Climate Change and the Arctic
The global climate is changing. The impacts of climate change are being observed earlier in the Arctic, and with more immediate and severe consequences, than in most of the rest of the world. The Arctic is warming at a rate almost twice the global average and reductions in Arctic sea-ice and permafrost and changes in weather are increasingly visible. Arctic marine mammals are uniquely adapted to life in the Arctic. Many rely on the seasonal presence of sea-ice, and all depend on the unique ecosystems and immense biological productivity of the region. Both of these factors are influenced by changing climatic conditions.
The Marine Mammal Commission seeks to increase scientific understanding of the impacts of environmental changes to marine mammals by working with and bringing together experts to discuss what the latest science shows. The Commission engages with other agencies on policy and management actions, such as assessing the conservation status of species through Endangered Species Act (ESA) listings (e.g., of polar bears, ice seals, and walruses) related to these changes. The Commission supports baseline research and environmental monitoring in U.S. waters and around the Arctic to document changes to marine ecosystems.
The effects of a warming atmosphere on physical, chemical, biological, and human components of Arctic ecosystems are myriad, far-reaching, and accelerating. The warming has caused a cascade of physical changes, from direct effects such as the melting of sea-ice and sea level rise, to secondary effects such as decreased albedo (surface reflectivity) and coastal erosion, to tertiary effects such as the accelerated warming of the ocean due to feedback loops between different climate factors.
In addition, the increase of carbon dioxide (CO2) in the atmosphere has led directly to an increased concentration of CO2 in the oceans, and its chemical derivatives have caused increased acidity (decreased pH) of the water— known as ocean acidification—and “wholesale shifts in seawater carbonate chemistry” (Doney et al. 2009). At each stage in the cascade of physical and chemical changes biotic components of ecosystems are affected.
For millennia, the Arctic marine environment was dominated by the polar ice cap and its dynamics (Laidre et al. 2008, Polyaka et al. 2010, Kovacs et al. 2011). In winter, virtually the entire Arctic Ocean and its marginal seas were (and still are) ice-covered, with the ice extending into the adjacent sub-Arctic seas. In summer, the seasonal ice largely disappeared from the sub-Arctic and pulled away from some Arctic coastlines, but even at the height of summer, remained in much of the Arctic Ocean. This perennial ice was complex, varying in thickness, age, and degree of consolidation. Beyond the pervasive influence of the ice, the Arctic is also shaped by the extreme seasonal variation in day length and cold temperatures. The lack of light and cold that persist for much of the year are associated with an unproductive environment, while the constant sunlight and warmer temperatures in summer stimulate a strong pulse of productivity, without which few, if any, marine mammals would have been able to evolve and thrive there. There is still a sharp contrast between winter and summer in the Arctic but it is becoming less pronounced as Arctic warming diminishes the seasonal extent of ice cover and extends the period of productivity.
Arctic Adaptations of Marine Mammals
Arctic marine mammals have adapted to the extreme and seasonally varying Arctic environment, becoming highly specialized at using different habitats for reproduction, foraging, molting, and migration in different seasons (Kovacs and Lydersen 2008, Gilg et al. 2012, Harington 2008). Several authors have classified Arctic marine mammals with respect to their degree of specialization. Laidre et al. (2008) considered species “that occur north of the Arctic Circle for most of the year and depend on the Arctic ecosystem for all aspects of life” the most highly Arctic-adapted—these include bowhead whales, belugas, narwhals, walruses, bearded seals, ringed seals, and polar bears. Moore and Huntington (2008) split these into “ice-obligate” species (polar bears, walruses, bearded, and ringed seals) and “ice-associated” species (bowhead whales, belugas, and narwhals). For the core Arctic species, the presence of sea-ice may be both a barrier to movement and a source of protection from predators (i.e., killer whales and polar bears), storms, and extreme cold. At least until recently, competitors and disease organisms from outside the Arctic were few and human threats (e.g., from commercial fishing, shipping, and oil and gas) were largely absent (Ragen et al. 2008, Gilg et al. 2012). Environmental changes are changing all of these elements, and in the process, making at least some Arctic marine mammals more vulnerable (Lefebvre et al,. 2016, Moore 2016).
Environmental Changes and Impacts
As warming in the Arctic has progressed, sea-ice has changed in both quantity (reduction in ice extent and volume) and quality (sea-ice fragmentation, deterioration, and altered seasonality) (Stroeve et al. 2008, Wang and Overland 2009), with profound consequences for sea-ice dependent species (Kovacs and Lydersen 2008, Laidre et al. 2015). Such consequences may be in the form of both reduced fitness of individual animals and altered population parameters (Laidre et al. 2015). It is not known to what extent ice-breeding Arctic seals have the ability to switch from using sea-ice to land as a haul-out substrate or to make other behavioral adaptations to changing conditions (Kovacs and Lydersen 2008). Many Arctic marine mammals will also be affected indirectly as the food webs on which they depend undergo changes. Restructured food webs, changes in prey populations and the arrival of new marine mammal species (including new predators), competitors, and pathogens from more temperate seas will challenge the Arctic species (Burek et al. 2008, Kovacs and Lydersen 2008, Reygondeau and Beaugrand 2011, Gilg et al. 2012, Moore and Gulland 2014, Moore 2016).
The effects of climate change are expected to vary regionally across the Arctic in the degree of sea-ice loss, the persistence of intact sea-ice, and how food webs are impacted (Moore and Huntington 2008). Sea-ice loss has already been much more extensive in the Pacific sector of the Arctic leading to concern that ice-obligate species there may decline in number and/or be forced to adapt as coastal habitats disappear. In other areas such as the Canadian Archipelago, perennial ice is expected to persist longer and populations there remain relatively unaffected at present (Moore and Huntington 2008).
Although many scientists have emphasized known and expected negative impacts on Arctic marine mammals (e.g., Burek et al. 2008, Kovacs and Lydersen 2008, Huntington 2009, Evans et al. 2010, Wassmann et al. 2010, Kovacs et al. 2011, Laidre et al. 2015), some species or populations are likely to experience little change or benefit from more favorable conditions. For example, the body condition of bowhead whales has improved as the open water season has lengthened in the Beaufort Sea (Moore 2016).
Declines in the amount and thickness age of sea ice are creating more opportunities for human activity in the Arctic, with resulting impacts on marine mammals. The earlier disappearance of sea ice from coastlines coupled with the ice’s retreat farther from shore during the summer and tendency to remain offshore longer in the fall means there is now a large, growing seasonal window of open water. This creates opportunities for oil and gas exploration and development, shipping, tourism, commercial fishing, and military operations. These activities expose Arctic marine mammals to a variety of threats, including ship strikes, pollution, entanglement in fishing nets or lines, and exposure to human-caused sound and other forms of disturbance that previously either had been absent or had been present only on a much smaller scale.
If the potentially catastrophic impact of climate change on some Arctic species is to be avoided, the source of the problem on a global scale will have to be addressed. Regardless of the degree to which society and governments are able to alter the course of global warming, our challenge in the short-term is to understand the effects of climate change on the Arctic, and anticipate the impact on Arctic species and human communities to the fullest extent possible.
For additional information on the Marine Mammal Commission’s efforts in the Arctic, see our 2012 annual report.
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