Feedbacks to the climate system will occur through changes in ocean mixing, deep water production, and coastal upwelling. Collectively, these changes will have profound impacts on the status, sustainability, productivity, and biodiversity of the coastal zone and marine ecosystems.
Scientists recently have recognized the persistence of multi-year climate-ocean regimes and shifts from one regime to another. Changes in recruitment patterns of fish populations and the spatial distribution of fish stocks have been linked to climate-ocean system variations such as the El Niño-Southern Oscillation (ENSO) and decadal-scale oscillations. Fluctuations in fish abundance increasingly are regarded as a biological response to medium-term climate-ocean variations, and not just as a result of overfishing and other anthropogenic factors. Of course, such factors can exacerbate natural fluctuations and damage fish stocks. Global warming will confound the impact of natural variation and fishing activity and make management more complex.
Growing recognition of the role of understanding the climate-ocean system in the management of fish stocks also is leading to new adaptive strategies that are based on the determination of stock resilience and acceptable removable percentages of fish. We need to know more about these interactions. Climate-ocean-related changes in the distribution of fish populations suggest that the sustainability of the fishing industries of many countries will depend on increasing flexibility in bilateral and multilateral fishing agreements, coupled with international stock assessments and management plans.
Marine mammals and seabirds are large consumers of fish and have been shown to be sensitive to inter-annual and longer term variability in oceanographic and atmospheric parameters. Several marine mammal and bird species, including polar bears and some seabirds, may be threatened by long-term climate change.
Marine aquaculture production has more than doubled since 1990 and is expected to continue its upward trend. However, aquaculture may be limited if key fish species used in feed production are negatively impacted by climate change. Increases in seawater temperature may directly impact aquaculture; such increases already have been associated with increases in diseases and algal blooms.
The adaptive capacities of marine and coastal ecosystems varies among species, sectors, and geographical regions. In the broader oceans, marine organisms will be relatively free to move to new geographical areas; organisms in enclosed seas and coastal zones are more constrained by the physical features of the shore, making natural adaptation more difficult.
Coastal zones are among the world's most diverse and productive environments. With global warming and sea-level rise, many coastal systems will experience:
Tropical and subtropical coastlines, particularly in areas that are already under stress from human activities, are highly susceptible to global warming impacts. Particularly at risk are the large delta regionsespecially in Asia, where vulnerability was recognized more than a decade ago and continues to increase. Mid-latitude temperate coasts often comprise coastal plains and barriers and soft sedimentary cliffs and bluffs that have been the subject of historical and model studies, virtually all of which confirm the high vulnerability of these coasts. High-latitude coastlines also are susceptible, although the impacts in these areas have been less studied. A combination of accelerated sea-level rise, increased melting of ground ice, decreased sea-ice cover, and associated more energetic wave conditions will have severe impacts on coastal landforms, settlements, and infrastructure.
Coastal areas also include complex ecosystems such as coral reefs, mangrove forests, and salt marshes. In such environments, the impact of accelerated sea-level rise will depend on vertical accretion rates and space for horizontal migration, which may be limited by the presence of infrastructure. Many mangrove forests are under stress from excessive exploitation, and salt marshes are under stress from reclamation. Many coral reefs already are degraded. In such situations, ecosystem resilience will be greatly reduced through human impacts as well as rising sea levels, increasing sea temperatures, and other climate-ocean-related changes, including prevailing wave activity and storm waves and surges.
Progress in evaluating the potential effects of climate change and sea-level rise on socioeconomic systems has not been as substantial as that relating to biogeophysical impacts. With reference to coastal zones, socioeconomic impacts have been considered in several ways, including:
Three coastal adaptation strategies have been identified previously: protect, accommodate, and retreat. In the past few years, structural shore-protection measures have been reevaluated, and there has been greater interest in managing coastal retreat. Enhancement of biophysical and socioeconomic resilience in coastal regions is increasingly regarded as a desirable adaptive strategy but appears not to be feasible in many of the world's coastal zones. Additional insights can be gained by understanding adaptation to natural variability.
Although some countries and coastal communities have the adaptive capacity to minimize the impacts of climate change, others have fewer options; the consequences may be severe for them. Geographic and economic variability leads to inequity in the vulnerability of coastal communities and potentially in intergenerational access to food, water, and other resources. Techniques for the integration of biophysical and socioeconomic impact assessment and adaptation are developing slowly, while human population growth in many coastal regions is increasing socioeconomic vulnerability and decreasing the resilience of coastal ecosystems.
Integrated assessment and management of open marine and coastal ecosystems and a better understanding of their interaction with human development will be important components of successful adaptation to climate change. Also important will be integration of traditional practices into assessments of vulnerability and adaptation.
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