Graphics

Observed changes (°C) in annual temperature across Canada between 1948 and 2016, based on linear trends. From Chapter 4 Figure 4.3.

Projected annual temperature change for Canada this century under a low emission scenario (RCP2.6) and a high emission scenario (RCP8.5). Projections are based on the Coupled Model Intercomparison Project (CMIP5) multi-model ensemble. Changes are relative to the 1986–2005 period. The thin lines show results from individual models and the heavy line is the multi-model mean. From Chapter 4 Figure 4.8.

Observed changes in annual precipitation across Canada, 1948–2012, based on linear trends. From Chapter 4 Figure 4.15.

Projected annual mean precipitation change (%) this century for Canada under a low emission scenario (RCP2.6) and a high emission scenario (RCP8.5). Projections are based on the Coupled Model Intercomparison Project (CMIP5) multi-model ensemble. Changes are relative to the 1986–2005 period. The thin lines show results from individual models and the heavy line is the multi-model mean. From Chapter 4 Figure 4.19.

Top panels: Projected changes in recurrence time (in years) for annual highest temperatures that occurred, on average, once in 10, 20, and 50 years in the late 20th century across Canada, as simulated by the Coupled Model Intercomparison Project (CMIP5) multi-model ensemble under a low emission scenario (RCP2.6) and a high emission scenario (RCP8.5). Lower panels: Projected changes in recurrence time for annual maximum 24-hour precipitation. From Chapter 4 Figures 4.12 and 4.20.

Terrestrial snow cover fraction and sea ice concentration seasonal trends for 1981–2015. Snow cover fraction is the proportion of time the ground is covered by snow. A decline of 10% per decade indicates a decline of approximately 3 days per month per decade in snow cover. Sea ice concentration is the percentage of area that is covered with sea ice. Stippling indicates statistical significance. Dashed line denotes limit of Canadian marine territory. From Chapter 5 Figure 5.2.

Probability of sea ice–free conditions in Canadian Arctic marine areas by 2050 under a high emission scenario (RCP8.5) from the Coupled Model Intercomparison Project (CMIP5) multi-model mean. 5% sea ice area was used to define ice-free conditions. From Chapter 5 Figure 5.11.

Schematic diagram showing past and future projected changes in the seasonal distribution of streamflow in many snow-fed river basins across Canada. In association with warming temperatures, spring peak streamflow following snowmelt has, and will continue to, occur earlier with higher winter flows and reduced summer flows.

Projected relative (local) sea-level change along Canadian coastlines at the end of the century. Changes in local sea level are a combination of global sea level rise and local land subsidence or uplift. Projections shown are the median projection based on a high emission scenario (RCP8.5) and are relative to the average conditions in the 1986–2005 period. From Chapter 7 Figure 7.16.

Projected annual temperature change for Canada under a low emission scenario (RCP2.6) (left panel) and a high emission scenario (RCP8.5) (right panel) for the late century. Projections are based on the Coupled Model Intercomparison Project (CMIP5) multi-model ensemble. Changes are relative to the 1986–2005 period. From Chapter 4 Figure 4.8.

These six regions are defined by the political boundaries of the provinces and territories of Canada and match the regions analyzed in Canada’s Third National Assessment. The North region includes Yukon, Northwest Territories, and Nunavut. The Prairie region includes the provinces of Alberta, Saskatchewan, and Manitoba. The Atlantic region includes the provinces of New Brunswick, Nova Scotia, Prince Edward Island, and Newfoundland and Labrador. The remaining three regions encompass single provinces only (British Columbia, Ontario, and Quebec).

The confidence levels and likelihood statements used in this report are the same as those used in the IPCC Fifth Assessment Report (IPCC, 2013). Generally, evidence is most robust when there are multiple, consistent independent lines of high-quality evidence. A level of confidence is expressed using five qualifiers: very high, high, medium, low, and very low. The figure depicts summary statements about evidence and agreement and their relationship to the confidence scale. The relationship is flexible, with “fuzzy boundaries” between difference confidence levels. The categories of likelihood are also considered to have fuzzy boundaries. For example, a statement that a result is likely means that the probability of its occurrence ranges from over 66% to 100%. This corresponds to a chance of the event occurring of two-thirds or more.

Departure (anomaly) of global mean annual surface temperature from the average over the 1961–1990 reference period, from three datasets. The grey shading indicates the uncertainty in the dataset produced by the Met Office Hadley Centre and the Climatic Research Unit at the University of East Anglia, UK (HadCRU).

Multiple indicators of a changing global climate from independently derived estimates. Datasets in each panel have been normalized to a common period of record.

The sun is the source of energy for Earth (1). Some of the sun’s energy is reflected back to space (2), but the rest is absorbed by the atmosphere, land, and ocean and re-emitted as longwave radiation (radiant heat). Some of this radiant heat is absorbed and then re-emitted by greenhouse gases in the lower atmosphere, trapping heat in the lower atmosphere and reducing how much is radiated to outer space. This process is known as the greenhouse effect (3). Changes to the amount of incoming solar radiation (1), the amount of reflected sunlight (2), and the heat-trapping capacity of the atmosphere (3) cause climate warming or cooling. Factors that drive such changes are called climate drivers or climate forcing agents.

Albedo is a unitless quantity that indicates how well a surface reflects solar energy. Albedo (α) ranges from 0 to 1, with 0 representing a black surface that absorbs 100% of energy and 1 representing a white surface that reflects 100% of energy. The presence of ice, and to a greater extent snow-covered ice, on dark surfaces (such as the ocean) increase albedo.

Atmospheric concentration of carbon dioxide (CO2), oxygen (O2), and 13C/12C stable isotope ratio in CO2 recorded over the last decades at representative stations. Top panel: CO2 (green lines) from Mauna Loa Northern Hemisphere (MLO) and South Pole Southern Hemisphere (SPO) atmospheric stations, and O2 (blue lines) from Alert Northern Hemisphere (ALT) and Cape Grim Southern Hemisphere (CGO). Lower panel: δ13C in CO2 from MLO and SPO. The ratio of the 13C to 12C isotopes, relative to a standard, is measured by δ13C (delta C 13), which is defined as δ13C = [ (13C/12C)sample / (13C/12C)standard − 1 ] × 1000 and has units of permil. Samples with a larger value of δ13C are said to be enriched, while samples with a lower δ13C are said to be depleted.

Canada’s greenhouse gas (GHG) monitoring network (map) and example observations for carbon dioxide (plot) from Alert, Nunavut (upper photo) and Fraserdale, Ontario (lower photo).

Global mean atmospheric concentrations of carbon dioxide (CO2) (yellow and red), methane (CH4) (aqua and navy), and nitrous oxide (N2O) (light and dark blue), based on data from ice cores (dots) and direct atmospheric measurements from the Cape Grim Observatory, Australia (yellow, aqua and light blue lines) and from the Canadian greenhouse gas monitoring site at Alert, Nunavut (red, navy and dark blue lines).

Radiative forcing (RF; the net change in the energy balance of the Earth system due to an external perturbation), based on changes in concentrations of forcing agents, between 1750 and 2011, in units of watts per square metre (W/m2). Hatched bars are radiative forcing (RF), and solid bars are effective radiative forcing (ERF), the RF once rapid adjustments in atmospheric temperatures, water vapour, and clouds to the initial perturbation are accounted for. Uncertainties (5%–95% uncertainty range) are given for ERF (solid horizontal lines [whiskers]) and for RF (dotted whiskers). The total anthropogenic forcing is the sum of the anthropogenic forcing contributions. See description in Section 2.2.

Differences in annual global mean surface temperature (relative to 1961–1990) from three datasets. Radiative forcing due to human activities is shown by the black dashed line.

IPCC AR5 assessed likely ranges (horizontal lines [whiskers]) and their mid-points (bars) for forcings to which global mean warming over the 1951–2010 period can be attributed: well-mixed greenhouse gases, other anthropogenic forcings (dominated by aerosols), combined anthropogenic forcings, natural forcings, and internal variability. The black bar shows the observed temperature trend (HadCRUT4 dataset) and the associated 5% to 95% uncertainty range (whiskers). Bars to the left of 0.0°C indicate an attributable cooling; bars to the right indicate an attributable warming.

Socioeconomic (top row), energy intensity (second row), greenhouse gas emissions (third row), and ultimately greenhouse gas concentration (bottom row) scenarios underlying the Representative Concentration Pathways (RCPs) used to drive future climate projections. The light grey shading indicates the 98th percentile and the dark grey shading the 90th percentile of the underlying databases.

Schematic illustration of the processes included in an Earth system model, and the way in which mathematical equations describing physical processes are solved on a three-dimensional grid.

Historical observations of annual mean surface temperature show that the rate of surface warming for Canada (slope of the blue line) is more than twice the rate of surface warming for the globe (slope of the red line). The rate of warming for the Canadian Arctic (slope of the grey line) is about three times the global rate. Canadian results are based on the Adjusted and Homogenized Canadian climate data (Vincent et al., 2015). The global result is based on the HadCRUT data set (Morice et al., 2012³⁸).

Feedback mechanisms make different contributions to warming, depending on the region of the world. The contributions of lapse-rate, snow/ice albedo, Planck, cloud, and water vapour feedbacks to warming for the Arctic and for the Tropics are shown for a modelled climate state in which carbon dioxide concentrations are quadrupled from their pre-industrial levels. Feedbacks in the red-shaded area of the figure contribute to enhanced warming in the Arctic relative to the Tropics, whereas feedbacks in the blue-shaded area contribute to enhance warming in the Tropics relative to the Arctic.

Global annual mean surface air temperature anomalies from 1850 to 2012 (anomalies are computed relative to the 1961–1990 average shown by yellow shading). The heavy black lines represent three different reconstructions of temperature based on observations. Each of the thin coloured lines represents a simulation from one of 36 climate models. The heavy red line indicates the multi-model average. The overall warming trend is evident in both observations and simulations, particularly since about 1960, and both show cooling following large volcanic eruptions (vertical dashed lines).

The upper panel shows the multi-model annual global mean surface temperature change relative to a historical reference period (1986–2005) for a range of emission scenarios. The shaded bands indicate the 5%–95% spread across the multi-model ensemble. The lower panels show the multi-model mean projected change by late century (the 2081–2100 average minus the 1986–2005 average) for annual (b) mean surface air temperature and (c) precipitation for the low emission scenario (RCP2.6) and the high emission scenario (RCP8.5).

Carbon dioxide concentrations for four different Representative Concentration Pathways (RCPs; upper panel) and the corresponding compatible emissions (lower panel) based on simulations from five different Earth system models (Jones et al., 2013). The high emission scenario (RCP8.5) corresponds to emissions that are more than double those today by the end of the century, whereas the low emission scenario (consistent with temperature stabilization below 2°C) requires emissions to be rapidly reduced to near zero, or even negative, levels well before the end of the century. Note that the IAM scenario curves indicate the emissions obtained from the integrated assessment models that provide the RCP concentrations (see Figure 3.1).

Increases in global mean surface temperature with increasing cumulative carbon dioxide (CO2) emissions (lower axis label refers to emissions in gigatonnes of carbon, upper axis label in gigatonnes of CO2). Coloured lines show multi-model average results from the Climate Model Intercomparison Project (CMIP5) for each Representative Concentration Pathway (RCP) until 2100, and dots show decadal means. Model results over the historical period (1860 to 2010) are indicated in black. The coloured plume illustrates the multi-model spread over the historical and four RCP scenarios. The thin black line and grey area indicate the multi-model mean (line) and range (area) simulated by CMIP5 models resulting from a CO2 increase of 1% per year.

Global mean surface temperature simulated by the CanESM1 model under a scenario of increasing CO2 emissions (black), followed by a cessation of emissions in 2010 (green) and 2100 (red).

Monthly precipitation simulated by the global model (left) and regional model (right) based on simulations described by Scinocca et al. (2016). The global model results are provided to the regional model along its boundaries, and the regional model recomputes climate in the interior of that limited area domain. The higher-resolution regional model provides more detail, as seen in the simulated precipitation patterns.

Location of stations for which long-term precipitation (blue) and temperature (red) observations exist and for which the data have been homogenized (for temperature) and adjusted (for changes in the instruments for precipitation). Over the past two decades, monitoring technology has evolved and the climate observing network has transitioned from manual to automated observations. Procedures are currently under development for joining and adjusting past manual and current automated climate observations in order to preserve continuity for climate monitoring and trend analysis (Milewska et al. 2018; Vincent et al. 2018).

Photos of the observing site Amos, Quebec, taken by inspectors showing the site before 1963 (a) and after 1963 (b). (c) Time series of the difference in the annual mean of the daily minimum temperatures between Amos and a reference station shows a decreasing step in 1927 and an increasing step in 1963, (d) The original (red line) and adjusted (blue line) time series of the annual mean of the daily minimum temperatures. The red dashed line shows an increasing trend of 2.4°C for 1915–1995 in the original series, while the blue dashed line shows an increasing trend of 0.8°C for 1915–1995 in the homogenized data.

Observed changes (°C) in seasonal mean temperatures between 1948 and 2016 for the four seasons. Estimates are derived based on linear trends in the gridded station data.

Changes in the observations (Observed, navy) and in the observed data removing the effects of the Pacific Decadal Oscillation and the North Atlantic Oscillation (Observed*, grey), along with the estimated contribution of all external forcing, anthropogenic forcing, and natural external forcing (effects of solar and volcanic activities) to observed changes in mean (a, b, c) and extreme (d, e, f, g) temperatures for Canada as a whole over the 1948–2012 period. The top panels show the estimations of attributable warming for (a) annual, (b) winter, and (c) summer mean temperatures. The bottom panels show estimates of attributable warming for extreme temperatures, including (d) annual highest daily maximum temperature, (e) annual highest daily minimum temperature, (f) annual lowest daily maximum temperature, and (g) annual lowest daily minimum temperature. The thin black bars indicate the 5%–95% uncertainty range.

The left-hand panel shows Canadian mean temperature change plotted against global mean temperature change (°C for 20-year averages relative to 1986–2005) from fifth phase of the Coupled Model Intercomparison Project (CMIP5) model simulations for three different forcing scenarios (green: RCP2.6; blue: RCP4.5; red: RCP8.5). Heavy lines are least-squares linear fits, whereas thinner dashed lines are individual model results. The right-hand panel shows the changing length of the growing season (in days, see Chapter 1, Section 1.2) for warm-season crops in the Canadian Prairies, as a function of changes in Canadian mean temperature.

Observed changes in: (a) annual highest daily maximum temperature, (b) annual lowest daily minimum temperature, (c) annual number of hot days (when daily maximum temperature is above 30°C), (d) length of growing season, and (e) heating and (f) cooling degree days. Changes are computed based on linear trends over the 1948–2016 period. Filled triangles indicate trends significant at the 5% level. The black dots on (c) and (f) mark stations where hot days or daily mean temperature above 18°C do not normally occur. The legend may not include all sizes shown in the figure.

Multi-model median projected changes in (a) annual highest daily maximum temperature, (b) annual lowest daily minimum temperature. All maps are based on statistically downscaled and bias-corrected temperature data from simulations by 24 Earth system models. The two left-hand panels show projections for 2031–2050 and 2081-2100 under a low emission scenario (RCP2.6), while the two right-hand panels show projections for 2031–2050 and 2081–2100 under a high emission scenario (RCP8.5).

Projected changes in recurrence time (in years) for annual highest temperatures that occurred, on average, once in 10, 20, and 50 years in the late-20th century across Canada, as simulated by Earth system models contributing to fifth phase of the Coupled Model Intercomparison Project (CMIP5) under a low emission scenario RCP2.6 (upper) and a high emission scenario RCP8.5 (lower).

Multi-model median projected changes in (a) annual number of hot days (days) when daily maximum temperature is above 30°C (TX30), (b) length of growing season for warm-season crops (days) (GSL), (c) cooling degree days (°C-days) (CDD), (d) heating degree days (°C-days) (HDD). All maps are based on statistically downscaled temperature from simulations by 24 Earth system models. The two left-hand panels show projections for 2031–2050 and 2081–2100 under a low emission scenario (RCP2.6), while the two right-hand panels display projections for 2031–2050 and 2081–2100 under a high emissions scenario (RCP8.5), respectively. Areas with less than one hot day per year on average are marked with grey in panel (a), while areas without sufficient cumulative heat during the growing season to support growing warm season crops such as corn or soybean are maked with grey in panel (b).

Projected change in freezing degree days (°C-d) for the period 2031–2050 (upper panels) and 2081–2100 (lower panels) relative to 1986–2005 average, computed from statistically downscaled daily temperatures based on simulations by 24 Fifth Phase of the Coupled Model Intercomparison Project (CMIP5) models (Li et al., 2018). The left-hand panels show results for a low emission scenario (RCP2.6) and the right-hand panels show results for a high emission scenario (RCP8.5).

Observed changes in normalized seasonal precipitation (%) between 1948 and 2012 for the four seasons. Changes are computed based on linear trends over the respective periods. Estimates are derived from the gridded station data. There is a lack of data in northern Canada (see Figure 4.1).

Projected changes in recurrence time for annual maximum 24-hour precipitation that occurs, on average, once in 10, 20, and 50 years in the late century across Canada, as simulated by Earth system models contributing to the fifth phase of the Coupled Model Intercomparison Project (CMIP5) under a low emission scenario (RCP2.6; upper) and a high emission scenario (RCP8.5; lower). The projections are at global climate model resolution, and the processes that produce 24-hour extreme precipitation at local scale are not well represented. Therefore, projections should be interpreted with caution. The shading represents the range between the 25th and 75th percentiles.

The blue distribution represents the possible values of a climate variable in a world without a human influence. The red distribution represents the possible values of the same variable in a world with the human contribution. The shaded areas indicate the probability of experiencing an extreme event (defined by the dashed vertical bar) in each scenario.

Return periods for the observed three-day maximum precipitation (a, b) and three-day maximum runoff (c) that led to the 2013 southern Alberta extreme flooding event. Present-day return periods are shown in red, and return periods from three pre-industrial simulations are shown in blue. Analysis is for the larger southern Alberta region (a) and the smaller Bow River basin (b, c). The box plots show the spread in the return periods across different estimates of the observed values from the reference simulations. The box boundaries indicate the range from the 25th to 75th percentiles, the middle line indicates the 50th percentile, and the whiskers extend to 1.5 times the width of the box or the most extreme value.

Risk ratios for three measures of extreme wildfire risk in the Southern Prairies Homogeneous Fire Regime zone (Boulanger et al., 2014), showing the increase in likelihood due to the anthropogenic contribution. A risk ratio greater than 1 (dashed line) indicates the extreme event is more likely when the human contribution is included. The three measures used to characterize extreme wildfire risk in this region are fire weather (extreme Fire Weather Index), fire behaviour (high number of fire spread days), and fire season (long fire seasons). The error bars represent the 5–95% uncertainty range.

Left: Difference in snow cover duration (SCD) and sea ice cover duration (ICD; upper), and in seasonal maximum snow water equivalent (SWEmax) and sea ice thickness (SITmax; lower) between the periods 2006–2015 and 1981–1990. Right: Time series of cumulative specific volume change (the running total of ice cap surface mass balance divided by ice cap area) for three ice caps in the Canadian Arctic; annual mean ground temperature departure in the sub-Arctic Mackenzie Valley (Norman Wells) and high Arctic (Alert) relative to the 1988–2007 mean; annual maximum lake ice thickness (Great Slave Lake, Northwest Territories and Baker Lake, Nunavut); and annual river discharge summed for rivers draining into the Arctic Ocean from North America and Eurasia.

Terrestrial snow cover fraction and sea ice concentration seasonal trends for 1981–2015. Stippling indicates statistical significance (there is only a 10% possibility that such changes are due to chance). Dashed line denotes limit of Canadian marine territory. Changes in sea ice are discussed in Section 5.3.

Trends in maximum snow water equivalent (SWEmax) (% per decade) for 1981–2015. Stippling indicates statistical significance (there is only a 10% possibility that such changes are due to chance).

Projected terrestrial snow cover fraction and sea ice concentration seasonal trends (% per decade) for the 2020–2050 period for Canadian land and marine areas. Trends are calculated from the multi-model mean of an ensemble of climate models (Coupled Model Intercomparison Project – CMIP5), using a high emission scenario (RCP8.5). Stippling indicates statistical significance (there is only a 10% possibility that such changes are due to chance).

Projected trends in maximum snow water equivalent (SWEmax, % per decade) for 2020–2050 for Canadian land areas. Trends are calculated from the multi-model mean of an ensemble climate models (Coupled Model Intercomparison Project – CMIP5), using a high emission scenario (RCP8.5). Stippling indicates statistical significance (there is only a 10% possibility that such changes are due to chance).

Monthly projected trends in Canadian snow cover extent (top) and snow water mass (bottom) from the Coupled Model Intercomparison Project (CMIP5) multi-model ensemble (blue) and from the Canadian Earth System Model (CanESM) large ensemble (aqua), under a high emission scenario (RCP8.5). Monthly mean observational trends (1981–2015) from the snow dataset used in Section 5.1.1 are shown in red. Boxes show the 25th–75th percentile range, the horizontal line shows the median, and the dashed whiskers illustrate the minimum and maximum.

Trends in summer total ice (all ice types) (left) and multi-year ice (MYI, right) area from 1968 to 2016. Summer is defined as June 25 to October 15 for the Beaufort Sea, CAA, and Baffin Bay regions, and from June 18 to November 19 for Hudson Bay, Hudson Strait, Davis Strait, and Labrador Sea, consistent with Tivy et al. (2011a) and Derksen et al. (2012). Only trends significant at the 5% level (there is only a 5% possibility that the trend is due to chance) are shown.

Time series of summer total sea ice area for the (a) Beaufort Sea, (b) Canadian Arctic Archipelago (CAA), (c) Baffin Bay, and (d) Hudson Bay regions from 1968 to 2016.

(a)Time series of September Arctic sea ice extent (SIE) simulations that include the human-induced component (red) and simulations that include only natural factors (blue), shown as anomalies. Time series from 50 realizations of the Canadian Earth System Model (CanESM2) are shown, with the mean shown in bold. The time series of observations from the National Snow and Ice Data Center is shown in black. The horizontal dashed line indicates the record-low 2012 SIE. (b) Probability distributions for values from each set of simulations with (red) and without (blue) the human-induced component. Shading represents the uncertainty in the estimated distributions and the vertical dashed line indicates the record-low 2012 SIE.

(a) Map of average January–March sea ice area trends for subregions of the east coast and (b) time series of average January–March sea ice area trends for the entire region, 1969–2016.

Probability of sea ice–free conditions by 2050 under a high emission scenario (RCP8.5) from the Coupled Model Intercomparison Project (CMIP5) multi-model mean using a definition of ice-free conditions of 5% (left) and 30% (right) sea ice area.

Approximate area (shaded in white) of the last sea ice area in the Arctic during the summer months.

Map shows location of monitoring sites in the Canadian Arctic Archipelago and the Western Cordillera (image courtesy of Google Earth). Graphs show change in cumulative thickness of reference glaciers in the Canadian high Arctic (top left) and Western Cordillera (bottom left) since the early 1960s. Note the difference in y-axis scale between graphs.

Laurentian Great Lakes annual maximum ice cover (%) (1973–2018). Red dashed line indicates the long-term average.

Number of days earlier (negative numbers) or later (positive numbers) of (a) melt onset, (b) summer ice minimum, and (c) date that water is clear of ice for selected lakes in the central and eastern Canadian high Arctic from 1997 to 2011. Number of days’ change is reported relative to the 1997–2011 mean date (from remote sensing observations). Lakes in polar-oasis (relatively high annual precipitation) environments are shown as blue bars and lakes in polar-desert environments (relatively low annual precipitation) are shown as black bars. The red dashed line indicates the 1997–2011 mean change.

Change in mean date (number of days) of (a) freeze-up and (b) breakup between the current (1961–1990) and future (2041–2070) climatic periods for a hypothetical lake of 20 m depth. Note that all changes are in the positive direction (later ice freeze-up and earlier ice breakup). Simulations performed with the Canadian Regional Climate Model (CRCM4.2) using the SRES A2 emission scenario.

In the water cycle, water that evaporates from oceans is transported over land, where it falls as precipitation. It then either moves back to the atmosphere through evapotranspiration, is stored as ice or snow, or makes its way to rivers/streams (via various pathways), where it eventually flows back to the ocean.

Canada’s Reference Hydrometric Basin Network (RHBN), a subset of stations that have experienced little or no flow alteration and have thus widely been used for streamflow-related studies. This assessment relies on literature that incorporated primarily stations from the RHBN.

Summary of trends in one-day maximum flow in Canada using stations on unregulated streams from the Reference Hydrometric Basin Network (see Box 6.1). Significant trends denote that there is only a 5% possibility that such changes are due to chance.

Summary of trends in one-day minimum flow in Canada using stations on unregulated streams from the Reference Hydrometric Basin Network (see Box 6.1). Significant trends denote that there is only a 10% possibility that such changes are due to chance.

Summary of projected future changes to annual streamflow across Canada for the mid- to late 21st century based on various emission scenarios.

Trends in spring freshet timing (in days per decade with magnitude proportional to the size of the triangle) for 49 stations in unregulated streams from the Reference Hydrometric Basin Network (RHBN; see Box 6.1). Downward-pointing triangles represent earlier freshets and upward-pointing triangles represent later freshets. Green triangles indicate the trend is not significant. Significant trends denote that there is only a 5% possibility that such changes are due to chance. Data lengths range from 30 to 100 years.

Long-term mean amounts of daily runoff for (a) Fishtrap Creek near McLure, British Columbia (nival), (b) Lillooet River near Pemberton, British Columbia (glacial), (c) San Juan River near Port Renfrew, British Columbia (pluvial), and (d) southwest Miramichi River at Blackville, New Brunswick (mixed). All data are for the 1981–2000 period.

Locations of nival (snowmelt-dominated), pluvial (rainfall-dominated), and mixed streamflow regimes across Canada based on a subset of Reference Hydrometric Basin Network stations for the 1963–2012 period. Glacial regimes were not identified in this analysis.

Time series of mean over-lake precipitation, evaporation, and river runoff (measured as the effect on lake level) for the 1950–2016 period for (a) Lake Superior, (b) Lakes Michigan/Huron, (c) Lake Erie, and (d) Lake Ontario. (e) Time series of net basin supplies (NBS) for the 1950–2016 period for Lakes Superior, Michigan/Huron, Erie, and Ontario. Red lines and text represent linear trends. *Significant trends (there is only a 5% possibility that such changes are due to chance). Lakes Michigan and Huron are connected by the Straits of Mackinac and thus have the same water level. They are therefore considered as one lake.

Relative water-level changes for 10 representative closed-basin lakes across the southern Canadian Prairies for their period of record. Dashed lines connecting separated data points are not representative of measured water levels between the points. “D” indicates that the lake was dry at the time of measurement.

Number of ponds during May in the Canadian Prairies. Vertical bars show 90% confidence intervals.

Annual Palmer Drought Severity Index (PDSI) values from 1900 to 2007 for (a) Kamloops, British Columbia, (b) Saskatoon, Saskatchewan, (c) Sherbrooke, Quebec, and (d) Yarmouth, Nova Scotia. Solid lines represent 10-year running means. Positive values indicate wetter conditions, negative values indicate drier conditions.

Changes in mean annual Standardized Precipitation Evapotranspiration Index (SPEI) (left) and summer (June–August) SPEI (right) between the baseline (1971–2000) and 2041–2070 (top) and between baseline and 2071–2100 (bottom) for western Canadian watersheds. SPEI is determined from temperature and precipitation output from an ensemble of six CMIP5 GCMs under a high emission (RCP8.5) scenario. Positive values indicate wetter conditions, negative values indicate drier conditions.

Derived groundwater storage (GWS) measured in water thickness equivalent over the land areas of the Great Lakes Basin using the Center for Space Research (CSR) release 04 (RL04) (top) and GeoForschungsZentrum (GFZ) release 04 (RL04) (bottom) Gravity Recovery and Climate Experiment (GRACE) models. Each model incorporates three soil moisture, snow, and lake (SMSL) water storage fields that have different land-surface models.

Average groundwater storage (GWS) trends in Alberta using the release 05 monthly GRACE gravity model for the period April 2002 to October 2014 (left). The average is determined using four land-surface models from the Global Land Data Assimilation System: Mosaic (MOS), Noah, Variable Infiltration Capacity (VIC), and Community Land Model (CLM). Time series averaged over the entire province for each model (as well as the average of all four models [AVG]), and the linear trend are provided on the right. Twelve mean monthly GWS variation maps were generated from the 139 monthly GWS variation grids to characterize the annual GWS variations.

Trends for annual mean groundwater levels for 30-year (1976–2005, top) and 40-year (1966–2005, bottom) series. b represents the magnitude of the trend in metres per year. Significant trends denote that there is only a 10% possibility that such changes are due to chance.

Annual precipitation and average standardized groundwater levels in 24 monitoring wells in the Winnipeg, Manitoba, area. The upper graph shows actual values, while the lower graph provides values with precipitation shifted later by 2.2 years (as denoted by the Δτ in the upper graph).

Fall (September–November) average sea surface temperature (1985–2013) in the oceans surrounding Canada, based on advanced very-high-resolution radiometer satellite infrared imagery. The lines (both black and white) with arrowheads represent the general direction of upper-ocean currents. Ice-covered marine areas are coloured white.

Map showing locations of British Columbia Shore Station Oceanographic Program sites on the east (Entrance Island) and west (Amphitrite Point and Kains Island) coasts of Vancouver Island. Offshore ocean temperature, salinity and other observations are collected by the DFO Line P monitoring program extending out to Station P, which is the former location of the Ocean Weather Station Papa. The 200 m and 1000 m depth contours are indicated by the light and dark blue lines.

Coastal temperature time series collected at DFO monitoring sites on the east (Entrance Island, positive trend 0.15°C per decade, significant at 1% level [there is only a 1% possibility that such changes are due to chance]) and west (Amphitrite Point and Kains Island, positive trend 0.08°C per decade, significant at 1% level) coasts of Vancouver Island. Offshore ocean temperature at Station P is presented for the upper ocean (10–50 m, positive trend 0.14°C per decade, significant at 1% level) and the depth range of the permanent thermocline (layer in which temperature decreases strongly with depth; 100–150 m, positive trend 0.07°C per decade, significant at 5% level).

Map identifying areas of the Northwest Atlantic Ocean in which temperature and salinity time series are presented in this report. These areas include the Labrador Sea, Newfoundland Shelf, Scotian Shelf, Gulf of St. Lawrence, and Bay of Fundy. Ocean observations are collected by DFO Atlantic zone monitoring programs. The 200 m and 1000 m depth contours are indicated by the light and dark blue lines.

Ocean temperature time series for the surface and at depths of 200 and 300 m in the Gulf of St. Lawrence collected by DFO monitoring programs. Sea surface temperature (May to November average, ice-free period) from advanced very-high-resolution radiometer satellite observations (1985–2017, positive trend of 0.46°C per decade, significant at 1% level). Temperature from in situ observations at depths of 200 m (1915–2017, positive trend of 0.25°C per decade, significant at 1% level) and 300 m (1915–2017, positive trend of 0.23°C per decade, significant at 1% level) indicate warming in the deep Gulf of St. Lawrence over the past half-century.

Ocean temperature time series in the Scotian Shelf and one for the Bay of Fundy collected by DFO monitoring programs. Long-term increases are observed from in situ sea surface temperature (0 m, 1947–2016, positive trend of 0.15°C per decade, significant at 1% level) and for the deeper layer (250 m, 1947–2016, positive trend of 0.36°C per decade, significant at 1% level) of the Emerald Basin region of the Scotian Shelf. Depth-averaged ocean temperature (0–90 m) from the Prince 5 station in the Bay of Fundy (1924–2016, positive trend of 0.16°C per decade, significant at 1% level) indicates a similar long-term warming trend.

Ocean temperature time series in the Newfoundland Shelf and Labrador Sea collected by DFO monitoring programs. Sea surface temperature (0 m) on the Newfoundland Shelf at AZMP Station 27 near St. John’s (1950–2016, positive trend of 0.13°C per decade, significant at 1% level [there is only a 1% possibility that the trend is due to chance]) and depth-averaged ocean temperature (0–175 m) from that site (1950–2016, non-significant positive trend of 0.02°C per decade). Upper-ocean temperature (20–150 m) of the central Labrador Sea basin (OWS Bravo) does not demonstrate long-term warming (1948–2016, non-significant positive trend of 0.03°C per decade).

Fifth phase of the Coupled Model Intercomparison Project (CMIP5) ensemble mean sea surface temperature (SST) for the period of 1986–2005 (top row) for February (a) and August (b). Change in the mean SST for mid-century (2046–2065) relative to 1986–2005 for February (c) and August (d) for the high emission scenario (RCP8.5). Standard deviation in the SST change for mid-century relative to 1986–2005 for February (e) and August (f). In general, the standard deviation is small, indicating agreement among models, except for northern Baffin Bay and the regions south of Nova Scotia, Newfoundland, and Greenland; this can be attributed to the difficulty in modeling the ocean dynamics of these regions.

Annual mean salinity in the Pacific Ocean off British Columbia at same sites as the mean temperature in Figure 7.2. Long-term trends in these times series are small but statistically different from zero for the Station P (10–50 m) near-surface layer (1956–2017, declining trend of 0.015 per decade, significant at 5% level, (there is only a 5% possibility that the trend is due to chance]) and Amphitrite and Kains Islands (1935–2017, declining trend of 0.043 per decade, significant at 5% level). Interannual and decadal variability is large at Entrance Island (east Vancouver Island) relative to the sites on the west coast of Vancouver Island and at Station P. Long-term trends are not statistically different from zero at Entrance Island (1937–2017, increasing trend of 0.038 per decade) nor at Station P (100–150 m) deep layer (1956–2017, increasing trend of 0.013 per decade).

Annual mean salinity at representative sites from five different areas off Atlantic Canada, from Fisheries and Oceans Canada (DFO) monitoring programs. The Gulf of St. Lawrence (300 m depth) long-term trend is significantly positive (1915–2016, trend 0.019 per decade, significant at 1% level), in contrast to the other sites, which all have negative trends. The decreasing trend on the Newfoundland Shelf (Station 27, 0–175 m, 1950–2016, declining trend of 0.013 per decade, significant at 5% level) is statistically different from zero. The remaining sites do not have trends that are statistically different from zero (Labrador Sea, 20–150 m, 1928–2012, declining trend of 0.005 per decade; Scotian Shelf (Emerald Basin), 1951–2016, declining trend of 0.022 per decade; Bay of Fundy, 0–90 m, 1924–2016, declining trend of 0.009 per decade).

Stratification index (density difference from the ocean surface [0 m] to the depth of-50 m) is expressed as a mean annual anomaly (departure from normal) for the period 1948–2017. The time series for the Scotian Shelf is derived from data collected from several areas across the shelf, which are combined to provide one annual anomaly estimate. The time series for the Newfoundland Shelf is based on data collected at the AZMP Station 27. The long-term trend is significantly positive for both the Scotian Shelf (1948–2017, positive trend 0.0015 (kg/m3) per decade, significant at 1% level) and the Newfoundland Shelf (1948–2017, positive trend 0.00074 (kg/m3) per decade, significant at 1% level).

Fifth phase of the Coupled Model Intercomparison Project (CMIP5) ensemble mean sea surface salinity (SSS) for the period 1986–2005 (top row) for February (a) and August (b). Change in the mean SSS for mid-century (2046–2065) relative to 1986–2005 for February (c) and August (d) for a high emission scenario (RCP8.5). Standard deviation in the SSS change for mid-century relative to 1986–2005 for February (e) and August (f). Panels (c) and (d) show a general freshening of the sea surface in the Northeast Pacific and in the Northwest Atlantic north of 40° north latitude (decrease generally less than 1). In the North Atlantic subtropical gyre, the projection indicates an increase in salinity (increase generally less than 1). In the Northeast Pacific, the standard deviation is small, indicating agreement among models. In many areas of the Arctic and Northwest Atlantic Oceans, the large standard deviation indicates larger discrepancies between model projections in these areas, where sea ice and complex ocean dynamics are important processes that are difficult to simulate.

Rates of land uplift and subsidence determined from Global Positioning System (GPS)-derived data (in millimetres per year).

The water-level records (monthly values, with tides removed) of nine tide gauges distributed around Canada. The records show differing linear trends from one location to another, primarily indicating different amounts of vertical land motion arising from glacial isostatic adjustment and other factors. Superposed on this long-term change is substantial variability from year to year, indicating the changing nature of the oceans and the influence of climate cycles and other processes. For the west coast, the 1997/98 El Niño–Southern Oscillation event (ENSO, indicated by arrows) was a time of high water levels during the winter months. Individual tide gauge records are vertically offset for display purposes.

Projections of global average (mean) sea-level rise relative to 1986–2005 for low (RCP2.6) and high (RCP8.5) emission scenarios from IPCC AR5 (Church et al., 2013). Also shown is an enhanced scenario reflecting greater amounts of ice discharged from Antarctica and contributing to global sea-level rise (see Table 7.1). The lines indicate the median projection, and the shading indicates the assessed range (5th–95th percentile, or 90% uncertainty range). The projected global mean sea-level rise over 2081–2100 (relative to 1986-2005) is given on the right for these scenarios and for a medium emission scenario (RCP4.5). Lines and shading are the same as in the main graph.

Projected relative sea-level changes shown at 2100 for the median of a high emission scenario (RCP8.5) at 69 coastal locations in Canada and the northern United States. Values range from a sea-level fall of 84 cm to a sea-level rise of 93 cm and are relative to the average conditions in the 1986–2005 period. For comparison, the projected median global sea-level change at 2100 for the high emission scenario is 74 cm.

Projected relative sea-level change based on global sea-level projections from Church et al. (2013), and vertical (V) crustal motion (uplift rate, given to nearest 0.5 mm per year) derived from Global Positioning System (GPS) observations indicated in each panel for (a) Halifax, (b) Vancouver, (c) Nain, and (d) La Grande 1 (James et al., 2014, 2015; Lemmen et al., 2016). Projections are given through the current century for low emission (RCP2.6), medium emission (RCP4.5), and high emission (RCP8.5) scenarios. The projected value by 2100 is also given for the enhanced scenario (RCP8.5 plus 65 cm reflecting Antarctic Ice Sheet (AIS) reduction; green triangle). Rectangles show the 90% uncertainty range (5th–95th percentile) of the average projection over the 2081–2100 period and also include the medium (RCP6.0) emission scenario; the dashed red line shows the 95th percentile value for the high emission scenario.

A storm surge results from an atmospheric low-pressure system and strong winds blowing onshore during large storms. Strong low-pressure systems raise the surface of the ocean due to their reduced atmospheric pressure. Winds that blow onshore cause water to flow toward the coastline, resulting in wind set-up (rise in water level from wind stresses on the surface of the water). As waves enter shallow coastal water and break, wave set-up (rise in water level due to breaking waves) further raises the water level. Waves rushing up a beach or structure generate additional wave run-up. All of these factors contribute to high water levels that are superimposed on the predicted tide. MSL datum = mean sea-level datum.

Hourly water levels recorded at Halifax Harbour for 1920 to 2018, with 5% extremes shown in dark blue and the 90% mid-range in light blue. Mean sea level (thick blue line) exhibits short-term variability superposed on a long-term increase throughout the record duration. Flood levels at 2.3 m (red line) and 2.1 m (aqua line) show increasing numbers of extreme water-level events throughout the record duration, a consequence of the rise in mean sea level. The number of events at the lower 2.1 m flood level (596) is much higher than at the higher 2.3 m level (131).

The ocean carbon cycle is represented by fluxes (yellow arrows), which include the annual net transfer of carbon dioxide (CO2) between the atmosphere and ocean surface. The carbon inventory (rectangles) indicates that the deep ocean is a large storage reservoir and important to the Earth’s climate system.

pH (depth-averaged) time series over the Scotian Shelf (1933–2014, declining trend of 0.026 per decade; 1995–2014, declining trend of 0.044 per decade); near-bottom estimate (approximately 300 m) of pH in the Gulf of St. Lawrence (1935–2007, declining trend of 0.021 per decade; 1990-2007, declining trend of 0.026 per decade); and pH from the central Labrador Sea in the annually ventilated layer (150–300 m) (1996–2016, declining trend of 0.029 per decade). Estimates of pH before the 1990s have a high level of uncertainty because of the quality of the measurements and should be interpreted with caution. Therefore, no assessment of statistical confidence is provided for the observed trends.

Dissolved oxygen (DO) status and trend in various regions. Most of the trends are based on short time series, which could be strongly influenced by natural (e.g., decadal) variability. However, long-term time series do exist for the Northeast Pacific (Station P) and in the Gulf of St. Lawrence, and these show statistically significant declining trends in DO. The 200 m and 1000 m depth contours are indicated by the light and dark blue lines.

Dissolved oxygen concentration at 300 m depth in the Lower St. Lawrence Estuary (1932–2016, declining trend of 0.89 µmol/kg per decade, significant at 1% level); depth-averaged dissolved oxygen concentration in the Labrador Sea (150–400 m, 1990–2011, declining trend of 0.75 µmol/kg per decade, significant at 1% level); Station P dissolved oxygen concentration at 150 m depth (1956–2017, declining trend 0.61 µmol/kg per decade, significant at 1% level [there is only a 1% possibility that such changes are due to chance]) and at 400 m depth (1957–2017, declining trend 0.19 µmol/kg per decade, significant at 1% level).

Map of Canada showing selected places mentioned in the text. PEI is Prince Edward Island, VI is Vancouver Island, SoG is Strait of Georgia, MD is Mackenzie Delta, S is Lake Superior, H is Lake Huron, M is Lake Michigan, E is Lake Erie, and O is Lake Ontario.