• Extreme weather and climate change
    Summer 2013 Already Experiencing Significant Extreme Weather
    Weather on "Steroids"
Thursday, 18 July 2013 19:33

Extreme weather and climate change

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It's mid-July, and summer has already produced a number of very significant and newsworthy weather events. But can we blame climate change? Yes, but it isn't as simple as saying that climate change caused any single event. Consider the following:

On June 20th, continued heavy rains in southern Alberta overwhelmed many streams and rivers emanating from the Rocky Mountain foothills, causing widespread flooding across the entire region, causing road and bridge washouts and forcing evacuations in towns upriver from the city of Calgary such as Turner Valley, High River, Cochrane, and Okotoks. By the evening of June 20th, more than twenty low-lying neighbourhoods in the City of Calgary itself were under mandatory evacuation orders as both the Bow and Elbow Rivers crested their banks, flowing at three times the peak levels of the 2005 floods that was among the costliest extreme weather events in the Alberta`s history. The rivers flooded streets, transitways, offices, stores, and homes. Power outages were widespread, the entire downtown closed off, and travel not recommended across much of the city. In total, four people died as a direct result of the floods, and – while still very preliminary – costs are expected to be in the $3-5 billion range.

Just two and a half weeks later, the City of Toronto was hit by a severe thunderstorm that, in just a couple of hours, dumped 126mm, or double the monthly average for July, on the city. Amazingly, that was more than was recorded during the record-breaking and urban-environment-shaping Hurricane Hazel in 1954 that destroyed hundreds of homes and killed 81 people. This time, hundreds of thousands of people lost power (many for more than 24 hours), many more were stranded on flooded highways and subway stations, and 1400 people had to be rescued from a GO commuter train that flooded out in the Don Valley. The total costs of this storm are expected to exceed $600 million.

This week of July 15th, southern Ontario, Quebec, and the northeast United States have been experiencing what is becoming commonplace in summers: multiple days where temperatures rise to the mid-30s, with humidex readings well into the +40s. In the United Kingdom, the past nine days have produced the country`s first prolonged heatwave in nearly a decade, and estimates have placed the number of premature deaths at more than 600 as a result.

Of course, these types of extreme events have existed forever, and it would be incorrect to place all of the blame of these events on changing climates. But climate change does have a role to play in causing this extreme weather and will continue to exert its influence in the future, meaning increasing numbers of more extreme weather events. The challenge is often explaining the difference between "normal" extreme weather and "climate change enhanced" extreme weather.

Luckily, Dr. Jerry Meehl, Senior Scientist at the National Center for Atmospheric Research in Colorado has given climate change communicators an easy-to-understand analogy that helps illustrate what climate change is doing to our weather (see video below).

In short, Dr. Meehl likens climate change's impact on extreme weather like what is listed above to steroids' impact on players hitting home runs in Major League Baseball. These players would have been able to hit home runs before, but after steroids, many more homeruns were being hit and they were often being hit farther as the players' background base states were changed. Because of past home run-hitting abilities, you couldn't say any particular home run was the result of steroids, but the overall numbers went up after steroids were being used. Climate change is having a similar "steroid effect" on extreme weather: we can't say that any single extreme event is specifically the result of climate change, but the frequency and intensity of extreme events is certainly rising as the background base state of our global climatic system is changing. 

These are significant events that impact cities, towns, and regions in many ways: by putting residents in danger, by dedicating staff time and resources to emergency management and cleanup, by disrupting economies, and by forcing limited funds to be spent. With more of them coming as the climate changes at a rapid pace, it behooves local governments to look at what impacts they might be expecting, and decide how best to prepare and adapt to them so their towns and cities remain livable, resilient places. Visit ICLEI's Building Adaptive & Resilient Communities page for how we can help.