Report summary

2.2: Synthesis of past changes

Observed climate warming in Canada and its causes

Key message 2.1

Canada is warming in all regions and seasons. Canada warmed by 2.0°C during the 1948–2023 period (very likely 0.9–3.1°C), with northern regions experiencing warming of 2.6°C (very likely 1.4–4.1°C) and generally more warming occurring in winter than in summer.

Key message 2.2

Human influence has warmed Canadian average 2015−2024 temperatures to a level that is 2.2°C (likely 1.8–2.6°C) above that in the pre-industrial era, which is double the amount of warming in the global average temperature that is attributable to human influence when comparing 2010−2019 with global average temperatures in the pre-industrial era (high confidence). The observed warming in Canada of 2.0°C from 1948 to 2023 is very strongly dominated by human influences and indistinguishable from the warming that can be attributed to external influences on the climate (very high confidence).

Observed climatic effects of warming in Canada

Key message 2.3

Most observed climate changes across Canada—on land, in the oceans around Canada, and in the atmosphere—are consistent with a warming climate. Emissions of greenhouse gases from human activity provide the only plausible explanation for this collective change (very high confidence).

Key message 2.4

The observed occurrence in summer of longer growing seasons, increased building cooling requirements, and higher hot temperature extremes are all consistent with a warming climate, as is the occurrence in winter of reduced building heating requirements and less severe cold temperature extremes. Fire seasons have become longer (high confidence), and the area burned in wildfires has increased (medium confidence). The warming climate has also led to substantial changes in the water cycle and cryosphere (very high confidence), as indicated by increased annual precipitation and intensified precipitation extremes, snow cover and glacier mass reductions, earlier spring streamflow in rivers, decreasing lake and river ice, and thawing permafrost.

Key message 2.5

The effects of the warming climate are also clearly seen in Canada’s ocean areas, through increases in ocean water temperature, more frequent marine heatwaves, freshening of near-surface ocean waters, and decreasing sea ice cover, which has resulted in increasing ocean wave heights in the Arctic (high confidence). Some of Canada’s coastal areas are also experiencing the effects of sea-level rise (very high confidence) and more frequent extreme sea-level events (high confidence), which can contribute to coastal flooding. The oceans around Canada have also absorbed anthropogenic carbon dioxide from the atmosphere, which has resulted in ocean acidification in the ocean’s near-surface layers (very high confidence).

2.4: Past temperature changes

Key message 2.6

Canada’s climate has warmed rapidly over the past 75 years. Warming rates have fluctuated over the past century. Annual mean temperatures are estimated to have increased at a rate of 0.26°C (very likely 0.12–0.41°C) per decade between 1948 and 2023 for Canada as a whole and 0.35°C (very likely 0.18–0.55°C) per decade for Canada’s North^{Footnote 3} . Canada’s estimated annual average temperature has exceeded the 1961–1990 average in 30 of the 33 years since 1990.

Key message 2.7

Canada has warmed more quickly than most of the rest of the world. Canada’s warming rate over the 1948–2023 period is similar to that for the global land area (high confidence), but Canada’s North has warmed at a rate that is more than twice the rate for the global land and ocean area combined over the 1948–2023 period (high confidence). Most of the observed warming has occurred since 1970. Canada’s warming rate was almost twice the global warming rate over the 1970–2023 period (high confidence).

Key message 2.8

Human influence has warmed Canadian average temperatures during the 2015–2024 period to a level that is 2.2°C (likely 1.8–2.6°C) above the pre-industrial era (approximated in this report as the period from 1850 to 1900). Human influences acting on their own would likely have caused more warming than the observed warming of 1.6°C between the decades of 1948−1957 and 2014−2023, with natural external influences and internal climate variability combined preventing a small portion of that influence from being realized (high confidence).

2.5: Past precipitation changes

Key message 2.9

Annual total precipitation has increased in Canada since 1949, with larger percentage increases in northern Canada (very high confidence). Annual total precipitation has increased much faster in Canada than for the global land area as a whole over a similar period (very high confidence).

Key message 2.10

Annual precipitation in Canada increased by 9.7% (likely 7.0–12.3%) in Canada as a whole, by 18.9% (more likely than not 8.6–29.5%, medium confidence) in Canada’s North, and by 7.5% (likely 2.4–11.8%) in Canada’s South between 1949 and 2023, with most of the increase attributable to human influence on the climate (medium confidence).

Key message 2.11

Precipitation has not changed uniformly in all seasons. Precipitation has increased in a zonal band centred at 62°N latitude in summer, and in most areas in British Columbia and along the St. Lawrence River in spring and fall (medium confidence). Precipitation has increased in all seasons in an area from southern Nunavut to the Arctic Archipelago and from Labrador to northeastern Quebec (low confidence).

Key message 2.12

The annual snowfall amount and annual number of days with snowfall are estimated to have decreased at most stations in Canada’s South but increased at most stations in Canada’s North (medium confidence). Both the proportion of precipitation days with snow and the proportion of precipitation amount falling as snow have decreased across most of Canada (medium confidence).

2.6: Past wind speed changes

Key message 2.13

Annual and seasonal average surface wind speeds decreased during the 1953–2023 period across a large part of southern Canada stretching from the southern Prairies to central Quebec (medium confidence). In contrast, average wind speeds increased in British Columbia in spring and summer (low confidence). There is low confidence overall in assessments of the magnitude of annual average wind speed changes due to inconsistency between observational data products. It is currently not possible to attribute any aspect of the observed wind speed changes to human influence on the climate system.

Key message 2.14

The sparseness of station data in northern Canada makes it very difficult to assess long-term wind speed trends in that region, but consistency between the available station data and a modern reanalysis dataset suggests that wind speeds increased during the 1953–2023 period in northern Canada (low confidence), particularly in fall and spring.

3.2: Synthesis of projected changes

Canada’s near-term future climate

Key message 3.1

In the near term, Canada will continue warming at close to twice the global rate, with an increase of about 0.9°C (0.2–1.6°C) from 2021 to 2040 in all emissions scenarios (high confidence). On average over this 20-year period, Canada is projected to be 2.7°C (1.8–3.6°C) warmer (high confidence) and receive 7% (5–10%) more precipitation (medium confidence) compared to the 1850–1900 average. Trends already observed, towards more frequent hot extremes, earlier peak streamflow, warmer and more acidic waters around the coasts, and increasing area burned by wildfire, are projected to continue (high confidence). The duration of snow, sea ice, and lake ice cover in Canada will shorten with every increment of global warming (very high confidence).

Canada’s long-term future climate under current global climate policies

Key message 3.2

Climate change in Canada will intensify through the century if emissions continue on a path approximately consistent with current global climate policies (high confidence). In 2081–2100, average warming across Canada relative to 1850–1900 is projected to reach 5.0°C (3.8–6.6°C) (high confidence), and precipitation is projected to increase by 13% (9–18%) (medium confidence). The intensity and frequency of heavy precipitation are projected to increase (high confidence). There is medium confidence that atmospheric rivers will strengthen. Glaciers in western Canada are projected to lose more than 75% of their mass (medium confidence), and permafrost thaw in northern Canada will continue (very high confidence).

Canada’s long- term future climate in a net-zero world

Key message 3.3

Most aspects of Canada’s climate will stabilize in the second half of this century if global CO₂ emissions immediately start to decline and reach net zero in the 2070s (high confidence). Under such a scenario, Canadian temperatures are projected to warm by about 0.8°C between the 2021–2040 and 2081–2100 periods, reaching 3.5°C (2.3–4.8°C) above 1850–1900 average temperatures (high confidence). However, because of slow response times, sea level in most coastal areas is projected to continue to rise, glaciers to continue to melt, and permafrost to continue to thaw through the century, even after surface temperatures stabilize (high confidence).

Canada’s long-term future climate in a world with no climate policies

Key message 3.4

Climate change will continue to intensify strongly in all regions of Canada if emissions continue to rise throughout the century (high confidence), which would reflect a scenario in which current global climate policies are rolled back or fail to mitigate global emissions. In 2081–2100 under this scenario, Canadian temperatures are projected to increase to 6.9°C (5.2–8.9°C) above the 1850–1900 average (high confidence). Precipitation is projected to increase on average by 17% (12–24%) for Canada as a whole (medium confidence), with larger increases in the intensity and frequency of heavy precipitation events than under the current-policies scenario (high confidence). Atmospheric rivers over Canada are projected to strengthen (high confidence), while summer drought is projected to intensify in southern Canada (high confidence). With higher warming levels, the duration of snow, sea ice, and seasonally frozen ground in Canada is projected to shorten even more than under current global climate policies, and glacier melt, permafrost thaw, and sea level rise along most of Canada’s coasts are projected to be higher (high confidence).

3.3: Climate projections and their uncertainties

Key message 3.5

Uncertainties in climate projections result from uncertainties in future emissions of greenhouse gases and other climate change drivers, uncertainties in how the climate system will respond to those changes, and internal climate variability. The range of plausible future global emissions has shifted towards lower emissions scenarios, partly because of developments in global policy and technology (medium confidence). For each emissions scenario, climate response uncertainty has narrowed, owing to improved synthesis of climate models and observations (high confidence). Some internal variability in Canadian climate can now be predicted for periods of up to five years (medium confidence), reducing this source of uncertainty in estimates of near-term climate.

3.4: Temperature

Key message 3.6

Average surface air temperature is projected to increase across Canada in all seasons (very high confidence). The projected warming for Canada based on new techniques and climate models is higher than assessed in the first (2019) edition of Canada’s Changing Climate Report for nominally equivalent scenarios (high confidence).

Key message 3.7

Under a current-policies scenario, annual average temperature is projected to increase by 5.0°C (3.8–6.6°C) relative to 1850–1900 by 2081–2100 (high confidence), with larger increases in northern Canada in winter that could exceed 10°C in some regions (medium confidence). Under a no-policies scenario, average warming for Canada is projected to reach 6.9°C (5.2–8.9°C) by the same period (high confidence). Under a net-zero scenario, annual average temperature for Canada is projected to stabilize after 2050, reaching 3.5°C (2.3–4.8°C) above 1850–1900 levels in 2081–2100 (high confidence).

3.5: Precipitation

Key message 3.8

Winter and annual average precipitation are expected to increase everywhere in Canada, especially in northern Canada and around Hudson Bay (high confidence). Summer average precipitation is expected to increase in northern Canada (medium confidence) and decrease in parts of southern Canada (low confidence). Annual average precipitation is projected to increase for Canada as a whole by 10% (7–15%) under a net-zero scenario, 13% (9–18%) under a current-policies scenario, and 17% (12–24%) under a no-policies scenario by 2081–2100 relative to 1850–1900 (medium confidence). Increases in winter precipitation could exceed 50% in parts of Nunavut and Nunavik (northern Quebec) in the current-policies scenario (medium confidence).

Key message 3.9

Annual snowfall is projected to increase in northern Canada, but it is projected to decrease in southernmost Canada, particularly in coastal regions (medium confidence). This pattern reflects an increase in precipitation everywhere in Canada but warming causing less of it to fall as snow in southernmost regions. Under current-policies and no-policies scenarios, freezing rain is projected to become more frequent over much of Canada, but less frequent over Atlantic Canada and southern Ontario (medium confidence), driven by changes in the simultaneous occurrence of freezing conditions at the surface and warmer air aloft.

3.6: Average near-surface wind

Key message 3.10

Average near-surface wind speed and wind power potential are projected to decrease for Canada (low confidence). Wind speed projections for Canada are highly uncertain due to low model agreement.

4.2: Arctic amplification

Key message 4.1

The Arctic (the region north of the Arctic circle) has warmed at more than three times the rate of the global average over the past five decades (high confidence). Most of this increased warming, known as Arctic amplification, is caused by human influence (high confidence) and involves local climate processes and feedbacks, including sea ice loss. It largely explains why Canada has warmed nearly twice as fast as the global average and the Canadian Arctic three times as fast for the period 1970-2023 (high confidence).

Key message 4.2

Arctic amplification, and the greater rate of warming in Canada’s Arctic compared to the rest of Canada, will continue over the 21st century (very high confidence). In the coming decades, the Canadian Arctic is projected to warm at more than twice the rate of the global average (medium confidence).

4.3: Jet streams, storm tracks, and atmospheric modes of variability

Key message 4.3

Changes in recent decades in the jet streams and storm tracks that affect Canada are small and seen only in limited seasons and regions. There is low confidence in any human influence on these past changes. An overall poleward shift in the jet streams and storm tracks is projected by the end of the 21st century, but the changes are small and depend on the region and season (low confidence).

4.4: Extratropical storms and atmospheric blocks

Key message 4.4

Changes in recent decades in the frequency and intensity of extratropical storms and of atmospheric blocks are uncertain. There is low confidence in any human influence on these past changes. A poleward shift in extratropical storms and a decrease in the frequency of summer extratropical storms are projected over Canada (low confidence). Atmospheric blocks are projected to occur less frequently over Canada, but there are large regional variations (low confidence).

4.5: Atmospheric rivers

Key message 4.5

The frequency and intensity of atmospheric rivers have increased for Canada as a whole in recent decades (medium confidence). However, there is very low confidence in the magnitude of these increases due to the limited number of studies and the sensitivity of results to how atmospheric rivers are defined and detected. There is insufficient evidence to attribute long-term trends for Canada as a whole to human influence. However, human influence has increased the likelihood of extreme atmospheric-river events in southern British Columbia (low confidence). 

Key message4.6

The frequency and intensity of atmospheric rivers over Canada will increase in the future in high emissions scenarios (high confidence) and intermediate emissions scenarios (medium confidence). However, the magnitude of these increases is uncertain.

4.6: North Atlantic hurricanes

Key message 4.7

The strength and associated precipitation rates of North Atlantic hurricanes have increased (medium confidence). However, since only a small proportion of Atlantic hurricanes affect Canada, there is low confidence in the degree to which these changes have affected eastern Canada.

Key message 4.8

The average precipitation rates, maximum precipitation rates, and peak wind speeds associated with North Atlantic hurricanes, as well as the proportion of hurricanes in the North Atlantic that reach categories 4 and 5, are projected to increase (high confidence). However, regarding the small number of hurricanes affecting Canada, there is medium confidence in increasing precipitation rates and low confidence in increasing wind speeds. Changes in frequency of hurricanes affecting Canada are uncertain.  

4.7: Large-scale environmental conditions favouring thunderstorms

Key message 4.9

There is low confidence that large-scale environmental conditions favouring thunderstorms in Canada have changed over the past several decades. This is due to a lack of regional studies for Canada, the weak, conflicting trends across different environmental-condition indicators and data products, and large internal climate variability.

Key message 4.10

Large-scale environmental conditions favouring thunderstorms are projected to become more prevalent across central and eastern Canada in spring, summer, and fall (high confidence). However, there is low confidence that thunderstorms and other severe weather events will increase, because an increase in favourable environmental conditions does not always lead to more thunderstorms.

4.8: El Niño-Southern Oscillation and other atmosphere-ocean coupled modes of variability

Key message 4.11

The El Niño–Southern Oscillation (ENSO) is the dominant source of year-to-year climate variability in western Canada. Year-to-year climate fluctuations associated with ENSO have been larger since 1950 than in the previous century (medium confidence). However, there is low confidence that this change is due to human-caused climate change because internal climate variability is large.

Key message 4.12

The El Niño–Southern Oscillation (ENSO) will remain the dominant source of climate variability in western Canada in the 21st century (high confidence), but there is low confidence in projected changes in year-to-year climate fluctuations associated with ENSO. While climate models consistently show that by the end of the century, the effect of ENSO on winter climate fluctuations will extend into central and eastern Canada, there is low confidence in these projections due to systematic climate model biases.

4.9: Ocean circulation

Key message 4.13

The primary large-scale ocean current system affecting climate in Canada is the Atlantic Meridional Overturning Circulation (AMOC). A weaker than normal AMOC is associated with cooler and drier than normal winters over eastern Canada. There is high confidence that a temporary weakening of the AMOC between 2007 and 2015 led to a period of cooler North Atlantic Ocean surface temperatures and low confidence that this AMOC weakening can be attributed to human influence.

Key message 4.14

There is high confidence that the Atlantic Meridional Overturning Circulation (AMOC) will gradually weaken over the remainder of the 21st century due to human influence, and that this will slightly reduce the warming of eastern and northern Canada. However, the possibility that the AMOC could shut down, leading to a more pronounced regional cooling influence, cannot be ruled out. There is medium confidence that the AMOC will not shut down in the 21st century.

4.10: Synthesis of changes in atmosphere-ocean processes and phenomena

Key message 4.15

Changes that are due to thermodynamic processes are generally robust and well understood.

Key message 4.16

Regional variations in Canadian climate depend strongly on changes in dynamical processes, which are uncertain and less well understood.

Key message 4.17

There is generally more confidence in future human-caused changes than in the attribution of past changes to human-caused climate change.

5.2: Atmospheric component of the water cycle

Key message 5.1

The atmospheric component of Canada’s water cycle has been altered and will continue to be altered by human influence (medium confidence). Total annual precipitation has increased and is projected to continue to increase (high confidence). While there is only low to medium confidence in observed increases in the frequency and intensity of different types of heavy precipitation, there is high confidence these will increase in the future. Warm-season evaporation has increased and is projected to continue to increase across much of Canada, including over open water because of longer ice-free periods (low confidence). The 0°C air temperature isotherm (constant temperature line) is projected to move farther north and to higher elevations across Canada (medium confidence), which is expected to result in changes in the proportion of rainfall versus snowfall.

5.3: Streamflow magnitude and timing

Key message 5.2

The greatest changes in streamflow magnitude across Canada have occurred and are projected to continue to occur on a seasonal basis. During the last 50 to 70 years, streamflow amounts have increased in winter and spring, and in some areas have decreased during summer (high confidence). Winter increases are projected to continue across the entire country, while summer decreases are projected across western Canada (high confidence).

Key message 5.3

Annual streamflow amounts have increased in regions of northern Canada dominated by permafrost and will continue to do so (high confidence). No long-term historical or projected changes in annual streamflow are evident across the rest of the country (high confidence).

Key message 5.4

The timing of spring peak streamflow has shifted across Canada to earlier in the season because of the earlier onset of spring freshets. This shift has resulted in changes from more snowmelt-dominated streamflow regimes to rainfall-dominated regimes. These changes are projected to continue (high confidence).

Key message 5.5

Over the period of observation, there is no indication of long-term changes in water levels in lakes and wetlands for Canada as a whole, and considerable regional and temporal variability is apparent. Levels are projected to decrease in some regions and increase in others (medium confidence) because of the many complex factors that affect surface water storage. These factors include ice cover duration, open-water evaporation, increased precipitation, and permafrost thaw and associated lake drainage or lake expansion.

Key message 5.6

Groundwater recharge is anticipated to occur earlier in the year across the country, largely because of earlier snowmelt and more winter rain events (high confidence). The greatest changes in groundwater systems are expected to occur in northern Canada because of thawing permafrost, which may result in new groundwater pathways (medium confidence). This would allow more interaction between deeper groundwater and surface water systems with possible effects on surface water quality.

Key message 5.7

Groundwater is expected to remain one of the more resilient freshwater resources in a changing climate in comparison to surface water (medium confidence), given its naturally slow flow and enormous storage capacity, and if extraction through pumping does not markedly increase. 

5.6: Droughts

Key message 5.8

Meteorological and agricultural droughts are projected to be longer and more frequent and intense across central and southern Canada during summer, and to be more prominent with higher amounts of global warming and at the end of the century (high confidence). Summer hydrological droughts are also projected to be longer and more frequent and intense in many regions of southern Canada, mainly because of increased evaporation and lower runoff from mountainous regions (low confidence). Historically, periodic droughts have occurred across much of Canada, but no long-term changes in their frequency are detectable (high confidence).

5.7: Floods

Key message 5.9

Over the period of observation, there have been no consistent trends in streamflow flood events across the country (high confidence). Streamflow-related floods in Canada are driven by multiple factors, including extreme precipitation, rapid snowmelt, rain-on-snow events, and ice jams, with complex interactions among these drivers.

Key message 5.10

Projected increases in extreme precipitation are expected to lead to more frequent and intense flash flooding across Canada (high confidence). Warmer temperatures are expected to lead to the earlier occurrence of snowmelt, rain-on-snow events, and ice jam breakups, resulting in earlier streamflow-related spring floods (medium confidence). However, their future frequency remains uncertain because of the interactions among rising temperatures, reduced snow cover, and the complex dynamics of ice jam–related and snowmelt-related floods. 

5.9 Synthesis of water cycle changes

Key message 5.11

There has been a shift in the timing of many water cycle–related processes to earlier in the spring (high confidence). The shifts include earlier occurrences of snowmelt, spring freshet, groundwater aquifer recharge, and freshwater ice-free dates. These changes are projected to continue (high confidence) with possible consequences for future freshwater security.

Key message 5.12

Canada’s water cycle has been altered and will continue to be altered by climate warming (medium confidence). This involves more precipitation, changes in the proportion of rainfall versus snowfall, increases in warm-season evaporation, and a greater potential for flash flooding and summer drought. These changes are expected to directly impact the availability of surface and subsurface freshwater across Canada. 

6.2: Terrestrial snow

Key message 6.1

Snow cover duration has shortened in Canada as a whole over the past four decades (high confidence). Snow cover duration has shortened in northern Canada, southern Ontario, and parts of eastern Canada by one to four weeks, while snow cover duration has lengthened across central Canada by one to four weeks (medium confidence). This regional variability is also reflected in changes in peak snowpack amounts over the past four decades (high confidence).

Key message 6.2

Snow cover duration is projected to shorten across all of Canada and peak snowpack amounts are projected to decrease across most of Canada with increasing climate warming (very high confidence). Unlike the rest of Canada, the western and central parts of northern Canada are projected to experience larger peak snowpack amounts due to increased snowfall despite a shorter projected snow season (medium confidence).

Key message 6.3

Past amounts and changes in snowpack are more uncertain for mountainous regions than elsewhere (high confidence). In a warmer climate, mountainous regions in Canada are expected to have less snowpack accumulation and experience more mid-winter melt events, changing the timing and reducing the predictability of Canadian water resources (high confidence).

6.3: Sea ice

Key message 6.4

Sea ice cover has declined in Canadian waters over the past four to five decades (very high confidence). Regions once covered by thick, multi-year sea ice are now covered by thinner seasonal sea ice that melts every summer (very high confidence). Landfast ice cover, which provides habitat for wildlife and is important for transportation, hunting, and the culture of northern communities, has also declined across the Canadian Arctic and Hudson Bay region (high confidence).

Key message 6.5

The transport of sea ice from the central Arctic Ocean into Canadian Arctic waters has increased over the past two and a half decades (high confidence). This increased transport of sea ice out of the central Arctic Ocean depletes its reserves of thick, multi-year sea ice, while the corresponding flow of multi-year ice into southern Canadian Arctic waters, such as the Northwest Passage, creates hazardous conditions for shipping.

Key message 6.6

The sea ice–free period is projected to lengthen further across Canadian Arctic and Hudson Bay waters with increasing climate warming (very high confidence). In regions with seasonal sea ice cover, the number of ice-free days is projected to increase by approximately one month for each degree of global warming, with smaller increases in the Labrador Sea and larger increases in the Beaufort Sea (medium confidence). The transport of multi-year ice into the Northwest Passage is projected to continue beyond mid-century thereby continuing to limit the shipping season (medium confidence).

6.4: Lake and river ice

Key message 6.7

Lake ice duration has shortened in Canada as a whole over the past four decades (high confidence). Lake ice duration has shortened in northern Canada, British Columbia, southern Ontario, and parts of Atlantic Canada by one to four weeks, while lake ice duration has lengthened across central Canada by up to two weeks (medium confidence). The timing of river ice breakup during spring has changed in response to temperature, and the number of mid-winter breakups is increasing in Canada (medium confidence).

Key message 6.8

Lake ice duration is projected to shorten across Canada as climate warming increases, leading to corresponding decreases in maximum ice thickness (very high confidence). River ice duration and thickness are also expected to decrease generally with increasing climate warming (high confidence), but there is low confidence that such changes will be consistently accurate for individual rivers.

6.5: Glaciers

Key message 6.9

All glaciers in western Canada and the Canadian Arctic have thinned and lost mass over the past two and a half decades, as shown by satellite measurements with comprehensive spatial coverage (very high confidence). Longer-term field measurements on a small number of reference glaciers show that glaciers in Canada have been losing mass since at least the 1960s, and that the rate of loss has accelerated in recent decades (high confidence). In western Canada, declines in glacier contributions to summer streamflow have been observed in several watersheds (high confidence), marking an irreversible decrease in a critical source of freshwater for these regions.

Key message 6.10

Canada’s glaciers are projected to continue losing mass under every future emissions scenario (very high confidence). In western Canada, more than 55% of glacier ice is predicted to disappear by 2100, even if global warming is limited to 2°C (high confidence). The number and severity of glacier-related hazards, such as flooding and landslides, are expected to increase, particularly in western Canada (medium confidence). Melt water from glaciers and ice caps in the Canadian Arctic will continue to be among the largest glacier sources of global sea-level rise up to and beyond 2100 (very high confidence).

6.6: Seasonally frozen ground

Key message 6.11

The annual number of days with seasonally frozen ground has decreased in Canada over the past four decades (high confidence). At locations without underlying permafrost, decreases in the depth of seasonal freezing are expected to have occurred, while at most locations with underlying permafrost,increases in the depth of seasonal thawing are expected to have occurred (medium confidence), but the limited number of observations prevent direct assessment of such changes.

Key message 6.12

The annual number of days with seasonally frozen ground, and the maximum annual depth of seasonally frozen ground outside permafrost areas, are expected to decrease across Canada until mid-century before stabilizing under a low emissions scenario (high confidence). In contrast, these indicators of seasonally frozen ground are expected to continue declining until the end of century and beyond under emissions scenarios with higher levels of carbon emissions and increasing global temperatures (high confidence).

6.7: Permafrost

Key message 6.13

Permafrost at monitored locations in northern Canada has warmed and thawed since the 1980s (very high confidence). Landscapes in the parts of northern Canada with ice-rich terrain have changed in response to climate-driven permafrost thaw (very high confidence).

Key message 6.14

Permafrost warming and thaw-driven landscape changes are expected to continue with increased climate warming (very high confidence). Even if the climate stabilizes, some thawing will continue at depth (very high confidence). However, there is low confidence regarding the magnitude and timing of these changes because of the influence of local ground characteristics.

6.8: Synthesis

Key message 6.15

Coherent changes across many components of the cryosphere are evident both globally and across Canada.

Key message 6.16

The evidence for formal attribution of changes in the cryosphere to human influence, and for correlations between cryospheric and temperature signals, has strengthened. Because air temperature exerts the dominant control on many components of the cryosphere, human-caused climate change is certain to be influencing widespread changes in the cryosphere in Canada.

Key message 6.17

Changes in all components of the cryosphere are projected to worsen or intensify with additional global warming, but limiting the increases in global average temperature will limit these changes.

7.2: Ocean temperatures

Key message 7.1

Ocean temperatures around Canada have increased in ice-free periods since the mid-20th century (high confidence). This increase is consistent with the warming observed in the global upper ocean, for which human influence is extremely likely to be the main driver. The largest increase in annual average sea surface temperatures has been observed adjacent to southern Atlantic Canada (high confidence). By season, the greatest warming has occurred in summer and extends throughout the ocean bordering eastern Canada, including Hudson Bay (high confidence).

Key message 7.2

Continued warming is projected for the oceans around Canada, with the magnitude increasing with higher greenhouse gas emissions (high confidence). The increase in annual average sea surface temperatures is expected to be greater in the waters next to Atlantic Canada and British Columbia than in the Arctic (medium confidence). During the summer period, sea surface temperatures are expected to increase the most in the Beaufort Sea and Hudson Bay, in part due to the decline of seasonal sea ice cover there (medium confidence).

Key message 7.3

More frequent and intense marine heatwaves have been observed in the Pacific and Atlantic oceans around Canada since the 1980s and are expected to continue to increase in all oceans, including the Arctic, because of human-caused climate change (high confidence).

7.3: Ocean salinity and stratification

Key message 7.4

The surface waters of the oceans around Canada are characterized by relatively low salinity and have become even fresher since the 1950s (high confidence). The increasing freshwater input to these oceans results from warming-driven increases in precipitation and runoff from land, which includes glacier and ice sheet meltwater (high confidence). Ocean freshening is projected to continue throughout the 21st century; however, the limited number of emissions scenarios studied and the variability among model projections have resulted in low confidence for the Arctic and medium confidence for the Atlantic and Pacific.

Key message 7.5

Increased stratification, or layering of the upper ocean according to water density, in the northeast Pacific and southern Atlantic Canada regions has resulted from warming and freshening of the sea surface (high confidence). Increased stratification reduces the vertical mixing of nutrients and other chemical compounds in the upper ocean, which is an important process in the marine ecosystem.

7.4: Global and relative mean sea level

Key message 7.6

Global mean sea level has risen by about 20 cm since 1900 as a result of human influence on the climate system (very high confidence). The main contributions to this rise have been thermal expansion of the warming ocean and widespread melting of ice on land, which results in runoff into the ocean (very high confidence). In regions of Canada where the land is subsiding, the relative mean sea level has risen more than would be expected from global sea level rise alone (very high confidence). Rates of up to 34 cm per century in southern Atlantic Canada and the western Arctic have been observed, with smaller rates in British Columbia (very high confidence). In contrast, the sea level in western Hudson Bay has fallen by 88 cm per century, owing to rapid land uplift (very high confidence). Land uplift and subsidence are caused by the continuing adjustment of the land surface, due to the loss of ice mass after the last continental glaciation.

Key message 7.7

Global mean sea level is projected to rise by many tens of centimetres in the 21st century under a low emissions scenario and is unlikely to be more than a metre under a very high emissions scenario (medium confidence). Relative sea levels in different parts of Canada are, however, projected to rise or fall depending on local vertical land motion as well as the amount of global sea-level rise. Owing to land subsidence, parts of Atlantic Canada and the western Arctic are projected to experience increases in relative sea level that are larger than the change in the global mean sea level during the coming century (high confidence).

7.5: Waves and storm surge

Key message 7.8

Mean and extreme wave heights have increased in Arctic and sub-Arctic regions, primarily as a result of the warming-driven reduction in sea ice (high confidence). Wave heights in the northwest Atlantic have also increased over the last few decades (medium confidence), but the changes in ice-free areas that would result in increased wave heights cannot be directly attributed to human-caused climate change. Wave height trends in the northeast Pacific are not statistically significant. Extreme storm surges have increased in areas of the western Arctic, Hudson Bay, and Atlantic Canada (low confidence).

Key message 7.9

The projected lengthening of the Arctic ice-free season will cause increases in mean and extreme wave heights (high confidence) and storm surges (medium confidence). In areas of Atlantic Canada not affected by sea ice, mean wave heights are projected to decrease (medium confidence), while weak changes are projected in the northeast Pacific (low confidence). Projections of extreme wave heights in areas without sea ice provide limited evidence of increases in Atlantic Canada (low confidence).

7.6: Extreme sea level

Key message 7.10

Extreme sea-level events have increased in frequency and magnitude in places along Canada’s coastline where the relative sea level has risen over the past century, such as southern Atlantic Canada, the western Arctic, and British Columbia (high confidence).

Key message 7.11

Extreme sea-level events are projected to occur more often and to become larger because of future increases in relative sea-level rise in many parts of Canada (high confidence). The projected decline of sea ice along Canada’s Arctic and Atlantic coasts will result in increased waves and storm surges, which will exacerbate extreme sea-level events (high confidence).

7.7: Ocean chemistry

Key message 7.12

At the surface, observations over the last three decades show that the oceans around Canada have absorbed anthropogenic carbon dioxide from the atmosphere, causing ocean acidification (very high confidence). This higher-carbon, acidified water is carried beneath the surface by ocean circulation.

Key message 7.13

Beneath the surface, oxygen has declined over many decades in the offshore and coastal waters of the northeast Pacific, in the Estuary and Gulf of St. Lawrence, and on the Scotian Shelf (high confidence), but the processes responsible vary by region and are not fully understood. Since biological respiration both consumes oxygen and adds carbon dioxide, acidification is exacerbated in regions experiencing oxygen declines (high confidence). Year-to-year variations in water circulation and biological activity have caused extreme low-oxygen and high-acidity events in the subsurface oceans around Canada (medium confidence).

Key message 7.14

Over the rest of the 21st century, the oceans around Canada are projected to continue to absorb anthropogenic carbon dioxide, to increase in acidity (very high confidence), and to lose oxygen in the subsurface (medium confidence). The level of projected acidification in the latter half of this century will strongly depend on the level of future carbon dioxide emissions (very high confidence).

7.8: Synthesis

Key message 7.15

The oceans slow the rate of climate-driven atmospheric warming by absorbing heat and carbon dioxide; however, this absorption, in turn, warms and acidifies the oceans around Canada (very high confidence). Impacts on the ocean include more frequent and intense marine heatwaves, increasing stratification, rising sea levels in many regions, more frequent coastal flooding events, and decreasing ocean oxygen levels (high confidence). Continued emissions will intensify these changes, but with impacts varying substantially along Canada’s coastlines, which will result in differing needs for climate change adaptation (high confidence).

8.2: Temperature extremes

Key message 8.1

The intensity and frequency of hot extremes in Canada as a whole and in multiple regions have increased since the mid-20th century (high confidence). The intensity and frequency of cold extremes in Canada as a whole and in all Canadian regions have decreased since the mid-20th century (high confidence). Human influence on the climate is the dominant driver of the observed warming of both hot and cold extremes (high confidence).

Key message 8.2

Increases in the intensity and frequency of hot extremes and decreases in the intensity and frequency of cold extremes are projected for all regions of Canada, with changes becoming larger as global mean temperature increases (very high confidence).

8.3: Precipitation extremes

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8.3.1: One-day and five-day total precipitation extremes

Key message 8.3

The intensity and frequency of one-day and five-day precipitation extremes have increased in Canada as a whole since the mid-20th century (medium confidence), consistent with an increase in atmospheric moisture across Canada due to warming. Human influence on the climate is the main driver of the observed intensification of extreme precipitation at the continental scale across North America (high confidence). Increases in the intensity and frequency of one-day and five-day precipitation extremes have been observed with low confidence in many, but not all, regions of Canada since the mid-20th century. These regional changes are uncertain, due to large spatial and temporal variability.

Key message 8.4

Increases in the frequency and intensity of one-day and five-day precipitation extremes are projected for all regions of Canada (high confidence), with changes becoming larger as global average temperature increases (high confidence).

8.3.2: Short-duration rainfall extremes

Key message 8.5

The intensity and frequency of short-duration (i.e., timescales shorter than a day) rainfall extremes have increased for Canada as a whole (low confidence) since the mid-20th century. The lower confidence in shorter-duration precipitation extremes is due to greater spatial and temporal variability, the lower density of observing stations, and shorter length of records. Local and regional changes cannot be assessed with confidence for these same reasons.

Key message 8.6

The intensity and frequency of short-duration rainfall extremes in Canada are projected to increase in the future (high confidence), with the increases becoming larger as global average temperature increases (high confidence). The projected rate of intensification of short-duration rainfall extremes for Canada as a whole is consistent with the rate of increase in atmospheric moisture along with average warming in Canada (medium confidence).

8.3.3: One-day snowfall extremes

Key message 8.7

The intensity and frequency of heavy one-day snowfalls have increased at most locations in northern Canada since the mid-20th century (medium confidence). Under future warming, these heavy snowfall amounts are projected to increase across much of northern and eastern Canada (medium confidence). In southwestern Canada, heavy one-day snowfall amounts have decreased since the mid-20th century (medium confidence), while no clear pattern has been observed in southeastern Canada. There is low confidence in the magnitude and direction of future changes in extreme snowfall events for southern Canada.

8.3.4: Freezing rain extremes

Key message 8.8

There is insufficient evidence to assess historical changes in extreme freezing rain events—those that cause an accumulation of ice sufficient to disrupt infrastructure—in Canada, due to limited observational data and a paucity of studies focusing on historical trends. The frequency of extreme freezing rain is projected to increase in most regions of Canada (low confidence), while some decreases or no significant changes are projected in parts of southern Ontario, the Atlantic provinces, and coastal regions of Hudson Bay (low confidence).

8.3.5: Hail

Key message 8.9

There is insufficient evidence to assess historical changes in severe hail (≥ 2 cm in diameter) for Canada as a whole. Limited studies examining trends in hail of any diameter suggest regionally contrasting patterns, with increasing trends in Alberta and decreasing trends in Saskatchewan and Manitoba over recent decades (very low confidence). Projections indicate a potential increase in the frequency of severe hail across parts of western Canada (very low confidence), but this assessment is based on limited evidence and involves substantial modelling challenges.

8.4: Wind extremes

Key message 8.10

There is insufficient evidence to assess historical changes in extreme winds in Canada due to limited station coverage and representativeness, significant uncertainties in reanalysis products, and the paucity of studies examining trends in wind extremes. There is very low confidence in the direction and magnitude of future changes in extreme winds due to the limited number of studies and the substantial uncertainty related to model projections of wind-related phenomena.

8.5: Water cycle extremes

8.6: Oceans

Key messages for these sections of Ch. 8 are positioned in their home chapters. Chapter 5 assessed changes in the water cycle and Chapter 7 assessed changes in the oceans.

8.7: Compound events

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8.7.1: Fire weather and wildfires

Key message 8.11

The fire season has lengthened in most parts of Canada (high confidence) and is projected to continue to lengthen as the global average temperature increases (high confidence). Fire weather—characterized by hot, dry, and windy conditions conducive to wildfires—has increased in Alberta and British Columbia (medium confidence), with some indications of increases in other regions (very low confidence). The frequency and intensity of extreme fire weather conditions are projected to increase in most regions of Canada as global average temperature rises (high confidence).

8.7.2: Compound coastal flooding

Key message 8.12

Compound coastal flooding arises from jointly occurring climate conditions, such as heavy rain during episodes of extreme water levels. Such co-occurring drivers have increased in frequency and intensity in some parts of Canada, with evidence primarily from Atlantic locations (low confidence), and are projected to become more frequent and intense at locations along the Atlantic, Pacific and Western Arctic coastlines (medium confidence). These projected increases are mostly due to rising sea levels and increases in the frequency and intensity of extreme precipitation events (medium confidence).

8.7.3: Compound wind and rainfall

Key message 8.13

There is insufficient evidence to assess historical changes in compound wind and rainfall events in Canada, due to limited studies focusing on observed trends. Compound extreme wind and rainfall events are projected to increase (medium confidence), driven mainly by the greater frequency of future extreme rainfall, but with very low confidence in the regional pattern and magnitude of changes.

8.7.4: Human-perceived heat stress

Key message 8.14

The intensity and frequency of human-perceived heat stress—which results from the combined effects of high temperatures and humidity—have increased in Canada as a whole (high confidence). Human-perceived heat stress is projected to increase in Canada, driven mainly by increases in air temperature (high confidence).

8.8: Synthesis of the effects of warming on climate extremes

Key message 8.15

Warming has led to increases in the frequency and intensity of hot extremes, human-perceived heat stress, and marine heatwaves, and decreases in cold extremes (high confidence), as well as increases in the frequency and intensity of extreme fire weather conditions and the intensification of heavy precipitation events in Canada (medium confidence), with projections indicating continued and larger changes under higher global warming levels (high confidence).

9.2: Natural global carbon cycle

Key message 9.1

Before the industrial era, carbon stored in fossil fuels had remained isolated for millions of years, playing no discernable role in the exchange of carbon between the land, ocean, and atmosphere (very high confidence).

Key message 9.2

During the last 800,000 years before the industrial era, the atmospheric carbon dioxide concentration varied between 170 and 300 parts per million (very high confidence). For comparison, the atmospheric carbon dioxide concentration for the year 2024 was 423 parts per million.

9.3: Human-caused changes to the global carbon cycle

Key message 9.3

The increase in atmospheric carbon dioxide concentrations since the pre-industrial era has unequivocally been caused by emissions from the burning of fossil fuels and human-caused land-use change. In 2023, annual human-caused global CO₂ emissions reached 41 Gt CO₂/yr (± 3 Gt CO₂/yr) (gigatonnes of carbon dioxide per year); including contributions from other greenhouse gases, total greenhouse gas emissions were 57 Gt CO₂-eq/yr (carbon dioxide equivalent units per year).

Key message 9.4

Based on Canada’s national inventory report, total anthropogenic greenhouse gas emissions for Canada peaked in 2007 at 774 Mt CO₂-eq (megatonnes of carbon dioxide equivalent units). Notable reductions occurred in 2008–2009 during the global recession (714 Mt CO₂-eq/yr) and in 2020 during the COVID-19 pandemic (682 Mt CO₂-eq/yr). Emissions for 2023 (694 Mt CO₂-eq/yr; most recent year reported) are approximately 10% lower than their 2007 peak, despite continued growth in Canada’s population and economy.

Key message 9.5

Land and ocean together have taken up more than half of the global anthropogenic carbon dioxide emissions since the pre-industrial era (very high confidence). The ocean is expected to continue taking up carbon dioxide in the long term (beyond a century), but the land carbon sink may weaken or become a carbon source (high confidence).

9.4: Global climate response to carbon dioxide emissions

Key message 9.6

There is an approximately linear relationship between global warming and cumulative carbon dioxide (CO₂) emissions (high confidence). This relationship implies a limit to the total amount of CO₂ that can be emitted into the atmosphere while keeping warming below a given level (e.g., 2°C).

Key message 9.7

There will be little to no further global warming from carbon dioxide (CO₂) after CO₂ emissions cease (medium confidence).

Key message 9.8

In addition to carbon dioxide (CO₂), other greenhouse gases (non-CO₂ GHGs) in the atmosphere cause global warming. Limiting warming to a specific level requires emissions of long-lived GHGs such as CO₂ to reach net zero and emissions of short-lived GHGs to decline strongly (high confidence).

9.5: The carbon cycle in Canada

Key message 9.9

Carbon in Canada’s oceans is mainly stored in seawater and marine sediments. On land, almost all (about 95%) of the carbon in Canada is stored in soils, including permafrost and peatlands, with the rest (about 5%) stored in vegetation (very high confidence).

Key message 9.10

Since the last Ice Age, there has been a net uptake of carbon by Canada’s land mass. At present (2000–2019), the land continues to be a carbon sink (medium confidence). However, extreme events like the 2023 fire season can cause the land to become a temporary source of carbon (low confidence). In the future, both carbon uptake from increased vegetation growth (medium confidence) and carbon emissions from permafrost thaw, wildfires, and other disturbances (high confidence) are expected to increase. However, their net effect on the carbon balance of Canada’s land ecosystems remains uncertain.

Key message 9.11

The annual forest area burned by fires in Canada has increased since the early 1980s (medium confidence). The area burned is projected to increase further as the climate continues to warm (high confidence).

Key message 9.12

On average, Canada’s oceans (inside the Exclusive Economic Zone) take up carbon dioxide (CO₂) (medium confidence), although some nearshore areas emit CO₂ (low confidence). Overall, Canada’s oceans will continue to take up CO₂, as long as atmospheric CO₂ concentrations continue to increase (medium confidence).

9.6: Nature-based approaches to climate change mitigation

Key message 9.13

Nature-based climate solutions (NBCS) play a complementary rather than a central role in achieving climate change mitigation goals (very high confidence).

Key message 9.14

In Canada, the protection of existing nature-based carbon stocks and carbon dioxide (CO₂) drawdown resulting from the expansion of nature-based carbon sinks is estimated to reach as much as 78 Mt CO₂-eq/yr (CO₂-equivalent units per year) after 10 years of implementation (low confidence).