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Has Canada’s climate already changed?

Digging out in Toronto- 1961 (Courtesy: City of Toronto Archives)

Digging out in Toronto- 1961 (Courtesy: City of Toronto Archives)


Rob Davis
Meteorologist

Wednesday, August 14, 2013, 10:36 AM -

Canada sure was a different place 50 years ago. The country’s centennial was approaching, a new national flag was in the works, and one-dollar bills were still in circulation.

But how about the weather? Does our memory serve us well? Are those tales of harsher weather true?

Climate change is a hot topic (pun intended). Just uttering the words “climate change” or “global warming” are almost sure to induce strong opinions, and possibly even a political debate. There are many forecasts of the world’s future climate, with the world’s top climate scientists working with imperfect datasets and many assumptions, but often pointing towards a warmer climate in our future.

But this article has a different focus. The question posed here looks only into the past, and stays in our own backyard. The question: Has Canada’s climate already changed?

More specifically, have Canada’s major cities seen a change in their weather patterns since the 1960s? Let’s narrow our scope down to just four of Canada’s largest cities: Toronto, Montreal, Vancouver & Calgary.

TORONTO

It’s 50 years ago in the City of Toronto. The Don Valley Parkway has just opened, the CN Tower is a decade away from being built, and The Maple Leafs are still winning Stanley Cups.

Pearson Airport would not be known as such for another two decades. In fact, Lester B. Pearson had just become Prime Minister in 1963. First known as Malton Airport, it was renamed to Toronto International Airport in 1960, then finally to Pearson Airport in 1984.

Continuous weather observations have been kept at the airport since 1937. This dataset sheds some light on the city’s changing climate for the past three-quarters of a century.

This graph shows how temperatures are noticeably warmer than they used to be, with the 10 hottest years being in the last fifteen years on record. 2012 was actually the warmest year in the city’s record.

In the 1960s, the average temperature was close to 7 or 8°C. Nowadays, it’s more like 9°C.

But let’s dig deeper. This number is an average of every temperature year-round, day and night. Maybe different times of day, or times of year, hold the bulk of this new increase in temperature.

It’s subtle, but it’s clearly there: Day temperatures are arguably similar to, or slightly above, daytime temperatures seen in the mid-20th century. But night temperatures are clearly warmer than they used to be.

A look into data from the University of Toronto – where records go back to 1840 – show this pattern even more. Over 80% of daily cold records from the UofT weather station that still stand today were set in the 1800s.

As of the writing of this article, Toronto’s Pearson Airport had not broken a daily cold record in almost 8 years – almost 3000 days in a row. The odds of this occurring due to pure chance are astronomical (less than 1 in a trillion).

MONTREAL

50 years ago, Montreal’s skyline was in the midst of an overhaul, with many of the city’s tallest buildings being built at the time. The city was also busy preparing to host two major international events in the years to come: Expo 67, followed by the 1976 Summer Olympics.

Montreal-Trudeau Airport, then known as Dorval International Airport, was built in 1941. Weather observations from the airport began in the same year.

Montreal’s temperature history is very similar to that of Toronto. Temperatures have clearly warmed in recent decades, with average annual temperatures only recently beginning to consistently surpass those seen in the 1940s & 1950s.

So does that mean the weather seen today in Eastern Canada is similar to what it was like in the mid-20th century? Well, no. We’ve already determined that nighttime temperatures have increased more than daytime temperatures. But what about precipitation? More specifically, what about snowfall?

Montreal has the largest snow removal budget in the world, and anyone who has lived in Montreal for even one winter can quickly appreciate why. Last winter, Montreal broke its record for the largest one-day snowfall in the city’s recorded history: 45cm of snow in just one day.

However, when taking a look at the data, annual snowfall amounts have actually been dropping.

In 50 years, annual snowfall amounts have dropped about 15%. Clearly not everything is as it used to be, and this may be a sign of the winter season taking on more of the overall warming in recent decades.

VANCOUVER

In 1963, metropolitan Vancouver was approaching one million residents, with the city’s suburbs rapidly expanding. The area was still cleaning up after the remnants of Typhoon Frieda (known as the “Columbus Day Storm” in the United States), which had crossed the Pacific Ocean and struck the North American west coast, including Vancouver. The storm killed 6 people in British Columbia.

Construction of Vancouver International Airport began in 1930, with weather observations commencing in 1937. Due to the airport’s proximity to the Strait of Georgia, temperatures are more moderated than areas further inland. It’s interesting to see the climate patterns that emerge from this west coast weather station.

Even with its proximity to a large body of water, the temperature increase is quite obvious. Even with warmer temperatures recorded in the 1960s, temperatures are slightly higher than they were 50 years ago. Vancouver recently saw its hottest two days ever recorded in July 2009. The following winter, a lack of snow threatened the 2010 Winter Olympics.

Telltale information lies in the rainfall numbers. Annual rainfall amounts have increased by over 10% since the 1960s, and extreme daily rainfall events have arguably become more frequent.

CALGARY

50 years ago, Calgary was one of the fastest growing cities in Canada. With over 250,000 people, the oil industry had caused the city’s population to double within a decade. The Calgary Tower was soon to be built, and the city was becoming a thriving metropolis.

Calgary International Airport, now tied with Montreal-Trudeau for Canada’s 3rd busiest airport, behind Toronto Pearson and Vancouver International, started out as a grass airstrip in 1914. Weather observations at the airport’s location predate the airport itself, with records going back to 1881.

Calgary’s temperature record is much more sporadic, but a linear regression line shows a possible slight warming trend over the time period. Not very reliable information on its own, but is every time of year as noisy as this?

It turns out -- and any Calgarian can attest to this -- winter is by far the most varying season, year-to-year. In the past, two consecutive winters can be as much as 10°C different in overall temperature.

However, within the highly-varying temperatures of a Calgarian winter, there does appear to be a warming pattern. Winters just aren’t as cold as they used to be. Before 1980, Calgary used to have three winters per decade of -10°C on average or lower. Since 1980, the average is less than 1 per decade.

Calgary’s recent flooding event has also sparked talks of a changing climate in the city.

WHY IS IT DIFFERENT?

Canada’s major cities have seen changes to their overall weather patterns. Nighttime temperatures are noticeably warmer, snowfall amounts are on the decrease, and winters are warmer.

But is this due to greenhouse gases? Or is this just a byproduct of living in a growing metropolitan area?

The likely answer is a combination of both, and different for each categorical type of change. For example, warming nights is a well-known by product of urban development. Urban settlements are made of material that is more likely to retain heat throughout the night, thus keeping temperatures warmer than they otherwise would be at night. The phenomenon is known as the urban heat island effect.

The urban heat island effect tends to break down during stormy events, and winds increase. So what explains Montreal’s lowering annual snowfall amounts? Changing weather patterns may be the cause of this trend, but this is not certain.

Is this also the possible explanation for warmer Calgarian winters? The answer likely lies in the Canadian Arctic, where climate change is currently the most obvious. In short, cold arctic outbreaks may not be as frequent nor as intense as they used to be.

Whatever the root cause of these changes in the weather of our major Canadian cities, one thing is clear: Canada’s weather has changed from “back in the day”.

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