Climate change could also affect transportation operations through impacts on mobility, efficiency, safety and demand.

Mobility and Operational Efficiency

All modes of transportation currently experience weather-related service disruptions. For example, up to one-quarter of all roadway delays⁽⁵³⁾ and an even higher proportion of air delays are weather related, according to American studies. It is virtually impossible to predict with any certainty the number of trip cancellations, diversions or delays that would occur under a changed climate, and what the social costs of these would be. There is a general sense, however, that fewer winter storms would benefit transport operators and the public at large.

In contrast, climate change is expected to have a negative effect on the efficiency of some freight operations, because of reduced payloads. The greatest concern is over shipping in the Great Lakes-St. Lawrence Seaway system. Virtually all scenarios of future climate change project reduced Great Lakes water levels and connecting channel flows, mainly because of increased evaporation resulting from higher temperatures (references 54 and 55; see also Water Resources chapter). Several studies on implications of reduced water levels for shipping activities in the Great Lakes^{(56, 57, 58)} have reached similar conclusions: that shipping costs for the principal commodities (iron ore, grain, coal and limestone) are likely to increase because of the need to make more trips to transport the same amount of cargo. Indeed, in recent years, lake vessels have frequently been forced into 'light loading' because of lower water levels. For example, in 2001, cargo volumes on the St. Lawrence Seaway were down markedly when compared to the previous five years, due in part to low water levels.⁽⁵⁹⁾ While the prospect of an extended ice-free navigation season is generally beneficial for Great Lakes shipping, it is unlikely to offset the losses associated with lower water levels.

Climate change may also result in reduced payloads for other modes of transportation, although these effects are likely to be relatively minor. Higher temperatures and especially more extreme hot days could reduce aircraft cargo-carrying capacities, owing to the fact that aircraft achieve greater lift when the air is colder (i.e., more dense). Heat is also a consideration for rail transport, since operators are sometimes forced to issue 'slow orders' due to heat kink dangers.⁽⁶⁰⁾ Also, milder winters or wetter springs could necessitate reduced loads on both private logging roads and public highways.

The impacts of warming on the fuel efficiency of motorized transport have also been considered,⁽⁶¹⁾ and are expected to lead to slight increases in fuel consumption for both road vehicles and aircraft.⁽²²⁾ For cars and trucks, this is due to an anticipated increase in air conditioner use, which would more than offset increased efficiencies resulting from reduced usage of snow tires and defrosting systems. For aircraft, increased fuel consumption is expected because warmer temperatures translate into lower engine efficiency.

Health and Safety

Weather contributes to a large number of transportation incidents in Canada each year, including approximately 10 train derailments and aircraft incidents, over 100 shipping accidents, and tens of thousands of road collisions.^{(2, 62, 63)} Some people have speculated that milder winter conditions may decrease the number of weather-related incidents, especially on roads, since it is well documented that collision rates increase during and after snowfall events. However, many snowfall-related collisions are relatively minor 'fender benders'. Human health and safety concerns relate principally to injury-producing incidents, which may tend to be more frequent under warmer weather conditions (see Box 2).

BOX 2: How does weather affect automobile accidents?⁽⁶⁴⁾

Ouimet et al.(64) investigated the correlation between weather variables, such as temperature, snow and rain, and automobile accidents in the Greater Montreal area between 1995 and 1998. Accident rates were found to peak in the summer months (June, July and August); fatal and severe accidents occurred almost twice as often as during the winter and early spring. As summer temperatures increased, accident rates also rose. Suggested explanations for this trend included the seasonal variations in traffic volume, and possibly also the effect of heat on human behaviour and alcohol consumption. In the winter months, adverse weather conditions increased the risk of minor traffic accidents in the study region. The effects of winter storms, snowfall and cold weather on accidents were especially pronounced on roads with higher speed limits, and roads in urban areas. Image courtesy of Natural Resources Canada Photo Database.

Recent research in several Canadian cities indicates that injury risks from transportation accidents are elevated by approximately 45% during precipitation events relative to normal seasonal conditions, but that increases are similar for snowfall and rainfall.⁽⁶³⁾ Therefore, any future shift that involves a decrease in snowfall events and an increase in rainfall, as suggested by most projections of future climate,⁽¹⁵⁾ is likely to have minimal impact on casualty rates. Where precipitation events become more frequent or more intense, however, injury risk could increase.

With respect to shipping, changes in ice conditions, water levels and severe weather could affect the demand for emergency response. For example, increased traffic in the Arctic due to reduced sea-ice cover would likely increase the occurrence of accidents.⁽⁴⁹⁾ Similarly, lower water levels in the Great Lakes-St. Lawrence Seaway system could increase the risk of ships being grounded, while higher sea levels and more severe weather could make marine shipping conditions more hazardous.

Indirect effects on human health may result from changes in transportation associated with climate change. For example, access to emergency health care may be affected by transportation disruptions, but there is little information on these types of issues. Relationships between air pollutants, including tailpipe emissions from cars, and air quality and human health are addressed in the Human Health and Well-Being chapter of this report.

Demand for Transportation

Economic and social factors are the main drivers of transportation demand. Because climate change is likely to affect local and regional economies, it will likely also have an indirect effect on transportation demand. While it is impossible to estimate the consequences of climate change for transportation demand with any certainty, it seems intuitive that climate change could affect the location and timing of demands for transportation of specific freight commodities, particularly those that are weather sensitive. For instance, should the spatial pattern of agricultural production change in response to an extended growing season or other climate-related factors (see Agriculture chapter), it is reasonable to expect some new demands for transportation to arise and some existing ones to wane. It is also reasonable to expect that climate change will impact tourism, regional growth, energy production and even immigration, with implications for geographic patterns of movement and demands on the various modes of transportation.

In addition to climate-triggered changes in demand, it is also important to consider transportation trends and forecasts⁽⁴⁾ and whether these are likely to amplify or reduce weather-related disruptions and costs. Most projections for North America forecast greater mobility in the decades ahead, both in an absolute sense and per capita, with road and air travel growing most rapidly.⁽⁴⁾ At present, both road and air travel have a number of weather sensitivities that are likely to continue into the future. These need to be addressed appropriately in climate change impacts and adaptation studies, as well as in decision making in the transportation sector.