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Those torrid days of summer - the extremes become the norm It appears that the rising global average temperatures, now well linked to greenhouse gas emissions, are raising the baseline around which our weather fluctuates by HENRY HENGEVELD Having lived in the middle of the Greater Toronto Area for more than 40 years, I thought I was relatively immune to its summer heat and bad air quality. After all, anyone that grew up mowing loose hay under a hot tin barn roof and tending the dusty grain bins during threshing time should be able to tolerate a bit of heat and smog. But this summer has been different. For the first time, I wished I had air conditioning in our house. Fans no longer seemed able to provide adequate relief for a good sleep on those steamy nights when temperatures stayed above 20°C and the high humidity left everything feeling clammy. On some of the hottest days, I also seemed to notice a shortness of breath. Am I just getting old, or has the summer really been that torrid and dirty? The data bear witness to the latter, although I can't deny that my age may be a factor as well. During this past June, maximum temperatures at the Toronto airport reached or exceeded 30°C for 14 days. In July, the number increased by 16. As I write this (in mid-August), another eight days have been added to the list, with promises of more to come. That's already a total of 39 days -- about one out of every two and more than three times the norm. Sixteen of those days (almost one out of every four) reached or exceeded 33°C, and on July 11, the mercury shot up to 35.5°C! There was little relief from the heat at night either, with minimum temperatures remaining above 20°C for one out of every three nights. Add humidity, and the days and nights became an exhausting succession of torrid discomfort. Pity the outdoor workers -- landscapers, road workers, roofers and, of course, farmers! Inevitably, the heat also contributed to a number of secondary effects. High temperatures increased evaporation of gasoline and other volatile chemicals and accelerated ozone-producing chemistry, both contributing to increased smog problems. By mid-August, the province had already issued a record setting 45 smog advisories. Energy consumption in the province, pushed up by over-worked air conditioners, reached record highs and, on several occasions, forced the utilities to impose rolling brownouts in order to avoid much greater power calamities. So why the all the heat? The direct cause was a persistent Bermuda high-pressure system that dominated the weather patterns of eastern and central North America for most of the summer. This system has kept the jet stream and related weather fronts well north of southern Ontario and created a persistent flow of moist, tropical air from the Gulf of Mexico. The same system, incidentally, also caused storms to track over Manitoba, causing record rainfalls in the region and a second consecutive year of disastrous crop planting conditions. Meteorologists have also noted that the Atlantic Ocean has been distinctly warmer this year, a factor undoubtedly contributing to the high-pressure conditions over eastern North America. The unusually high ocean temperatures have already contributed to a number of tropical storm records. The first such storm, dubbed Arlene, was the earliest on record. Each successive storm broke new timing records. With the worst part of the hurricane season yet to come and nine storms already registered by mid-August, the U.S. National Hurricane Center upped its estimate for the total number of tropical storms for the season by 50 per cent -- to between 18 and 21. They warned that 2005 could well become the worst Atlantic hurricane season on record. So what caused the unusual Atlantic Ocean conditions? Some will argue that the warm temperatures and persistent high pressures are simply part of the natural variability of the climate system. However, there is mounting evidence that there is more to it than that. Like the European heat wave of two years, the extreme conditions in eastern North America this summer are increasingly difficult to shrug off as just one of those events that happen from time to time. Rather, it appears that the rising global average temperatures, now well linked to greenhouse gas emissions, are raising the baseline around which our weather fluctuates. Gradually, the extreme year of 30 years ago is becoming more common, and current extremes are setting new records. A number of years ago, I participated in an analysis of how a rise in average temperatures across southern Canada, as predicted by Canadian climate models, might affect future temperature extremes in various Canadian cities. The results suggested that, for Toronto, the annual number of days with temperatures exceeding 30°C would double over historical norms by about 2030, and triple by 2055. That is, the extremes of 2005 will be the norm 50 years hence. Those numbers seemed almost unbelievable at the time. However, I am now convinced that it is already beginning to happen. According to a recent survey, so are 72 per cent of all Canadians. Welcome to the future! BF Henry Hengeveld is Emeritus Associate, Science Assessment and Integration Branch/ACSD/MSC, Environment Canada © copyright 2005 AgMedia Inc.. top back