Memorandum submitted by Professor Robert
Nicholls, Flood Hazard Research Centre, Middlesex University
CLIMATE CHANGE
AND COASTAL
ZONES
1. The importance of coastal zones
Low-lying coastal zones are sensitive to climate
change, most particular sea-level rise. This is important when
considering sustainable development as coastal zones are among
the world's most diverse and productive environments and they
also provide home to much of the world's population. In 1990,
1.2 billion people (or 23 per cent of the world's population)
lived within 100 km and 100 m of a coastline. These "coastal"
populations are growing rapidly due to migration to the coast
and urbanisation: large increases in coastal population are expected,
particularly in south, south-east and east Asia and around much
of Africa. Coastal areas are already threatened directly or indirectly
by a range of coastal hazards such as erosion, saline intrusion,
flooding/storms and tsunamis. Human activity is also producing
profound changes to the world's coastal zone such as reducing
freshwater inputs, modifying sediment budgets, armouring the coast
and direct and indirect ecosystem destruction. Therefore, climate
change and sea-level rise are an additional pressure on
coastal areas, which will interact adversely with many of these
other trends, and will potentially hinder the goal of sustainable
development.
2. Climate change in coastal areas
Global warming is expected to lead to an increase
in global mean sea-level rise due to thermal expansion of warming
surface waters and the melting of small land-based glaciers such
as those in the Alps. During the 21st Century, Greenland and Antarctica
are expected to make little net contribution to sea level. The
IPCC Third Assessment Report estimated that global-mean sea levels
had risen 10 to 20 cm during the 20th Century and will rise between
nine and 88 cm (the mid estimate is 48 cm) from 1990 to 2100[9].
Thus, there is likely to be a significant acceleration of global-mean
sea-level rise during the 21st Century. At the regional and local
scale, future changes in sea level are more uncertain due to regional
climate change effects on sea level and geological processes influencing
land uplift/subsidence. As an example, deltaic areas are always
prone to subsidence, so higher rates of sea-level rise might be
expected in these areas. This has important implications for the
densely-populated deltas of Asia.
Many other climate factors will change in coastal
areas such as rising seawater temperature. Of particular interest
are possible changes in the track, frequency and intensity of
storm events. For instance, it has been argued that in a warmer
world more intense hurricanes are possible than occur today. However,
the uncertainties remain too large to be confident of the direction
of change, if any, and this is an important area for future research.
3. The impacts of climate change and sea-level
rise
With global warming and sea-level rise, the
IPCC Third Assessment[10]
concluded that 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.
Without appropriate adaptation, these physical
changes will lead to socio-economic impacts on human populations
and their activities, such as increasing flood losses and destruction
of beachfront investments. Most assessments to date have only
considered the potential impacts of sea-level rise on today's
world. These studies all suggest that impact potential in many
developing countries is large and increasing rapidly. Other studies
point to a global tendency for shoreline retreat on sandy shorelines,
and the observed sea-level rise during the 20th Century may be
a causal factor, although is still widely debated.
Natural ecosystems such as saltmarshes, mangroves
and coral reefs are already widely degraded by human activities.
Given sea-level rise, saltmarshes and mangroves may be further
degraded or lost. Coral reefs appear more threatened by rising
sea temperature, which could cause death of the reef in tropical
areas where corals are near the upper limit of their thermal tolerance.
In the longer term, rising CO2 levels could cause chemical changes
which would reduce the capacity of the reef to build upwards with
sea-level rise. In all cases, this will reduce the range of services
(eg, storm protection, fisheries, etc) that these ecosystems provide
to coastal communities.
4. Examples: Flood and Wetland Impacts
The impacts of sea-level rise on the incidence
of coastal flooding and coastal wetlands (excluding coral reefs)
have been modelled on a regional and global basis,[11]
[12].
In 1990, it is estimated that 10 million people/year experienced
flooding due to storm surge globally—nearly all these people
live in the developing world. Under a scenario of a 40-cm rise
in global sea level, business-as-usual socio-economic changes,
and no specific adaptation for sea-level rise, this increases
to about 90 million people/year or more by the 2080s. Many of
these people will experience flooding every year, suggesting severe
impacts and possible displacement of these impacted populations.
These results show that a relatively small global rise in sea
level (about 40-cm) could have significant adverse impacts on
coastal populations, if there is no adaptive response.
By the 2080s, a 40-cm rise in global-mean sea
level could cause the loss of up to 22 per cent of the world's
coastal wetlands. Based on projecting existing trends, direct
and indirect destruction by humans could cause greater losses.
In this situation, sea-level rise would reinforce other adverse
trends of wetland loss. The largest losses due to sea-level rise
will be where the tidal range is lowest such as around the Mediterranean
and Baltic, the Atlantic coast of Central and North America and
most small islands, including the Caribbean.
5. Vulnerable Regions
All coastal areas are vulnerable to these changes
to varying degrees. However, the impacts are likely to be felt
disproportionately in certain areas reflecting both natural and
socio-economic factors that lead to higher vulnerability. In absolute
terms, the affected people identified in the flood analysis discussed
in 4) are found around Africa, and most particularly, South and
South-East Asia, with lesser impacts in East Asia. The vulnerability
of Africa reflects rapid population growth, combined with a limited
capacity to implement flood management due to economic constraints.
The vulnerability in Asia reflects significant population growth
within the numerous large deltas, where implementing flood management
is much more expensive than in most other coastal settings. The
vulnerability of small islands, particularly low-lying coral atolls
such as found in the Maldives has been recognised for some time.
The flood analysis suggests that the islands of the Caribbean,
the Indian Ocean and the Pacific Ocean may experience the largest
relative increase in flood risk. This vulnerability reflects the
concentration of population around the coast, even on the "high"
islands. While they have not been examined in detail, other impacts
such as degradation of coral reefs would seem to make these areas
especially vulnerable to climate change. Further, adaptation options
in many small islands are more limited than other coastal regions.
National studies also identify hotspots of vulnerability.
For instance, Guyana and Suriname have a high impact potential
and have similar problems to many of the Asian deltas. This contrasts
with a lower vulnerability in most of South America. There is
a need for a systematic identification of similar hotspots at
a detailed level around the world to focus more detailed work
on impacts and adaptation.
6. Responses
Responding to climate change and sea-level rise
requires identifying the most appropriate mixture of mitigation
and adaptation. Mitigation could greatly reduce the risks associated
with sea-level rise and climate change, particularly in the long-term.
However, some climate change appears inevitable, so we must also
be prepared to adapt to these impacts,[13]
[14].
Adaptation acts to reduce the impacts of sea-level rise and climate
change, as well as other changes (as well as exploiting benefits).
Given the large and growing concentration of people and activity
in the coastal zone, autonomous (ie, spontaneous individual
and market-driven) adaptation processes are unlikely to be sufficient
to respond to sea-level rise. Further, adaptation in the coastal
context is almost universally seen as a public responsibility.
Therefore, all levels of government have a key role in developing
and facilitating appropriate adaptation measures. There are three
generic planned adaptation options for sea-level rise and climate
change:
— (Planned) Retreat—all
natural system effects are allowed to occur and human impacts
are minimised by pulling back from the coast;
— Accommodation—all natural
system effects are allowed to occur and human impacts are minimised
by adjusting human use of the coastal zone;
— Protection—natural system
effects are controlled by soft or hard engineering, reducing human
impacts in the zone that would be impacted without protection.
However, adaptation needs to be seen as a process
rather than just these technical measures. A particular issue
of interest is resolving conflicts between sustaining the human
use and ecosystem functioning of the coastal zone under climate
change and sea-level rise. There is a need to start strategic
planning of appropriate responses now, particularly enhancing
the technical and institutional capacity of coastal management,
which is under-developed in much of the world, including the most
vulnerable regions identified here. Given the wide range of existing
coastal problems, such planning and capacity building could have
immediate benefits.
7. Conclusions
The main conclusions are as follows:
— Climate change in coastal areas will
lead to global-mean sea-level rise, rising seawater temperatures
and possible changes in the track, frequency and intensity of
storms, among other changes. This is an additional stress on coastal
zones, which could hinder the goal of sustainable development.
— Most impact assessments have focussed
on the impacts of sea-level rise and no other climate change.
They identify a high and increasing impact potential in many developing
countries.
— The most vulnerable regions appear
to be Africa and parts of Asia, reflecting high and growing exposure
and the low economic base to support adaptation. However, in relative
terms, small islands, including the Caribbean, appear most vulnerable,
and they have some of the most limited adaptation options.
— Coastal ecosystems are also threatened
by climate change, although this requires more quantification,
particularly for coral reefs.
— A more detailed global analysis of
the different types of vulnerability is essential to focus work
on impacts and adaptation.
— An appropriate mixture of mitigation
and adaptation would be the best response to climate change. There
are a range of effective adaptation options, although they need
to be considered within the broad process of coastal management.
Therefore, enhancing the capacity for coastal management is a
fundamental step in adaptation to climate change and sea-level
rise.
Based on this, DFID could help to promote sustainable
development of coastal areas by:
— Encouraging efforts to improve our
understanding of vulnerability;
— Promoting more evaluation of the
implications of climate change in coastal areas, particularly
in the vulnerable regions identified above;
— Enhancing coastal management capacity
so that it can deal with the full range of issues, including climate
change.
Professor Robert Nicholls, Professor in Coastal
Geomorphology and Management,
Flood Hazard Research Centre,
Middlesex University
January 2002
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12
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13
Parry, M, Arnell, N, Mcmichael, T, Nicholls, R, Martens, P, Kovats,
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