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Victoria Slonosky, who is documenting climate change records in Canada, poses with a thermometer outside her home in St. Lambert, Que.Christinne Muschi/The Globe and Mail

The key to predicting future climate change may lie buried in some of Canada's oldest weather records, including the 1745 observations of a Montreal doctor and logbooks from William Parry's 1819 voyage to the Arctic. Now, a group of Canadian volunteers is racing to digitize those handwritten books before they fall apart.

They're part of a worldwide volunteer movement to hunt down old weather data, so that they can be used to test the newest climate-change models. In September, the Intergovernmental Panel on Climate Change will complete the first of three reports for its latest assessment of the world's climate. Climate models used in the final report, due the next year, will be judged in part on how well they can recreate past weather events.

"If these models can't capture the past, then we will have less certainty in using them to project into the future," said Rob Allan, manager of the International Atmospheric Circulation Reconstructions over the Earth initiative, at the Met Office, the United Kingdom's meteorological agency.

Historical records also reveal that debates about climate change are not unique to the 21st century. "We have been debating it in Canada for 300 years," said Victoria Slonosky, a climate scientist formerly with Environment Canada, who is spearheading the Canadian effort to catalogue old records.

While today's scientists focus on preventing climate change, their predecessors "seemed to be desperately hoping for climate change," Dr. Slonosky said. "A lot of them were from European descent and were puzzled because we are farther south than many places in Europe but the climate is harsher. … They were trying to figure out why."

Debate focused on whether cutting down trees and draining swamps would make Canada warmer.

In 1745, Jean-François Gaultier, the king's physician of New France, wrote: "The inhabitants of Canada claim that the winters are not as cold as they used to be, this they attribute to the large quantity of land which has cleared."

Others disagreed and began gathering weather data. That effort, Montreal judge John Samuel McCord wrote in 1826, "will be the first step towards the solution of that interesting question, whether our climate has changed since the first settlement of the country, and if so, in what degree?"

In more recent years, since May, 2010, 14 volunteers have spent their spare time typing 342,370 observations from as long ago as 1745 into computer spreadsheets. The Historical Canadian Climate Data ( volunteers include Web entrepreneurs, a member of the Canadian Forces, retirees, college professors, and even a descendent of the 19th-century notary and climate observer, Louis-Édouard Glackmeyer.

Dr. Slonosky stumbled upon old weather records when a train strike left her stranded in Paris. She found the phone number of the Paris Observatory in a guidebook. "I asked, 'Do you have old meteorological records?' They said, 'Yes, sure. They've been sitting here for 300 years!'" Dr. Slonosky said.

Back in Montreal, she found records dating back to the 18th century at McGill University Archives. Soon, she had gathered thousands of pages from archives across Canada. "All these things came to my attic," she said.

Later, when an illness made it difficult for Dr. Slonosky to type, she advertised for volunteers to help her transcribe the diaries.

Quebec and Atlantic Canada have the most complete historical weather records. "We have information on weather of the Montreal region, every day, several times a day going back to 1798," Dr. Slonosky said.

Early climatologists were dedicated observers. Alexander Spark, of Quebec City, recorded the temperature at 8 a.m. almost every day between 1798 and 1818 – alongside notes about "How to Remove Fleas," "How to Keep Butter," church gossip, money, politics and Nelson's victory at Trafalgar.

Such notes show that Canadian weather has been more variable than scientists once assumed, Dr. Slonosky said, with more hurricanes, snowstorms and floods in its history than had previously been known.

The efforts of current volunteers mirror the past they are preserving. The Historical Canadian Climate Data and the ACRE initiative are grassroots projects. "The history of meteorology is similar. Amateur observers were investing equipment and time trying to get government funding," Dr. Slonosky said.

Indeed, Halifax's George Young wrote in the Novascotian in 1827: "We have long regarded it as a subject of regret that so little attention has been hitherto paid to the collection of facts … for the climate of a country is one of the most useful and interesting enquiries that can be instituted."