Canada's Changing Climate Report
Government of Canada, 2019
Canada’s Changing Climate Report (CCCR) is a document published in 2019 by the Federal Government that describes past changes and projects future trends in Canada’s climate. It represents a collaboration between scientists at Environment and Climate Change Canada, Fisheries and Oceans Canada, Natural Resources Canada, as well as experts from various universities. This report focuses solely on physical climate science and is the first major product of a broader National Assessment entitled Canada in a Changing Climate: Advancing our Knowledge for Action. Building on the climate science of this initial report, subsequent documents will examine how climate change is affecting Canadians, including impacts to our communities, health and wellbeing, and economy, while also exploring opportunities for adaptation.
Prior to honing in on specifically Canadian content, CCCR provides a general overview of global changes. The take home messages from this section should not come as a surprise to most people: Yes, the earth’s climate is changing, and yes, human activities (particularly those involving greenhouse gas emissions) are the main cause of the planet’s observed warming since the mid 1900’s (via the mechanism of the greenhouse effect). These findings are well established using a variety of measurements across all of the interacting components of the climate system: The atmosphere (gases), hydrosphere (water), cryosphere (frozen elements), biosphere (all life on earth), and the surface of land.
Computer models are an important tool used by climate scientists to project future changes, and CCCR dedicates a chapter to describing the key features and possible limitations of various climate models. Since it’s impossible to know exactly how much carbon humans will continue to emit, the results of climate change models are dependent upon a range of scenarios in which future human activities are a decisive variable. According to most estimates, the earth will warm by a similar amount over the next 20 (or so) years across all emissions pathways. However, the devastating effects of a ‘high emissions’ scenario would be very evident by the end of the 21st century as the earth’s temperature will increase by an additional 3.7°C (relative to a 1986–2005 reference period). To stay in line with the Paris Agreements’ target of limiting the global temperature increase to 2.0°C (above pre-industrial levels), a ‘low emissions’ scenario would require dramatic societal changes involving a near immediate peak and a rapid decline thereafter in global carbon emissions. Climate models also indicate that once carbon has been released into the atmosphere, the resulting increase in global temperature is essentially impossible to reverse. CCCR further discusses the use of ‘downscaling methods’ to model more localized, although more uncertain, changes for a specific region (as opposed to the entire earth system).
Moving on, information concerning temperature and precipitation across Canada is condensed into one chapter of CCCR. Between the years of 1948–2016 it is reported that Canada’s temperature increased at double the average rate of all countries, with temperatures in Canada’s North rising at three times this mean global rate. As warming trends continue, Canada is projected to experience milder winters and a prolonged agricultural growing season. However, more days of extreme heat are also in the cards, posing a serious risk to human health and increasing the potential for wildfires. Levels of precipitation are expected to increase across Canada throughout the 21st century; and, as with temperature, Canada’s Northern regions will experience these changes more drastically. Canadians can also expect to see more rain instead of snow during the ‘shoulder seasons’ of spring and fall. With these trends in mind, it’s logical to wonder whether climate change is to ‘blame’ for recent extreme events that have severely impacted Canadians, such as the 2016 wildfires in Fort McMurray and the 2013 floods in Alberta. CCCR notes that causal relationships are difficult to pinpoint, but we can nevertheless assume that human-caused climate change made these extreme events more likely to occur.
Among other reputations, Canada is known for its frigid winters and frozen landscapes. In the context of climate change, CCCR examines how increasing levels of precipitation and rising temperatures are affecting snow, ice, and permafrost across Canada. It’s clear that snow cover (in all regions), as well as sea ice and alpine glaciers (in the Arctic), are in decline. Perennial sea ice (ice that typically doesn’t melt in the summer) is vanishing in place of thinner seasonal ice. Permafrost (ground that is frozen year round) has also increased in temperature over the past 3-4 decades and has even melted in certain regions, forming depressions in the land called ‘thermokarsts’. These troubling trends are projected to continue across all emissions scenarios, but actions taken now to substantially reduce carbon emissions can help mitigate the severity of future impacts. Again, CCCR focuses solely on physical science, but future reports will unpack the significance of these dramatic and interconnected changes for Indigenous communities and wildlife in the Canadian Arctic, as well as coastal communities who will face rising sea levels accelerated by the rapid melting of Arctic ice formations.
On a seasonal basis, melting snow affects the volume of surface runoff (streamflow) and surface water (lakes and wetlands), as well as associated soil moisture and groundwater levels. In Canada, warming temperatures have caused snow to melt earlier in the year, and streamflow is expected to continue shifting to an earlier springtime onset. Changes in the timing of snowmelt, and the compound effect of rain falling on snow, could also lead to a heightened risk of unseasonable flooding. Rising temperatures can further reduce freshwater availability in ‘continental interior’ Canadian communities (away from the coasts) due to increasing levels of evapotranspiration (water evaporating into the atmosphere). The possibility of worsening drought conditions was also mentioned in CCCR, primarily with respect to the southern parts of the Canadian prairies and the interior region of British Columbia.
Turning now to the oceans surrounding Canada, CCCR projects that the salinity of surface water will decrease in most areas due to increasing levels of precipitation and ice melt (which, in effect, dilute the salty water). Coupled with warming temperatures, this ‘freshening’ of salt water can decrease the upper ocean’s density and affect how nutrients and gases are distributed which, in turn, impacts marine ecosystems. Decreased concentrations of subsurface oxygen is one serious consequence of this phenomenon, as is a decrease in available nutrients (particularly observed in the North Pacific Ocean). Moreover, sea water (especially in the Arctic Ocean) will continue to experience acidification as a result of elevated atmospheric carbon dioxide linked to human activities. Rising sea levels are another well-documented aspect of climate change, and parts of Canada’s Atlantic coast will see a relative change in sea level that surpasses the global average. Dangers posed to Canadian communities by elevated water levels and coastal erosion are fairly region-specific, and adaptation efforts to minimize risks should be informed by local projections of change whenever possible.
The final chapter of CCCR summarizes past and projected changes in different regions across Canada, namely Northern Canada and Southern Canada (sub-divided into Quebec, Ontario, the Prairies, British Columbia, and the Atlantic region). While the key information in this chapter was already presented elsewhere in the report, grouping together region-specific results is pertinent due to Canada’s large geographic area and numerous distinct climates. This also provides an intuitive way for policymakers, educators, and any interested readers to learn more about climate science as it pertains to their home region in Canada.
Canada’s Changing Climate Report is a landmark document that paints a picture of how climate change has, and will continue to affect, Canada, while also contextualizing our place within the interconnected global climate system. The observation that Canada is warming at roughly double the global rate is certainly alarming and garnered high profile media attention. CCCR, serving as a foundational source of Canadian physical climate science information, can facilitate the implementation of more informed climate targets, monitoring programs, and adaptation strategies. This particular report does not include any Indigenous Knowledge or perspectives from Indigenous groups in Canada, but other reports in the National Assessment are expected to incorporate this important and relevant information. An enhanced synthesis of all reports featured in the National Assessment is scheduled for publication sometime in the year 2021.