the turn of the millennium than in the mid-19th century, according to an analysis of decades of meteorological data compiled by McGill University.

“We realize that we're more obsessed with snow today than we used to be, even though there used to be more snow, precisely because it was usual for there to be more,” said Frédéric Fabry, head of McGill's Bieler School of the Environment.

“On the other hand, flooding is just as catastrophic.”

The McGill Meteorological Observatory is the oldest in Quebec and the second oldest in Canada. Founded in 1863, all the data recorded there until 1992 was done by hand, often several times a day, in large notebooks resembling accounting books.

The SAM (weather archive rescue) project was set up in 2018, led by McGill's Victoria Slonosky, to make use of the wealth of data.

The aim of the project is to digitize information to facilitate study, analysis and sharing. The task, however, is colossal: it has been calculated that it would take between 45,000 and 50,000 hours of work to transcribe everything — the equivalent of a lifetime's work.

“An American colleague pointed out to me that it's like asking all the spectators at a football match to work for an hour,” said Fabry.

So those in charge of the SAM project decided to turn to the citizen science model, calling on volunteers to tackle the job. So far, their collaboration has made it possible to transcribe around a quarter of the handwritten data.

The first step was to digitize the microfilms that had already been made of all this data, so they could be made available online.

“Since people can't come to the books, the books had to go to the people,” Fabry said.

However, the images are irregular, he added, and there was no way of automating the process.

“We did try asking computers to do the job,” said Fabry, but the results were “disastrous.” Machines are in fact incapable, at least for the moment, of deciphering each person's calligraphy, or of interpreting the various shortcuts (such as symbols indicating repetition) used by humans.

Before 1975, for example, barometric pressure was recorded in inches of mercury, due to the imperial system, he said.

“A regular pressure measurement is 30,234 inches of mercury,” said Fabry. “If the next measurement is the same, (the person will) rewrite only 234. But if you feed that directly into a machine, imagine the disaster...”

The goal is to be able to compare past and present with the same standards.

“What has changed? What's more frequent, what's less frequent? We were interested in knowing the details of the climate of the past, so we could shed more light on the present climate and how it is changing, and how significant these changes are,” said Fabry.

Climate change

The project gains more relevance in the context of climate change, the effects of which are increasingly being felt, Fabry said.

“To know how the climate is changing, you have to know how it was before,” he said. “And with detailed information, we can see, for example, rapid accumulations (of water) over two hours like we see in thunderstorms now, did we see that before?”

The SAM project, added Fabry, illustrates how our vulnerabilities to weather have evolved over time, as our society changes along with the climate.

For example, at one time, we recorded what we called “gliding conditions,” since travel was by horse-drawn sleigh. We were also interested in when the St. Lawrence River was frozen enough to be crossed, since Montreal was an island before the Victoria Bridge was built.

But over time, concerns changed, Fabry noted.

“Before electrification, freezing rain didn't bother anyone,” he said. “But today, society is so dependent on electricity that everything stops (in the event of a blackout).”

This report was first published in French by The Canadian Press Oct. 19, 2024