Changes in Canada's Regions in a National and Global Context

Changes in climate have consequences for Canadians, their health, well-being, and livelihoods, as well as for natural ecosystems of Canada. Canada’s Changing Climate Report is the first report of the most recent national assessment process, Canada in a Changing Climate. This report assesses how Canada’s climate has changed, why, and what changes are projected for the future. It provides a physical science foundation for the other national assessment reports to be released in the coming years, which will assess recent knowledge on climate change impacts and progress in adaptation across regions and sectors in Canada (see Chapter 1, Section 1.1).

Given the large geographic expanse of Canada, historical changes in climate have varied across the country, and projected future changes will vary as well. Chapters 4, 5, 6, and 7 of this report provide assessments of changes in several aspects of physical climate for the country as a whole, including variations across the country. This chapter synthesizes information on historical climate trends and projected future climate changes for regions of Canada using information from these chapters. References to underlying sections in previous chapters are provided to link directly to the supporting evidence, along with detailed discussions of associated uncertainties, for the results presented here. This chapter begins, however, with an overview of global-scale climate change, which is the essential context for understanding changes in Canada.

There is overwhelming evidence that the Earth has warmed during the Industrial Era and that the main cause of this warming is human influence (see Chapter 2, Sections 2.2, 2.3, and 2.4). This evidence includes increases in near-surface and lower-atmosphere air temperature, sea surface temperature, and ocean heat content. Widespread warming is consistent with the observed increase in atmospheric water vapour and with declines in snow and ice. Global sea level has risen from the expansion of ocean waters caused by warming and from added water previously stored in land-based ice in glaciers and ice sheets. The observed warming and other climate changes cannot be explained by natural factors, either internal variations within the climate system or natural external factors such as changes in solar irradiance or volcanic eruptions. Only when human influences on climate are accounted for — changes in greenhouse gases, aerosols, and the land surface — can these observed changes in climate be explained. Of these human factors, the build-up of atmospheric greenhouse gases has been dominant, and carbon dioxide has been the dominant greenhouse gas emitted by human activity. Attribution studies provide quantitative assessments of the contribution of various climate drivers to observed warming over specified time periods. On the basis of such studies, it is extremely likely¹ that human influences, especially emissions of greenhouse gases, have been the dominant cause of the observed global warming since the mid-20th century.

Further warming is unavoidable under all plausible future emission scenarios, as some additional greenhouse gas emissions are inevitable. However, the extent to which future emissions of greenhouse gases, particularly carbon dioxide, grow or decline will largely determine how much future climate will change (see Chapter 3, Sections 3.2, 3.3, and 3.4). Canada and the world face very different futures, depending on the level and speed at which measures to reduce greenhouse gas emissions are implemented. If and when net emissions of carbon dioxide and other long-lived greenhouse gases reach zero, global average temperature will remain approximately constant for centuries at about the peak temperature attained. Other aspects of the climate system will continue to change even after emissions cease; for example, sea level will continue to rise (see Chapter 7, Section 7.5).

Warming globally and for Canada will be similar under all plausible emission pathways over the next two decades. However, efforts to reduce greenhouse gas emissions, beginning in the next two decades and continuing thereafter, will have an increasing impact on the amount of additional warming beyond this time frame. Available estimates indicate that, by the late 21st century, the global climate will warm by a further 1°C for a low emission scenario (RCP2.6) compared to a further 3.7°C for a business-as-usual high emission scenario (RCP8.5) (relative to the reference period of 1986–2005, with a 5%–95% range of about 1°C above and below the multi-model average; see Chapter 3, Sections 3.2 and 3.3).² These two scenarios reflect two very different global futures, as climate-related impacts and risks grow with increasing amounts of global warming. Only the low emission scenario (RCP2.6) is consistent with holding the increase in the global average temperature to below 2ᵒC above pre-industrial levels, in line with Article 2 of the Paris Agreement. This scenario requires global emissions to peak almost immediately, with rapid and deep reductions thereafter (see Chapter 3, Section 3.2).

Because air in the Earth’s atmosphere and water in the global oceans flow freely, Canada’s climate is intimately linked to the global climate. Thus, changes in Canada’s climate are a manifestation of changes in the global system, modulated by the effects of Canada’s mountains, coastlines, and other geographical features. For example, a robust feature of both observed and projected global-scale climate change is the amplification of warming at high northern latitudes (so-called Arctic amplification), which means Canada’s climate is expected to warm more than the global average (see Chapter 2, Section 2.2 and Chapter 3, Section 3.3). Canadian temperature has increased, and is projected to increase further, at almost double the rate of global mean temperature (see Chapter 2, Section 2.2 and Chapter 4, Section 4.2). Precipitation changes in Canada are also closely linked to global-scale changes, such as the overall intensification of the global water cycle, the increase in high-latitude precipitation, and the intensification of precipitation extremes that are projected as a result of greenhouse gas increases. Precipitation has increased in Canada since mid-century, particularly in northern parts of the country. Many other aspects of climate that are important to Canadians are also changing as a consequence of global-scale climate change. These changes include the extent and duration of snow and ice cover, permafrost temperatures, freshwater availability, fire weather, other extremes of weather and climate, sea level, and other properties of the oceans surrounding Canada (Chapters 4 to 7). Locations of places in Canada referred to in this chapter are shown in Figure 8.1.

There is no doubt that Canada’s climate has warmed. Temperature has increased in all regions of the country and in the surrounding oceans. Since 1948, Canada’s annual average surface air temperature over land has warmed by 1.7°C (best estimate), with higher temperature increases observed in the North, the Prairies, and northern British Columbia (see Chapter 4, Section 4.2.1). The greatest warming has occurred in winter. Human influence is likely the main cause of the observed increase in Canada’s temperature, as more than half of the observed warming in annual temperature in Canada can be attributed to human influence (Chapter 4, Section 4.2.1). Temperature extremes are also changing, consistent with the increase in mean temperature. Extreme warm temperatures have become hotter, while extreme cold temperatures have become less cold (see Chapter 4, Section 4.2.2). Overall, there is high confidence that most of the observed increase in the coldest and warmest daily temperatures in Canada (1948–2012) can be attributed to anthropogenic influence. Warming has also been demonstrated to have led to an increased risk of extreme fire weather in parts of western Canada (see Chapter 4, Section 4.3 and Box 4.2).

Observed changes in snow and ice features across Canada provide a coherent picture of a warming climate: fall and spring snow cover and summer sea ice extent are decreasing; glaciers are losing extent and mass; and permafrost is warming (see Chapter 5, Sections 5.2.1, 5.3.1, 5.4.1, and 5.6.1). Changes in relative (or local) sea level at locations along Canadian coastlines are driven primarily by the observed rise in average global sea level — a response to global-scale warming — and by vertical land motion (i.e., land uplift or subsidence). As a result, some coastal regions have experienced a larger relative sea-level rise compared to average global sea level, while others have experienced more modest increases or even decreases in relative sea level (see Chapter 7, Section 7.5).

Canada’s climate will warm further, with warming projected in all seasons. Projected warming for Canada as a whole is almost double that of the global average, regardless of the emission scenario (see Chapter 3, Section 3.3.3, and Chapter 4, Section 4.2.1.3). Country-wide annual average temperature projections for the late century (2081–2100) range from an increase of 1.8°C³ (1.1, 2.5) for a low emission scenario (RCP2.6) to 6.3°C (5.6, 7.7) for a high emission scenario (RCP8.5), compared to the base period 1986–2005.⁴ Further warming of extreme warm and cold temperatures is projected to be substantial (see Chapter 4, Section 4.2.2.3). In the future, higher temperatures will contribute to an increased risk of extreme fire weather across much of Canada. It is very likely that snow cover duration will decline to mid-century across Canada due to increases in temperature under all emission scenarios. Projections with a high emission scenario show continued snow loss after mid-century (high confidence) (see Chapter 5, Section 5.2.2). Oceans surrounding Canada are projected to continue to warm over the 21st century, in response to past and future emissions of greenhouse gases, with the size of the increase depending on the emission scenario. The warming in summer will be greatest in the ice-free areas of the Arctic and off southern Atlantic Canada, where subtropical water is projected to shift further north (medium confidence). Atlantic Canada will be the region of Canada’s oceans that will warm the most during winter (medium confidence) (see Chapter 7, Section 7.2.2).

Canada’s annual precipitation has increased in all regions since 1948, with relatively larger percentage increases in northern Canada and parts of Manitoba, Ontario, northern Quebec, and Atlantic Canada, although there is low confidence in observed regional precipitation trends. Mean precipitation has also increased in all seasons, except during winter in British Columbia and the western Prairies (see Chapter 4, Section 4.3.1). As a result of warming, snowfall has been reduced as a proportion of total precipitation in southern Canada. Seasonal snow accumulation has declined over the period of record (1981–2015) on a country-wide basis (medium confidence) (see Chapter 5, Section 5.2.1). The most significant observed changes in freshwater availability are in the seasonal distribution of streamflow in many snow-fed catchments: winter flows have become higher the timing of spring peak flows has become earlier, and there has been an overall reduction in summer flows (high confidence) (see Chapter 6, Sections 6.2.1, 6.2.2, and 6.2.3). However, many other indicators — annual streamflow magnitudes, surface and shallow groundwater water levels, soil moisture content and droughts — have, for the most part, been variable, with no clear increasing or decreasing trends (see Chapter 6, Sections 6.2.1, 6.3, 6.4, and 6.5). This variability corresponds to observed year-to-year and multi-year variations in precipitation, which are influenced by naturally occurring large-scale climate variability (see Chapter 2, Box 2.5).

In the future, annual and winter precipitation is projected to increase in all regions, with larger relative changes for the North. Summer precipitation shows relatively smaller changes and is projected to decrease in southern regions of Canada by the end of the century under a high emission scenario (see Chapter 4, Section 4.3.1). Daily extreme precipitation (that is, changes in extreme precipitation amounts accumulated over a day or less) is projected to increase; thus, there is potential for a higher incidence of rain-generated local flooding, including in urban areas (high confidence) (see Chapter 6, Section 6.2.4). Significant reductions in seasonal snow accumulation are projected through to mid-century for much of southern Canada due to warming surface temperatures, while only small changes are projected for northern Canada because winter temperatures will remain sufficiently cold despite overall warming (see Chapter 5, Section 5.2.2). In association with warmer temperatures, seasonal changes in streamflow are expected to continue, including shifts from more snowmelt-dominated regimes toward rainfall-dominated regimes. Shifts toward earlier snowmelt-related floods, including those associated with spring snowmelt, ice jams, and rain-on-snow events, are also anticipated. However, changes to the frequency and magnitude of future snowmelt-related floods are uncertain (see Chapter 6, Section 6.2.1, 6.2.3, and 6.2.4). Freshening of the ocean surface is projected in most Canadian waters over the rest of this century due to increases in precipitation and melting of land and sea ice. However, salinity is expected to increase in waters off the continental shelf south of Atlantic Canada as a result of a northward shift of subtropical water. The freshening in the upper layers of the ocean, along with warming, is expected to increase the “vertical stratification” (changes in density of ocean water at greater depths), which will affect the oceans’ ability to sequester greenhouse gases, dissolved oxygen levels, and marine ecosystems (see Chapter 7, Section 7.3.2).

The assessments of changes in climate provided in the key messages of Chapters 4 to 7 are associated with a level of confidence or a statement of likelihood, when possible. This assessment of uncertainty is based on the quantity, quality, and agreement of supporting evidence for changes assessed at the national scale. Uncertainty assessments are not always included in the regional summaries that follow, because uncertainties in regional-scale changes were not formally assessed within the previous chapters of this report. However, in general, for assessments at regional and local scales, the level of confidence in changes is lower and the uncertainty is larger, especially when assessing the magnitude (rather than the direction) of change (see Box 8.1).

To demonstrate regional differences and similarities, mean quantities for temperature and precipitation for six regions of Canada are provided below. For details about other temperature and precipitation quantities, including temperature and precipitation extremes for regions of Canada, readers are referred to the tables and figures in Chapter 4, Section 4.2.2, specifically Table 4.3, Figures 4.10, 4.11, 4.13 and 4.14 (temperature extremes and indices) and Section 4.3.2, specifically Table 4.6 (precipitation extremes). In all cases, values represent averages for the whole of the region and do not capture the significant variability between locations in every region. Information on climate trends and projected changes at the subregional and local scale are available from the Canadian Centre for Climate Services (https://www.canada.ca/en/environment-climate-change/services/climate-change/canadian-centre-climate-services/about.html). For further information on regional changes to sea level and other coastal issues, readers are referred to the recent report on Canada’s Marine Coasts in a Changing Climate (https://www.nrcan.gc.ca/environment/resources/publications/impacts-adaptation/reports/assessments/2016/18388; see Chapter 1, Section 1.1).

Canada’s Changing Climate Report describes a Canada that has warmed and will warm further. Historical warming has led to changes in rain and snow, rivers and lakes, ice, and coastal zones, and these changes are challenging our sense of what a “normal” climate is. The world’s climate, including Canada’s climate, is changing because of human emissions of greenhouse gases, particularly carbon dioxide (see Chapter 2, Section 2.3, and Chapter 4, Section 4.2.1). Beyond the next few decades, the largest uncertainty about the magnitude of future climate change is rooted in uncertainty about human behaviour, that is, whether the world will follow a pathway of low, medium, or high emissions (see Chapter 3, Sections 3.2 and 3.3). Until climate is stabilized, there will not be a new “normal” climate.

Attribution studies have shown that anthropogenic climate change has influenced some recent extreme events, as well as long-term regional-scale trends (Chapters 4, 5, 6, and 7). In the future, anthropogenic climate change will continue to affect aspects of climate important for agriculture, forestry, engineering, urban planning, public health, and water management, and the preparation of guidance and standards. The challenge for users of climate information is to determine how best to incorporate climate change information into the various methods and tools used for assessment and planning across these sectors. The information brought together in this report is intended to guide this process, informing the preparation of new standards, the assessment and management of climate-related risks, and the design and implementation of climate adaptation plans.

The Canada in a Changing Climate series of reports, led by Natural Resources Canada, will assess available knowledge on climate change impacts and adaptation across regions and sectors. Canada’s Changing Climate Report is the first publication of this series, and it has established a foundation of knowledge about how Canada’s climate is changing and why, as context for assessing impacts and adaptation responses.