When is a temperature record not really a temperature record?
Will Thursday’s temperature soar to a record level?
Well, the answer to that could depend on which statistics you use.
According to measurements taken at Pearson airport, Toronto’s heat record was set on Aug. 25, 1948 when it was 38.3 C.
Measurements at Pearson started in 1937. In 1936, downtown temperatures on July 9 were measured as high as 40.6 C, and the temperature reached 40 C three times between July 8 and 11.
But those measurements are less reliable and shouldn’t be considered the record high, said David Phillips, senior climatologist at Environment Canada.
“Downtown, it’s hard to get the numbers right,” he said. Using downtown measurements alongside those at Pearson is “like comparing apples with oranges,” he added.
The reliability issue comes in partly because of the urban heat island effect, which is mostly caused by heat-retaining materials such as asphalt and concrete. In addition, the downtown measurement site at the University of Toronto has changed places since 1936, whereas Pearson’s hasn’t, Phillips said.
The official record, then, is that 38.3 C day in August 1948.
Even if today’s mercury doesn’t crack 38.3 C, it could still be Toronto’s hottest-ever July day. That benchmark was set on July 7, 1988, when it reached 37.6 C.
-- Michael Woods, Staff Reporter