Global climate change will affect the physical, biological, and biogeochemical
characteristics of the oceans and coasts, modifying their ecological structure,
their functions, and the goods and services they provide. Large-scale impacts
of global warming on the oceans will include:
- Increases in sea level and sea-surface temperature
- Decreases in sea-ice cover
- Changes in salinity, alkalinity, wave climate, and ocean circulation.
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:
- Increased levels of inundation and storm flooding
- Accelerated coastal erosion
- Seawater intrusion into fresh groundwater
- Encroachment of tidal waters into estuaries and river systems
- Elevated sea-surface and ground temperatures.
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:
- As a component of vulnerability assessment of natural systems
- With an emphasis on market-oriented or nonmarket-oriented approaches
- With a focus on costs for infrastructure and adaptation options.
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