Degrees of Change – Ecosystems
2.0 The NRTEE’s Degrees of Change diagram: Illustrating the Impacts of Climate Change in Canada
Ecosystems
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This category includes communities of biota — plants and animals — that live on land and in water, interacting with each other and their environment. Canada is rich in ecosystem diversity, with 15 distinct ecozones on land and five marine-based ones.[29] Ecosystems perform a range of services that we value greatly, whether we know it or not. They provide water, food, and fibre for our direct consumption or as inputs for industry. They regulate natural processes. The 1.2 million square kilometres of wetlands[30] covering about 14% of Canada’s land, for example, help absorb high-energy waves and control coastal erosion.[31] Our expansive forests — representing about 10% of the world’s forest cover — and soils absorb and store carbon dioxide, playing a key role in regulating the climate.[32] They are important for recreation and spiritual purposes. They support processes that sustain life, as we know it, such as nutrient cycling and photosynthesis.
A changing climate is already affecting Canada’s ecosystems.[33] Combined with pressures from economic development, including pollution, overuse, habitat fragmentation, and introduction of invasive species, future climate change has the potential to not only alter the quality and health of our ecosystems but also to set off physical processes that add to global climate warming. We include examples of these instances below (also see Box 2 on Climate Lags and Feedbacks).
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What we can expect
EFFECTS TO PLANTS, ANIMALS, AND FOOD WEBS FROM CHANGES IN CHEMISTRY AND TEMPERATURE OF OCEANS AND FRESHWATER SYSTEMS.
In addition to their role as heat sinks, oceans have 50 times the capacity of the atmosphere to store carbon, providing an important buffer to global climate warming.[34] Increasing levels of carbon in the atmosphere, however, are changing the surface chemistry of the oceans toward an environment that is more acidic.[35] Ocean acidification poses threats to marine life, including reducing the capacity of many organisms to form calcium carbonate shells.[36] In Canadian waters, plankton, pteropods, molluscs, and cold-water corals are particularly at risk,[37] some of which play key roles in the sustainability of marine food webs. One study estimates that by 2100, 70% of known cold-water stony coral ecosystems will no longer be able to maintain their calcified skeletal structures due to the impact of ocean acidification.[38] Waters off Nova Scotia and New Brunswick are currently home to at least 45 of the 500 cold-water coral occurring worldwide.[39]
Warmer temperatures affect the availability of oxygen in marine and freshwater columns. Globally, ocean surface temperatures have increased over the past 40 years,[40] contributing to the spread of “dead zones” or areas depleted in oxygen. In the Saanich Inlet on the coast of British Columbia, for example, the depth of waters depleted in oxygen is now 25 metres higher than 50 years ago, shrinking the habitat for many marine organisms and causing ripple effects on the viability of predators such as seabirds.[41]The ecology of the Great Lakes also stands to be affected by warmer surface temperatures. Projected warming of lake surfaces by 2100 would accelerate plants’ and animals’ use of dissolved oxygen, resulting in lower overall oxygen levels and limiting the habitat for various species of fish.[42]
SHIFTING GEOGRAPHIC DISTRIBUTION AND COMPOSITION OF ECOSYSTEMS.
A changing climate will alter the Canadian landscape and seascape. Ecosystems are expected to change in composition and to gradually move northward (and upslope on land, deeper in water), with some species gaining suitable habitat and others losing it.[43] This shift in habitat suitability has implications for the spread of invasive species. Warmer conditions, for example, are likely to prompt expansion of the introduced Asian shore crab, threatening soft-shell crabs and blue mussel fisheries.[44]
For forests, models forecast a northward expansion of boreal forest cover into what is currently tundra,[45] at the same time forecasting risks of significant loss of boreal forest, in particular at the southern edge of current boreal extent. One study estimates a one-in-three chance of losing 20% of boreal forest at a global temperature increase of 3.5°C over pre-industrial levels.[46] As the boreal forest cover moves north, it will replace tundra areas, with one study projecting 10% loss of tundra area by the end of the century.[47]
On land, the timing of several events in the life histories of plants and animals, like seasonal migrations, egg-laying, and blooming, depend on temperature. In a changing climate, the timing of these seasonal activities is shifting. For example, researchers have documented a 26-day shift in the onset of spring in Alberta over the past century, based on trends in the flowering dates of key perennial plants.[48]
Among other important consequences, shifts in vegetation cover and composition of ecosystems will have significant implications for current land-based parks and protected areas, some specifically established to protect certain ecological features and conserve current biodiversity levels.[49] Canada’s National Park system, for example, encompasses areas that are representative of Canada’s ecozones as we know them today.
CHANGING PATTERNS OF NATURAL DISTURBANCES.
Disturbances such as fires and insect outbreaks are important for natural reproduction and rejuvenation of forests like the boreal. However, climate change is likely to accelerate the intensity and frequency of fires and insect outbreaks, changing the forest landscape and releasing carbon stored in trees and soils as emissions into the atmosphere.[50] The average forest area burned from wildfires in Canada is already on the rise.[51] The average area burned per decade could increase by a factor of 3.5 to 5 by the last decade of this century.[52] The area burned in Canada is projected to increase about 75% to 100% by the end of this century at global temperatures 4°C and above.[53] This aggregate number masks a wide range of regional impacts: the average forest area burned in western wildfires could increase by 200% to 400% by the end of this century. In a warming world, insect attacks are likely to increase in frequency and intensity as established forest stands face stress from warmer, drier conditions, and as population dynamics of forest pests shift.[54]
| BOX 5: FOREST FIRES |
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Several severe fire seasons have occurred in the past decade, most notably the 2003 season in British Columbia., which cost the province $700 million in fire suppression costs. In the 1990s, the average area burned per fire in B.C. was about 125 hectares. In the 2000s, that average climbed to over 400 hectares. The 2004 summer in Yukon was the warmest on record and the area burned in that territory was more than twice the highest previous amount, which occurred in 1958. Pests and fire can have strong interactions — the dead and dying forests represent highly flammable conditions that could lead to very large areas burned, if hot and windy weather conditions prevail over a region. Sources: ArborVitae Environmental Services Ltd. & Dr. Gary Bull (2010). The Economic Implications of Climate Change on Non-Timber Values of Canada’s Forests, report commissioned by the National Round Table on the Environment and the Economy; estimates on average area burned in British Columbia use data from http://canadaforests.nrcan.gc.ca/statsprofile/forest/bc |
Changes in climate conditions, habitat, and food webs have implications for the viability of specific species of plants and animals. Here we highlight the killer whale and polar bear.[55] Killer whales are losing their traditional food sources as fish and mammalian species migrate northward.[56] Off the coast of British Columbia, reports of killer whales feeding on sea otters instead of sea lions and harbour seals have come in. Because of changes in fish migration patterns, sea lions and harbour seals have moved out of the killer whales’ range. The decline in abundance of Chinook salmon from the Fraser River is a major threat to resident killer whales.
Polar bears depend on sea ice as hunting platforms and for transportation; the duration and extent of sea ice influence the viability of polar bear populations. Some polar bear subpopulations are already under threat from changes in sea-ice conditions.[57] In Hudson Bay, local air temperatures have increased by 2 to 3°C over the last 50 years. This has led to earlier spring breakup of ice, affecting the success of the Western Hudson Bay polar bears.[58] A continued trend of warming and reduced access to sea ice poses significant extinction risk to this polar bear subpopulation by the end of the century.[59]
What we can do about it
On balance, scientists project losses in biodiversity in a changing climate, especially for ecosystems already under pressure from other causes. This is mainly because climate conditions are likely to change faster than ecosystems and species within them can adapt. Plants and animals naturally adjust to changes in their environment by changing behaviour, shifting timing of events in their life histories like reproduction and, in some cases, migrating to other suitable locations. Collectively, these adjustments represent changes to ecosystems and hence biodiversity, resulting in expansion and contraction of species’ ranges and ensembles of species over relatively long timeframes. For example, the shrinkage of glaciers increases the area of land for tundra ecosystems to occupy, but it could take over 300 years to achieve a dense tundra plant cover after the ice melts.[60]
Initiatives that enhance ecosystem resilience can help withstand the impacts of climate change (see Box 6). These include establishing or expanding networks of protected areas and migration corridors, and applying adaptive management and ecosystem-based approaches in economic activities like forestry and fisheries.[61] As ecosystems and species shift in response to climate change, national park management and boundaries will also need to adapt to ensure that the targeted ecosystems and species remain protected.[62]
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Footnotes
29 http://ecozones.ca/english/introduction.html
30 Wetlands include swamps, bogs, marshes, fens,and other areas where the soil is saturated either permanently or for part of the year (Statistics Canada 2010).
31 http://www.ec.gc.ca/default.asp?lang=En&n=540B1882-1 September 14, 2010.
32 Statistics are from http://canadaforests.nrcan.gc.ca/keyfacts. Carlson et al. (2010) describe the role of Canada’s forests and peatlands in regulating the global climate and provide recommendations to maintain and enhance the carbon storage potential of these ecosystems.
33 Lemmen et al. (2008).
34 Solomon et al. (2007).
35 Harley et al. (2006).
36 Brierley and Kingsford (2009); Denman (2008); Hoegh-Guldberg (2007).
37 Harley et al.( 2006), Herr & Galland (2009).
38 Herr & Galland (2009).
39 Oasis of the Deep: Cold Water Corals of Canada. http://www.science.gc.ca/default.asp?lang=En&n=EE39B64D-1 accessed on October 31, 2010.
40 Pierce et al. (2006).
41 Okey et al. (2010).
42 Lehman (2002) project warming of lake surfaces by 2100 leading to accelerated dissolved oxygen use, and consequent oxygen depletion, which can limit habitat for various species of fish (Mortsch et al. 2003), and have various other negative ecosystem consequences. The all-scenarios range for 2100 (2090s), using best estimates, is 2.3-4.5°C.
43 Lemmen et al. (2008); Soja et al.( 2007); Burns et al.( 2003); Parmesan & Yohe (2003); Walther et al. (2002).
44 Chmura et al. (2005).
45 Jones et al. (2009).
46 Based on multiple model runs and comparing temperature increases from the 20th century to 2080s, Scholze et al. (2006) estimate a one-in-three chance of losing 20% of boreal forest at a global temperature increase over pre-industrial levels of 3.5°C (see Table 2; note that we added 0.5°C to reflect temperature change in 20th century).
47 Tundra loss could also be significant, as the boreal moves north. A moderate projection for 2100 for the replacement of tundra areas by forest is about 10% (Sitch et al.,[ 2003]; see Figure 15.3). The year 2100 (2090s) corresponds to a best estimate of 4.2°C above pre-industrial levels in the A2 scenario (likely range 3.3-5.3°C).
48 Beaubien & Freeland (2000), as referenced in Sauchyn & Kulshreshtha (2008).
49 Current land-based protected areas and parks, in Canada and globally, are likely to see significant changes in their biodiversity (Hannah et al. [2002]). Loarie et al. (2009) used B1, A2, and A1B scenarios (2050–2100) to estimate relative speeds required to keep pace with climate change per global ecosystem, taking into account habitat fragmentation. Based on current protected areas, they used the indicator “time for current climate to cross a protected area” to rank ecosystem vulnerability. From least to most changed, the ranking for Canadian ecosystems is tundra (mean 74.6), temperate coniferous forests (12.7), temperate grasslands, savannas and shrubland (1.8), temperate broadleaf and mixed forest (1.7), boreal forests / taiga (1.1). Temperature position on Degrees of Change is the range of best estimates for 2050s (low end of range) and 2100 (2090s) (high end of range), using B1 as lower bound and A2 as higher bound of range. Earlier work (Scott and Suffling [2000]) suggests that 75-80% of Canadian National Parks will experience shifts in dominant vegetation for a doubling of CO2.
50 See, for example, Kurtz et al. (2008) and Flannigan et al. (2005).
51 Amiro et al. (2001) noted that area burned had shown an increasing trend over the 1980–1999 period relative to previous decades.
52 Based on analysis on western North America using the A2 SRES, Balshi et al. (2009) projected an increase in the average area burned per decade on the order of 350 –550% by the last decade of the 21st century.
53 Flannigan et al. (2005) projected ~ 74%–118% increase in area burned by the end of this century compared to a 1961–1990 baseline for a 3 × CO2 scenario for Canada (a high global emissions scenario). In Flannigan et al., forest area burned in the west ranges from 200–400% increase. Temperature position on Degrees of Change is the likely range for 2100 (2090s) using an A2 SRES scenario (high global emissions).
54 Williamson et al. (2009); Fleming et al. ( 2002).
55 We select these as examples among many. In its 2007 scientific assessment, the Intergovernmental Panel on Climate Change indicated “about 20 to 30% species at increasingly high risk of extinction” at global temperatures 2°C above pre-industrial levels and “major extinctions around the globe” at about 4°C of global warming (Parry et al.
[2007], page 67, Table TS.3). Three key factors contribute to extinction risk: (1) a small range size, (2) a small population size, and (3) dependence on habitat or other species that are themselves at risk from a range of factors (e.g., pollution, overuse, poaching, climate change) (Rabinowitz et al., [1986], as cited in National Academy of Sciences [2010]).
56 Moore & Huntington (2008); Johannessen & Macdonald (2008).
57 Moore & Huntington (2008).
58 Stirling & Parkinson (2006).
59 Regehr et al. (2007). On the degrees of change diagram, this impact is positioned toward the lower end of the global temperature range projected for 2100 (2090s) to account for existing evidence of the threat. Note also that figure TS.6 in IPCC (2007) AR4 Working Group II technical summary indicates “extinction risk for polar species” at 2.5 degrees above pre-industrial levels.
60 Jones & Henry (2003). According to Hudson & Henry (2009), warmer temperatures and longer growing seasons have already started to increase plant productivity in tundra communities of the high Arctic.
61 Jessen & Patton (2008).
62 Scott et al.( 2002); Suffling et al.( 2002).
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