A future of more weather and climate extremes

Blog - March 4, 2014 - By John Stone

Alberta experienced severe flooding in 2013. Photo: Julia Kilpatrick, Pembina Institute

 The Alberta floods of this past summer were the number-one Canadian weather story of 2013. More recently, California governor Jerry Brown declared a state of emergency as a result of an extended drought that is threatening crucial North American food production. And this winter, the United Kingdom has been experiencing extreme flooding and devastating storms of a scale not seen for centuries.

Any one of these extreme events could be dismissed as usual weather variability. Although we must be prudent not to attribute every extreme — or indeed any particular one — to climate change, taken together these events may indicate a new normal.

The global climate system

The Intergovernmental Panel on Climate Change has concluded that climate change is unambiguous and that human influence is extremely likely to be the dominant cause. Can we then attribute these extreme events to human-induced climate change? We have not yet reached a full scientific verdict, although the evidence is quite convincing for some extremes such as heat waves.

As mean air temperature increases, there is a change in the probability distribution of the observed temperatures and we see more extremes in the wings. Roughly speaking, extreme temperatures have gone up by at least two degrees, which is more than twice the increase in global average temperatures.

We are currently observing twice as many record hot days as record cold days. Heat waves not only threaten the weak and aged, they also threaten crop production. We saw this in 2010 when Russia stopped its grain exports following a disastrous harvest caused by a severe heat wave.

Climate change is not simply a smooth increase in global temperatures. It is evident in changes in precipitation, the decline in Arctic sea ice and the increase in sea levels. It is also characterized by changes in extreme weather and climate events. As the Earth’s atmosphere and oceans grow warmer, there is more energy in the climate system and it becomes more volatile. As a consequence, there will be an increase in the frequency and severity of extreme events.

Furthermore, the atmosphere can carry more water vapour as air temperature rises, making rains or snowfalls more intense. The result is the kind of flooding we saw in Toronto last summer. In short, climate change has loaded the dice such that the chance of an extreme event is greater.

The costs of extreme weather

We may experience climate change most dramatically through the changes in extreme events. Although these events are of a relatively short duration, the damage they inflict can take a much longer time to repair. The state of New Orleans illustrates this: the city still has not recovered from Hurricane Katrina nearly a decade ago. When several extreme events occur in short succession, there is often not enough time to respond to the first before the next one occurs.

According to data from the insurance industry, the frequency of weather disasters has tripled since the 1960s. Insured losses have risen tenfold and in Canada water damage now exceeds fire damage.

One must be careful not to attribute all of this damage to climate change alone, for there are other factors to consider. For example, there has been a significant increase in property values in flood plains and coastal areas. Nevertheless, sensible prudence suggests that we should prepare for more extremes.

Cold weather and a changing climate

The brutal and extended cold weather that has affected much of Canada this winter has caused some to question the notion of global warming — although Alaska and other parts of the world have been experiencing above-normal temperatures. This extreme cold can be explained in terms of a series of connected climate changes. These changes illustrate the global nature of the threat and expose our inadequacy in imagining what the future impacts may be.

Rebuilding after the 2013 flood in CanmoreThe story starts with extreme and persistent rainfall over the tropical West Pacific, which has lead to warmer-than-normal sea surface temperatures as the oceans take up more heat from the climate system. This, incidentally, may be linked to the “hiatus” in surface air temperatures observed over the past decade.

The warmer ocean has dramatically affected the jet stream’s path over North America and produced a polar vortex that dipped to much lower latitudes, bringing cold Arctic air to Canada and much of the United States. This polar vortex spawned a series of deep low-pressure systems that crossed the Atlantic, causing devastating storms to hit the western coasts of the U.K. This is an awesome illustration of the concept of “one atmosphere.”

This story illustrates the kinds of surprises that the climate may have in store for us. There are likely to be more surprises in the future, and many of them will not be welcome ones. Weather and climate extremes are a normal part of the natural variability of the climate. However, the clustering and persistence of recent extremes around the world is a wake-up call to the power of nature and the threat of climate change. We have been issued a warning.

Tags:  Climate Policy.

John Stone

John Stone is an adjunct research professor in the Department of Geography and Environmental Studies at Carleton University, and is widely regarded as an expert on climate change and international affairs. He serves as Secretary of the Pembina Institute's Board of Directors.


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