The realization that we might be partly responsible for the recent spate of destructive weather is difficult to accept because it requires us to change the image of ourselves from innocent victim to guilty perpetrator. And, given the psychology of denial, we are inclined to avoid this sea-change of perspective. However, as climate science tracks the effects of the billions of tonnes of carbon dioxide we emit into the atmosphere from our burning of fossil fuels, its conclusions are forcing us to consider that our behaviour might be implicated in the extreme weather we are getting.

Weather, of course, is difficult to predict – this is why forecasts are often inaccurate. But climate is a much easier because general principles apply. Add heat and the weather becomes more active and extreme. Greater temperature differentials cause stronger convection activity and higher winds. When a 1.0°C rise in temperature increases the activity of the hydrological cycle by 7 percent, a modest warming translated into higher rates of evaporation and precipitation. (A disturbed hydrological cycle may explain why coastal BC is getting such a cold and wet spring this year – other places are getting our heat while we are getting their rain.) The climatic energy of warmer places always generates more dramatic weather.

Now apply these general principles of climate to the weather extremes that have recently traumatized Canada and the US:

• The Richelieu River in Quebec reached a record level in early May of 30.7 metres above normal. The unprecedented flooding was attributed to heavy rainfall combined with exceptional melt from the high snowfall in the Adirondack Mountains. The excessive rain and snowfall have been attributed to an increase in the activity of the hydrological cycle.
• Flooding has ravaged Manitoba, the worst in at least 300 years. The cause, as in Quebec, is excessive rainfall and the melting of unusually heavy snowpacks.
• Similarly, US states along the Mississippi River have been hit by record floods as unprecedented volumes of water make their way into the Gulf of Mexico.
• In a tragic irony, nearby Texas and the adjacent states of New Mexico and Oklahoma have been hit by record droughts and fires.
• “Unprecedented wildfires” were burning in 30,000 hectares of northern Alberta. Winds of 100 km/h swept one of the province’s 115 forest fires into the town of Slave Lake, burning nearly half the buildings in the settlement of 7,000 people. Similar conditions threatened Russia last year and are of concern again this year as some 400 forest fires burn uncontrolled through its dry forests. Last year, Australia ended a record drought with record floods. Pakistan got only an unprecedented flood. The Amazon, in four years, is in its second once-in-century drought.
• The tornado season in the US has been particularly destructive. April saw a record 600 twisters hit the South, causing widespread damage and a death toll of over 300. On a single day in May, a record of 226 tornados terrorized southern states. Then, on May 23, a horrendous tornado touched down in Joplin, Missouri, flattening a 1.6 km swath through the town, obliterating 2,000 buildings and killing 142 people – 90 more are missing. Two days later, 13 people were killed by a twister in Oklahoma. And the tornado season isn’t officially over until the end of June.

No one can be certain that global warming and the resulting climate change are implicated in these extreme weather events. Meteorologists are particularly careful to avoid the implication because the detailed causal connections are characteristically complex and uncertain. But indisputable global measurements show the biosphere is warming and the hydrological cycle is becoming more active. Extreme weather events are consistent with the computer models predicting the consequences of rising concentrations of greenhouse gases. The science is clear. It’s the specifics of weather that confuse us. We can’t be certain whether an individual weather event is extreme because of mere probability or because something more systemic and sinister is occurring.

But the simple physics of climate tell us that a gradual increase in global temperature will cause more frequent and sudden outbursts of extreme weather, extremes that we can erroneously attribute to the normally unusual. Such extremes that arrive in the guise of ordinary exceptions are particularly dangerous because each individual event can be rationalized, excused, overlooked and dismissed as if it were nothing portentous.

This has generally been our reaction to extreme weather events – we dismiss each one as a normal exception. Without the perspective of time, we fail to realize that once-in-a-century events are happening more frequently, or that melting ice is actually raising sea levels – BC government planners recently announced that all coastal structures with a design life to 2050 should allow for a 0.5 metre rise in sea level while those with a design life to 2100 should allow for a 1.0 metre rise.

Sea level rise, global warming and increasing storm intensity all came together in an “ecologically unprecedented” 1999 event in Canada’s Mackenzie Delta. High sea levels, the absence of Arctic sea ice to blanket waves, and a large surge from an intense storm all combined to send a flood of salt water 20 kilometres inland. This wide swath of the fresh-water Delta is still dead after 12 years. “It’s just another example of how recent climatic factors seem to be out of our normal range of variability,” said Professor John Smol of the Paleoecological Environment Assessment and Research Lab at Toronto’s Queen’s University. “We actually have evidence now that [global warming] has started happening and it isn’t just part of some natural variability” (Globe & Mail, May 17/11).

We all worry when weather’s variability becomes extreme. But we don’t want to accept that extreme weather events are actually linked to our greenhouse gas emissions, a reluctance that condemns us to be victims of our own doing – a sad irony that makes every weather disaster even more tragic.