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An Overview of Canada’s Changing Climate Bush, E.J., J.W. Loder, T.S. James, L.D. Mortsch and S.J. Cohen. In Canada in a Changing Climate: Sector Perspectives on Impacts and Adaptation. 2014 Contents of the 2014 update report FULL REPORT Synthesis 1. Introduction 2. An Overview of Canada’s Changing Climate (EC, DFO, NRCan) 3. Natural Resources 4. Food Production 5. Industry 6. Biodiversity and Protected Areas 7. Human Health 8. Water and Transportation Infrastructure 9. Adaptation: Linking Research and Practice 2 1 Contents of Chapter Two 1. Introduction 2. Changes in Air Temperature and Precipitation 3. Changes to the Cryosphere • Permafrost • Snow cover • Glaciers • Freshwater Ice and Sea Ice 4. Changes to Freshwater Resources 5. Changes in Ocean Climate • Temperature • Salinity and density stratification • Hypoxia and acidity • Sea level change 6. Summary Chapter discusses both observed and projected changes for each component 3 Chapter objectives • Bring climate information of broad interest to Canadians together in one place – Large suite of indicators for changes in temperature, precipitation, freshwater, snow, ice and permafrost, ocean climate and sea level – Focus is on changes at the national scale; regional variability discussed • Update results from the 2008 report – Focus on literature from the past few years – Provide updated climate change projections from 2008 report • Increase awareness about the scope and magnitude of changes that are occurring already across Canada and those that are expected to occur over the coming century and beyond The chapter draws heavily on long-term monitoring programs of Environment Canada, Fisheries and Oceans Canada and Natural Resources Canada. 4 2 Chapter scope: the climate system IPCC, 2007 5 Assessing climate change and human influence becomes more challenging at regional scales Detection and attribution of change from analyses of long observational records, understanding of causes and use of models Sparse Observations + Large Natural Variability (e.g. Decadal-Scale) Challenges in Separating Anthropogenic and Natural Change Projections of future change, from recent changes, coupled climate model simulations, and knowledge of Earth’s climate system Uncertainty in climate system response + Model limitations Need ensemble projections from many models Challenges in Downscaling to regional scale projections 6 3 Global warming is unequivocal and greenhouse gases are the dominant cause • Global temperature has increased about 0.85°C since 1880 • Each of the last three decades has been warmer than all preceding decades since 1850 • Observed warming has been primarily due to human emissions of greenhouse gases 1oC 2000s 1990s 1980s (IPCC, 2013) 7 Warming in Canada has been about twice the global average Annual mean temperature anomalies (°C) relative to 1961-1990 Trend in annual mean surface temperature, between 1950-2010 of 1.5°C EnvCan, 2011 • Nighttime min temperatures rising faster than daytime max temperatures • Increasing number of warm summer days and decreasing number of cold 8 winter nights 4 Warming has been widespread across Canada Trends in seasonal mean temperature, 1950-2010 Winter Warming observed in all seasons Summer Most pronounced in winter and spring, and weakest in the fall. Fall Spring Largest in west (winter and spring) and north (fall) 9 Vincent et al., 2012 Precipitation has been increasing across Canada as a whole; less snowfall in winter in southern Canada 1950-2010 • Increase in total annual precipitation of ~16% • Increasing annual rainfall • Variability across Canada • Snowfall shifting to rainfall in southern Canada in winter EnvCan, 2011 Rainfall Snowfall Annual rainfall and snowfall trends, 1950-2009 (mm/yr) 10 Mekis and Vincent, 2011 5 There have been significant changes in heavy rainfalls in some areas • • • No consistent pattern of change for Canada Trends in extreme precipitation, 1950-2010 Observed changes are consistent with those for North America and Northern Hemisphere land areas Global analyses indicate trends towards more severe drought in southern and western Canada since 1950 Vincent and Mekis, 2006, updated 11 This century, Canada could look quite different than the Canada we are currently adapted to Low emissions scenario WINTER SUMMER Air Temperature SUMMER High emissions scenario WINTER Projected seasonal changes in surface air temperature (°C), 2080s Precipitation Low emissions scenario SUMMER WINTER High emissions scenario SUMMER WINTER Projected seasonal changes in precipitation (%), 2080s Canadian Climate Change Scenarios Network: www.cccsn.ec.gc.ca/ 12 6 Some types of extreme weather will increase as the climate continues to warm; others will decrease Projected changes in temperature extremes Extremes in daily temperature • • Increases in the frequency and magnitude of unusually warm days and nights Decreases in unusually cold days and nights Long duration events • Increase in the length, frequency and intensity of warm spells, heat waves over most land areas, including Canada Rare hot extremes • One-in-twenty year extreme hot day projected to become about a onein-five year event over most of Canada by mid-century Projected changes in precipitation extremes Heavy precipitation • More frequent heavy precipitation events are projected with an associated increased risk of flooding Rare precipitation events • Rare events projected to become about twice as frequent by midcentury over most of Canada 13 Snow cover is declining especially in Spring Observed - Earlier spring snow melt is driving the declining # days with snow cover in the second half of the snow season Projected - Widespread decreases in the duration of snow cover throughout the year 2080s vs 1980s 1950-2007 14 7 Summer sea ice cover is declining and getting thinner in Canadian waters Canadian Ice Service Digital Archive data, decadal changes over 1968-2010 • All ice trends include first year and multiyear ice • Rapid declines in summer ice cover are evident in Canadian sea ice regions • Largest declines of 17% per decade • Consistent with Arctic Ocean results, ice cover is getting thinner in some areas (less multi-year ice) • Canadian archipelago receives in-flow of multi-year ice from the Arctic Ocean • Ice conditions could remain difficult there into the future 15 % change per decade Derksen et al. 2012 Permafrost temperatures have increased in recent decades • Ground temperatures have increased in both warm discontinuous permafrost zones and colder areas Norman Wells Alert • Warming and thawing of permafrost will continue but thawing of cold permafrost could take many decades to centuries 16 Credit: Sharon Smith, NRCAN 8 Glaciers in both western Canada and the high Arctic are receding Changes in net mass balance indicate whether the glacier is gaining or losing ice Observed: • Significant declines in glacier mass are evident over the past several decades • Western glaciers are reaching record low extents 17 Credit: NRCAN, GSC Observed Changes to Freshwater Resources Trends in 1-day maximum (left) and minimum (right) river flow, 1970-2005. Ecosystem Status and Trends Report, 2010 • Watersheds strongly influenced by spring snowmelt (most of Canada except for the Pacific coast) can be expected to experience an earlier peak in maximum runoff in the spring • Depending on the amount of warming, this peak could occur several weeks earlier than present timing in a warmer climate 18 9 Projected changes in annual runoff Global models Regional studies (IPCC WGII, 2014) Fig. 23, Ch. 2 • Projected changes for the 2050s, from 44 • global model runs, based on ~2°C warming Pronounced increase in run-off in northern Canada, but smaller changes in southern Canada (with uncertainty in sign) • • Projected changes for the 2050s, from regional studies -/+ indicates both decreases and increases in southern Canada, and overall uncertainty 19 Ocean climate change around Canada Canada is bounded by three oceans with a complex coastline and many coastal seas. Arctic NW Atlantic NE Pacific DFO Long-term Monitoring Sites Ocean variability is heavily influenced by the atmosphere, but the oceans also have internal variability and large influences on the atmosphere on both global and regional scales. Long-term observational records are more limited than for the atmosphere, so detection of climate change is more difficult 20 10 Observed Changes in Global Ocean Climate (IPCC AR4, 2007) In mid-high latitudes Surface warming and freshening reduced surface water density increased stratification reduced oxygen and nutrient supply Increased CO2 uptake decreased pH / increased acidity shallower CaCO3 saturation depths impacts on shell formation 21 Observed Changes in Global Ocean Climate (IPCC AR4, 2007) In mid-high latitudes Surface warming and freshening reduced surface water density increased stratification reduced oxygen and nutrient supply Increased CO2 uptake decreased pH / increased acidity shallower CaCO3 saturation depths impacts on shell formation 22 11 Temperature, salinity and subsurface oxygen are changing off Canada’s Pacific coast Ocean Temperature Long-term warming trends of ~0.1oC per decade in near-surface waters 2oC Weak freshening trends at some locations Dissolved Oxygen Strong natural decadalscale variability (e.g. El Niño) (DFO Monitoring Programs) 100 μmole/kg Decreasing subsurface oxygen in NE Pacific and along BC shelf => Ocean hypoxia a serious issue for some marine organisms Hypoxic 1920 2010 23 Temperature, salinity and subsurface oxygen are also changing off Canada’s Atlantic coast Long-term warming trends of ~0.1-0.2oC per decade in the Gulf of St. Lawrence and Bay of Fundy Ocean Temperature Long-term surface freshening in the Bay of Fundy. 2oC Ocean Salinity (DFO Monitoring Programs) 1 1910 2010 Increasing salinity at depth in the Gulf of St. Lawrence due to competing influences from surface freshening and ocean circulation changes No net long-term changes in temperature and salinity off Newfoundland and Labrador due to strong natural multidecadal variability 24 12 Changes in Ocean Acidity Increasing CO2 in the atmosphere leads to increasing CO2 in the ocean • lowers pH leading to “ocean acidification” • pH has decreased by ~0.1 since the beginning of the industrial era Observational data off Canada, although sparse, indicate that acidification is generally occurring at rates near the global average but larger in some areas • e.g. at depth in the St. Lawrence Estuary Ocean acidification effects are more pronounced in the cold fresh waters of the Arctic where carbonate saturation depths are already shallow Ocean acidification has numerous adverse implications for marine ecosystems, including increased difficulty for some organisms to build calcareous shells. 25 Global mean sea level rose through the 20th century, and has risen faster in the past 2 decades 300 mm Global mean sea level increased by 21 cm from 1880 to 2012. Global sea-level rose at 1.7 ± 0.5 mm/yr in 20th century. For 1993-2003, global sea-level has risen at 3.1 ± 0.7 mm/yr and this trend continues to the present. 0 1870 2020 26 13 Relative sea level (RSL) rise along Canadian coastlines is strongly influenced by vertical land motion due to rebound from past glaciation Model simulation of vertical land motion due to Glacial Isostatic Adjustment (also known as “postglacial rebound”) Land rising in central parts of continent and sinking around edges Beaufort This contributes to RSL fall in some areas (e.g. Hudson Bay, north shore of Gulf of St. Lawrence) and to RSL rise in others (e.g. Beaufort, Maritimes) Maritimes (ICE-5G, Peltier 2004) Vertical land motion due to tectonics contributes to RSL along BC coast (not shown here). 27 Most Projections Indicate a Continuing Acceleration of Global Sea-level Rise through the 21st Century Shading: IPCC TAR. Vertical bars: IPCC 4th AR. Global sea level may rise by more than 1 metre by 2100. A rise of ten’s of centimetres is all but assured. Future relative sealevel change will continue to be influenced by vertical land motion. Global seal level will continue to rise beyond 2100, perhaps by many metres. 28 14 Extreme high water levels are expected to increase in frequency where mean sea-level is projected to rise • Rise in relative sea level will contribute to increased extreme (high) water levels, flooding, and coastal erosion in parts of Canada. • Reduced sea-ice cover is expected to contribute to extreme water levels and coastal erosion in some regions of Arctic and Atlantic Canada. • Increased storminess is also expected to contribute to increased extreme water levels and coastal erosion, but projections are equivocal about magnitude and location. 29 Future Changes in Ocean Climate Expect over 50-100 years: • Widespread warming, especially in surface waters • Decreasing extent and volume of sea ice • Surface freshening in most areas • Coastal sea level rise and increasing occurrence of coastal erosion and flooding in many areas • Increases in wave activity in areas with reduced sea ice • Widespread increasing ocean acidity and decreasing subsurface oxygen Important: - Seasonal and spatial variability - Natural decadal-scale variability may predominate for some variables in some areas over the next few decades - Limitations of models for quantitative projections with robust confidence for most variables 30 15 Assessment Synthesis key conclusion #1: Canada’s climate is changing, with observed changes in air temperature, precipitation, snow and ice cover and other indicators. Further changes are inevitable. OBSERVED TRENDS: Atmosphere / land surface • • Surface temperature in Canada has increased by 1.5°C since 1950, about twice global average. Cold extremes have decreased, hot extremes have increased, precipitation has increased overall and winter snowfall is shifting to rainfall in southern Canada; widespread reductions in the amount and duration of snow and ice cover. Oceans: • • Upper-ocean warming and reductions in subsurface oxygen off most of Pacific and Atlantic Canada, and increasing ocean acidity off all three Canadian coasts. Sea level is rising more quickly than the global average along Canadian coastal areas where the land is subsiding due to glacial rebound, while sea level has fallen in some other areas where glacial rebound or tectonics is causing the land to rise. FUTURE CHANGES: • • Continuation and exacerbation of many of the observed trends - warming, increased precipitation, reduced ice and snow cover, increasing ocean acidity and rising sea level. Regional and short term variability will persist, particularly for indicators such as surface freshwater availability. 31 16