The Intergovernmental Panel on Climate Change (IPCC) released a report Friday examining the risks posed by extreme weather events, which the panel says are becoming increasingly frequent around the world. We talked to one of the report's co-ordinating lead authors about what general trends he and his colleagues found and how these trends might impact Canada.

Gordon McBean is a professor of geography and political science at the University of Western Ontario in London, Ont., and the director of policy studies at the Institute for Catastrophic Loss Reduction. He is also chair of the Canadian Foundation for Climate and Atmospheric Studies and president-elect of the International Council for Science.

Extreme events

Definitions of what constitutes an extreme weather event vary, but for the purposes of the IPCC, the definition is based directly on measurements of things like temperature, wind velocity, precipitation levels and storm surge heights and where those measurements fall in a given region's weather distribution pattern.

Overturned vehicles are seen after a storm in downtown Genoa, Italy, on Nov. 5, 2011. Storms and torrential rains in northwestern Italy killed at least six people. The human and financial costs of such storms are often as severe as the weather. Alessandro Garofalo/Reuters

Generally, a weather event is considered extreme if it is as rare or rarer than the 10th or 90th percentile. For example, if the rainfall distribution for a given city is that only one in 10 rainfall events produce 90 mm or more of rain per day, then an extreme rainfall event would be any that produced 90 mm or more of rain.

Certain industries, however, have their own definitions.

"Other people in the disaster risk-reduction community would define an extreme event as one that, say, causes more than $1 million in damages," McBean said.

Global trends

Globally, 75 per cent of disasters are climate-related. That means they are caused by weather events such as floods, storms, droughts or snow avalanches — as opposed to earthquakes or volcanoes, which are generally not climate-related.

The frequency of climate-related disasters seems to be increasing, and the number of deaths they cause is also going up — although that could be in part because there are more people than in the past clustered in large urban conglomerations and along coastal zones and river deltas so when a disaster does strike, more are impacted.

McBean concedes that data on disasters for many regions of the world is weak but says that where it does exist, it shows a clear trend.

"Where we have good data on the observations of the climate, you can show that there is an increased frequency of high-precipitation events — even in areas where the amount of rainfall is … getting less per year for reasons of climate change," McBean said.

"There's more of these heavy rain events, [and] analysis done by scientists shows that that change is related directly to the greenhouse gas — increasing — concentrations. In other words, it's a part of the human-caused climate change."

Canadian weather changes

The number of very hot days in Canadian summers is increasing at the same time as the number of extremely cold winter days is decreasing, the IPCC scientists found.

"Canada, on average, is getting warmer. We're also seeing more heavy-precipitation events — mostly in the summertime — intense rainfall events, and these are having economic and social impacts on Canadians as individuals and on our society overall."

Economic impacts

The changing patterns of severe weather events have a multitude of environmental and socioeconomic impacts — from small power outages that bring our workday to a halt to raging wildfires that destroy entire communities. The insurance industry is one sector that has been raising the alarm about the financial impacts of changing weather patterns.

"The insurance companies are saying it used to be that the biggest concern they had for a homeowner insurance policy was a fire caused by a malfunction or something within the house, or a burglary," McBean said. "Their biggest costs now are wind/rain-induced events."

One such event was the August 2005 rainstorm in Toronto that washed out a major road and caused millions of dollars in damages.

"The water that came from that rain event — over ground, in through sewer systems, directly in through windows, in through the roofs of homes — resulted in insurance companies paying out over $500 million," McBean said. "That's the biggest loss in Ontario's history — one rain event in 2005."

And lest anyone think that is the insurance industry's problem, McBean warns that those costs are eventually passed on to all of us through higher premiums.

Projections

If the concentration of greenhouse gases in the atmosphere continues to increase as it has been doing, McBean says we can expect to see much less precipitation in the southern Prairies and southern interior of British Columbia. In the summertime, those regions will warm more than other parts of Canada, posing challenges for the local water supply.

A wildfire outside Lillooet, B.C, in August 2009 forced 2,000 residents from their homes and prompted firefighters to start controlled burns like this one in an attempt to reduce the amount of fuel from the fire. Summers in southern B.C. will only get hotter and drier, experts predict. Darryl Dyck/Canadian Press

"We're really concerned about increasing drought-like conditions in those areas," McBean said. "That whole trend is even more prevalent south of the border. So, the western part of the United States — the Californias, the Utahs, the Nevadas, up towards the border — is going to be increasingly drier in terms of a lot more heat, which means evaporating water, and a lot less precipitation, which means not much coming down. So, where's the water going to come from? That's a concern overall."

Canadians in the North can also expect to see further reduction of Arctic sea ice, McBean said.

What now?

McBean says that what Canadians should take away from the IPCC report is a realization that we need to work harder not just to reduce greenhouse gas emissions so that the kinds of trends identified in the report don't get worse but to begin adapting our infrastructure so that it is better able to withstand the impacts of severe weather events — by redesigning building codes, for example.

"Canadians should take this report, and they should individually and collectively, through their government, ... take action to reduce our vulnerability," McBean said.