Technical summary of report findings from the CRBCPI assessment of the impact of climate change on climatic design data in Canada

Technical summary of report findings

How climatic design data for buildings and infrastructure was determined

Future climatic conditions depend, for the most part, on human-induced greenhouse gas (GHG) emissions. To investigate the effect of GHG emissions on climatic design parameters for this assessment, ECCC used well-recognized international and national climate change model results and reports, along with targeted regional modelling of the specific climatic design parameters in the National Building Code of Canada and the Canadian Highway Bridge Design Code, for over 660 locations. ECCC looked at various emissions scenarios and levels of global warming, from a low-emissions scenario roughly compatible with the Paris agreement, to a high-GHG-emissions, pessimistic scenario. ECCC then grouped information about changes in each climatic design parameter into levels of probability, from "exceptionally unlikely" to "virtually certain", according to their assessed confidence in the future projections.

The report findings illustrate that Canada's mean temperature is projected to continue to increase at roughly double the global mean rate, regardless of the emissions scenario. Looking at a low-emission scenario, the annual mean temperature in Canada will increase by 1.8 °C by mid-century from the baseline period. Under a high-emission scenario, where only limited emission reductions are realized, Canada's annual mean temperature would increase by more than 6 °C by the late 21st century.

These changes in Canada's temperature are accompanied by regional changes in precipitation, wind, snow, ice and extreme weather will have a significant impact on existing infrastructure. Detailed findings in each of these areas, along with potential impacts, were assessed by the NRC through the CRBCPI initiative, and include:

Temperature

Canada's climate has warmed and will continue to do so at about twice the rate of the global increase, regardless of emission scenario used, and even more in the North. A global temperature rise of 3.5 degrees translates to changes up to 8 degrees in Canada's north, and on average 4 to 6 degrees across Canada. The impacts are already being felt, as we are experiencing rising sea levels, changes to permafrost, and increases in heat waves, wildfires and flooding.

This also means that extreme warm temperatures have become hotter, while extreme cold temperatures have become less cold. The extreme July design temperature will increase by more than 4 °C on average across Canada, with highest increase of 6.6 °C at locations in the North and British Columbia. This affects both annual and seasonal mean temperatures across Canada with the greatest warming occurring in the winter. This will mean a longer growing season, warmer winters, and hotter summers. It means more air conditioning to address heat waves, more work to control moisture and humidity and less energy needed to heat our homes and indoor environments in the winter. All of these changes have an impact on the design and rehabilitation of buildings and infrastructure.

Precipitation

There is medium confidence that the annual mean precipitation has increased in Canada, with larger percentage increases in northern Canada. Both annual and winter precipitation amounts are projected to increase everywhere in Canada over the 21st century, with larger changes in northern Canada, while summer precipitation is projected to decrease over southern Canada. The shift in phases of precipitation from snow to rain with warming will lead to larger relative increases in rain across Canada. Increased precipitation means more moisture-related issues and mould in Canada's northern and Indigenous communities, and less rain in wildfire-prone areas in the summer.

Although evidence of historical changes in extreme precipitation is lacking for Canada, there is high confidence that daily extreme precipitation will increase with future warming. Extreme rain means more flooding, more moisture issues and mould, and more significant damage to Canada's buildings and infrastructure: roads, bridges, dams, sewage and storm water systems, as well as increased threat to human safety.

Wind pressure

While the gap in climate science makes predicting future wind loads difficult, the future changes in wind loads across Canada are thought to be relatively small and uncertain. However, projected changes can still have a significant effect on design, depending on location. In the simulations used to support the report, the wind load in Toronto, for example, is projected to increase by more than 13%. Understanding these changes will be critical to the future design and retrofit of skyscrapers and other buildings.

Snow and ice

The portion of the year with snow cover has decreased across most of Canada by 5% to 10% per decade since 1981, due to later snow onset and earlier spring melt. It is very likely that snow-cover duration will continue to decline due to increases in surface air temperature under all emissions scenarios. A reduction of 5% to 10% per decade in seasonal snow accumulation is projected over much of southern Canada. In the North, there will be smaller changes because increases in winter precipitation are expected to offset a shorter snow accumulation period.

Ice build-up, or ice accretion loads, are predicted to increase in several locations, particularly at latitudes higher than 50°N, with changes as high as 80% in some locations. This increase in load has significant implications for bridge design.

However, the permafrost temperature is expected to increase, and the projected increases in air temperature over land are virtually certain to result in continued permafrost warming and thawing over large areas by mid-century, with impacts on northern infrastructure and the role of northern terrestrial ecosystems in the carbon cycle.