DYNAMIC COASTS in a CHANGING CLIMATE Lead Authors: David E
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CHAPTER 2: DYNAMIC COASTS IN A CHANGING CLIMATE Lead Authors: David E. Atkinson (University of Victoria), Donald L. Forbes (Natural Resources Canada) and Thomas S. James (Natural Resources Canada) Contributing Authors: Nicole J. Couture (Natural Resources Canada) and Gavin K. Manson (Natural Resources Canada) Recommended Citation: Atkinson, D.E., Forbes, D.L. and James, T.S. (2016): Dynamic coasts in a changing climate; in Canada’s Marine Coasts in a Changing Climate, (ed.) D.S. Lemmen, F.J. Warren, T.S. James and C.S.L. Mercer Clarke; Government of Canada, Ottawa, ON, p. 27-68. Chapter 2 | DYNAMIC COASTS IN A CHANGING CLIMATE 27 TABLE OF CONTENTS 1 INTRODUCTION 29 4.3 PROJECTIONS OF SEA-LEVEL CHANGE IN CANADA 51 2 COASTAL VARIABILITY 29 4.3.1 PROJECTIONS OF RELATIVE SEA-LEVEL CHANGE 51 2.1 GEOLOGICAL SETTING 30 4.3.2 EXTREME WATER LEVELS 52 2.2 COASTAL PROCESSES 33 4.3.3 SEA-LEVEL PROJECTIONS 2.2.1 EROSION AND SHORELINE RETREAT 35 BEYOND 2100 54 2.2.2 CONTROLS ON RATES OF COASTAL CHANGE 36 5 COASTAL RESPONSE TO SEA-LEVEL RISE 3 CHANGING CLIMATE 38 AND CLIMATE CHANGE 54 3.1 DRIVERS OF CHANGE 38 5.1 PHYSICAL RESPONSE 54 3.2 CLIMATE VARIABILITY AND CHANGE 40 5.2 ECOLOGICAL RESPONSE 57 3.3 CLIMATE DETERMINANTS 41 5.2.1 COASTAL SQUEEZE 57 3.4 TRENDS AND PROJECTIONS 42 5.2.2 COASTAL DUNES 57 3.4.1 TRENDS 42 5.2.3 COASTAL WETLANDS, TIDAL FLATS AND SHALLOW COASTAL WATERS 59 3.4.2 PROJECTIONS 43 3.5 STORMS AND SEA ICE 43 5.3 VISUALIZATION OF COASTAL FLOODING 60 3.5.1 STORMS 43 3.5.2 SEA ICE 44 6 SUMMARY AND SYNTHESIS 60 3.5.3 CHANGES IN STORM ACTIVITY 45 7 REFERENCES 62 4 CHANGING SEA LEVEL 46 4.1 HISTORICAL SEA-LEVEL CHANGE 46 4.2 FUTURE SEA-LEVEL CHANGE 48 4.2.1 GLOBAL SEA-LEVEL RISE 48 4.2.2 VERTICAL LAND MOTION 50 4.2.3 EFFECTS OF PRESENT-DAY ICE-MASS CHANGE 51 4.2.4 REGIONAL OCEANOGRAPHIC EFFECTS 51 28 CANADA’S MARINE COASTS in a CHANGING CLIMATE 1 INTRODUCTION 2 COASTAL VARIABILITY This chapter focuses on the dynamic nature of Canada’s Canada has not only the world’s longest coastline (about marine coast and the environmental drivers of coastal 243 000 km; Taylor et al., 2014), but arguably one of the most change in a changing climate. An understanding of how diverse. All provinces and territories, except Alberta and changing climate affects coastal stability, and the nature of Saskatchewan, have marine coasts. These range from the coastal response, provides a basis for assessing potential high- energy rock headlands of southern Newfoundland changes in coastal hazards and the implications for human to very low energy, ice-locked, sedimentary coasts in the communities and infrastructure. Whereas the effects of northwestern Canadian Arctic Archipelago. They include climate change on sea level are widely understood (IPCC, deeply indented fiord topography, cliffs cut in bedrock 2013), the secondary effects of sea-level change on coasts or glacial/proglacial deposits, beaches, spits and barrier continue to challenge our understanding and management islands, dunes, salt marshes and tidal flats, ice-rich permafrost practices (Davidson-Arnott, 2005; FitzGerald et al., 2008; coasts, and large deltas such as those at the mouth of the Wolinsky, 2009; Wolinsky and Murray, 2009; Wong et al., Fraser River in British Columbia and the Mackenzie River in 2014; Woodroffe et al., 2014). Other aspects of climate the western Arctic. Canada’s coasts are affected by tides that change have significant impact on coasts, including changes range from negligible to the world’s highest (in the Bay of in storminess, storm surge and wave climate; changing Fundy and Ungava Bay). Exposure to wave energy ranges from seawater properties, including temperature and pH; and very low, in well protected settings, to very high, in settings the changing nature, duration and dynamics of sea ice. with full Atlantic or Pacific ocean exposure. Variability in coastal The chapter begins with an overview of the diversity and geomorphology and processes is high within and between dynamic nature of Canada’s marine coasts (Figure 1). Following all regions considered in this report (see Chapters 4–6). this is an overview of changing coastal climates, including past Sea-level changes in Canada are driven only in part by and projected future changes in temperature, precipitation, trends in global mean sea level. Locally, significant variation storminess and associated weather events that drive coastal from the global mean trend can arise from several factors. change. It then provides a summary of past trends in sea level Among the most important of these is vertical crustal motion, and the latest projections of future changes in mean sea level which results in trends in relative sea level varying widely in Canada, and concludes with the implications of a changing across Canada, from rapid fall in parts of the central Arctic climate, including changes in mean and extreme water levels, to accelerating rise in the Maritimes. This and other factors for the physical state and ecological integrity of the coast. influencing local sea-level change are discussed in detail Although this chapter focuses on the physical environment in Section 4 of this chapter. of coasts, the effects of climate change are much broader The importance of sea ice also varies significantly along in scope, touching ecosystem sustainability, renewable Canada’s marine coasts. In the Arctic, sea ice effectively resources, food security, health and well-being, energy, shuts down or severely constrains coastal dynamics for much economic prosperity, cultural integrity and other facets of of the year, and limits open-water fetch in the summer. these social-ecological systems. These topics are discussed Most parts of the east coast are exposed to sea ice on an in subsequent chapters of this report (see Chapters 3–6). annual basis, with effects that range from substantial to negligible. On the west coast, thin ice occurs only rarely in protected waters. In all areas where sea ice occurs, it can play an important role in sediment transport, shore-zone morphology and ice-related hazards (Forbes and Taylor, 1994). Climate warming has already affected mean dates of breakup and freeze-up of sea ice and the length of the open-water season (Stammerjohn et al., 2012; Stroeve et al., 2012), with important implications for coastal exposure to storm waves and surges (Vermaire et al., 2013). Reduction of sea ice is an important concern for ice- dependent ecological and human systems (e.g., Gaston et al., 2012; Laidre et al., 2012; Stirling and Derocher, 2012). FIGURE 1: Canada’s marine coasts, broadly delineating the three regions discussed in this report. Chapter 2 | DYNAMIC COASTS IN A CHANGING CLIMATE 29 Storm climatology (e.g., storm characteristics, severity, wash and slumping; Manson, 2002; Forbes, 2011). Active seasonal frequency, track mode and variance) varies between glaciation in the Coast Mountains, BC, St. Elias Mountains, Atlantic, Arctic and Pacific coasts (e.g., Wang et al., 2006), and YT, and the eastern Arctic continues to feed outwash sedi- around the Arctic basin (Atkinson, 2005). The Atlantic coast ments to the ocean (Forbes, 2011). The extent of floating ice experiences the full range of extra-tropical and tropical shelves along the north coast of Ellesmere Island, NU, has cyclonic storm systems, as well as rapidly evolving ‘tropical decreased precipitously in recent years, but some portion transition events’ (storms in the process of evolving from of the ice front remains (see Chapter 5; Mueller et al., 2003; tropical to extra-tropical cyclones). All of these storm types Copland et al., 2007). have implications for coastal stability and hazards (Forbes The effects of the last continental glaciation are also et al., 2004; Parkes et al., 2006). The Pacific coast experiences paramount in determining the direction and rate of sea-level large, mature extra-tropical storm systems that often stall change in Canada, which is a primary control on coastal when encountering the Coast Mountains, creating the evolution. In regions such as Hudson Bay, where the greatest potential for prolonged impact. Northern Canada experi- amount of isostatic depression of the Earth’s crust by conti- ences storms moving into the region, rather than forming nental ice sheets occurred during the Last Glacial Maximum in place. The most prominent track is from the southeast (20–25 thousand years ago), glacial isostatic uplift is ongoing, (Labrador Sea northward to Baffin Island, NU), with a major local sea level is falling and the coast is emerging. Where secondary track coming from the west through the Beaufort coastal emergence has been ongoing for thousands of years, Sea (Maxwell, 1981, 1982). abandoned shorelines are delineated by successions of uplifted beaches (Figure 3; St-Hilaire-Gravel et al., 2010) 2.1 GEOLOGICAL SETTING and coastal communities in these regions face progressive shallowing of their marine approaches (Forbes et al., 2014a), The legacy of past glaciation is apparent almost which can be as problematic as local sea-level rise. everywhere in Canada, influencing the evolution and In areas marginal to the former continental ice sheet, the morphology of the coast (Forbes, 2011) and differentiating postglacial response is regional subsidence, such that former Canada’s coast from much of the coastline of the United shorelines are now submerged below sea level (Figure 4; Shaw States mainland to the south. Large fiords, the product of et al., 2002). These submergent coasts can be recognized by glacial erosion, dominate the coasts of British Columbia, bays and estuaries created through the gradual inundation of parts of Newfoundland and Labrador, and the eastern islands river valleys, and by spits and barrier beaches formed across of the Canadian Arctic Archipelago (Figure 2).