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Page 15
PART I
HAZARDS TO HUMAN HEALTH FROM THE OCEANS
Part I of this report identifies areas where coordinated efforts
between the oceanograpic and medical communities will be required
to address the risks to human health generated by the oceans and to
evaluate the potential consequences of climate change for public
health. There are three chapters included in Part I. Chapter 1:
''Climate and Weather, Coastal Hazards, and Public Health,"
describes how public health is affected by marine processes such as
ocean-dependent weather and climate effects, tropical storms, and
estuarine and coastal circulation. Chapter 2: "Infectious
Diseases," covers the various waterborne marine infectious diseases
including bacterial, viral, and protozoal agents of disease. This
chapter also examines the effects of weather and climate on
vector-borne diseases, such as the increased prevalence of malaria,
a disease carried by mosquitoes, following an El Niño event.
Finally, in chapter 3: "Harmful Algal Blooms," the various
syndromes resulting from exposure to algal toxins are identified
and discussed with reference to the ecology and distribution of the
specific algae associated with these illnesses.
There have been several recent programs that have highlighted
the value of an interdisciplinary approach to the issues described
in the following chapters. Brief descriptions of three programs
appear in boxes in the appropriate chapter: HEED, in chapter 1; the
ENSO Experiment, in Chapter 2; and ECOHAB, in Chapter 3.
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16
From Monsoons to Microbes: Understanding the Ocean 's Role in Human Health
The continued high productivity of ocean waters is dependent on the renewal of
its life-giving resources: oxygen, carbon, minerals, and nutrients. This renewal occurs
through the inflow of rivers and stirring of the ocean basins by great global currents that
circulate waters from the surface down to the depths of all the major oceans and back to
the surface again (Plate I). Without this 'overturning' circulation, the surface waters
would become depleted of nutrients and the deep waters would become depleted of
oxygen, a stagnation observed seasonally in some freshwater lakes and in isolated marine
basins and some estuaries.
At the grand scale of the world ocean, the ventilation of the deep water is
achieved by cycles of evaporation and precipitation, heat exchange, winds, runoff of
fresh water from land, and freezing and thawing of ice. As surface waters are cooled,
they become more dense and sink, bringing oxygen-rich water to the deep. This causes
stratification, where dense (cold or more saline) waters slip beneath buoyant (warm or
less saline) waters. However, this atmospheric-driven sinking occurs only in very
narrow, concentrated currents, whereas water rises toward the surface much more
broadly. This results in the asymmetric creation of stable, stratified water masses.
Stratification is perhaps the most important physical property of the ocean for life
on earth because it determines the distribution of nutrients and oxygen. Even though the
deep waters are only about 0.3% denser than surface waters, this difference is sufficient
to segregate water masses and hence the sources and sinks of biological activity.
Biological production depends on the input of nutrients into surface waters where there is
sufficient sunlight for photosynthesis. Zones of high productivity occur where the
nutrients and oxygen enriched deep waters are brought to the surface by physical forces,
such as wind-driven upwelling or tides. In some areas, upwelling is driven by the force
of the wind on the sea surface, pulling water up from depths of 100 m (328 feet) or more.
In coastal waters and estuaries, nutrient input from rivers may be dominant. The lower
density of freshwater keeps these nutrients stratified at the surface creating zones of high
biological productivity.
Stratification of water masses with different temperatures and salinities also
influences climate and local weather systems that in turn affect human health, both
through severe storms and through changes in climate that alter the range of agents of
infectious disease. This chapter will discuss why physical ocean properties have
important implications for public health.
Public Health Problems Caused by Tropical Storms
and Other Marine Natural Disasters
Natural disasters involving ocean processes include phenomena such as rain,
tropical storms, tsunamis, storm surges, blooms of toxic algae, pathogen contamination
of coastal waters, and recurring as well as long term climate variability. The types of
problems faced by the public health system are determined both by geography and the
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1
Climate and Weather, Coastal Hazards, and Public Health
The Physical Ocean Environment:
Circulation and Stratification
Public health policymakers rely on the ocean sciences to help
them develop more effective responses to marine hazardous phenomena
including tropical cyclones and hurricanes, tsunamis (or long
oceanic waves), toxins and pathogens in nearshore and estuarine
waters, and ocean-driven weather and climate patterns. These events
may either directly cause injury and death or indirectly cause the
spread of various types of illness, including waterborne and
vector-borne diseases, as well as illnesses associated with toxic
algal blooms. The protection of public health requires a thorough
understanding of the physical ocean environment for better
forecasting and handling of marine disasters. This chapter will
describe the major threats to public health and the ocean processes
that contribute to them.
Frequently, the ability to anticipate and respond promptly to
natural disasters rests on an understanding of weather systems that
depend on a complex coupling of the atmosphere, land, and the
ocean. The ocean absorbs immense quantities of heat, fresh water,
and carbon, and hence act as the "memory" of the atmosphere and
land. Although climate is seen more readily by observing the
atmosphere, it is the coupled system of the ocean, the atmosphere,
and the land masses that determines the evolution of climate over
long periods of time. Beyond its role as a reservoir for water,
heat, and carbon, the world ocean actively influences the
atmosphere, as demonstrated by the El Niño phenomenon. In an
El Niño, the normal upwelling of cold water along the
Equator fails, and a lens of warm tropical surface water spreads
across the eastern Pacific. These warm ocean waters
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contribute moisture and energy (in the form of heat) to the
atmosphere and bring unusually warm, wet weather to the west coasts
of North and South America, and droughts to Australia and southeast
Asia.
The ocean also serves as the medium for the culture of
phytoplankton, microalgae that produce oxygen as a by-product of
photosynthesis and account for about 50% of the earth's primary
productivity. Through the consumption of seafood, many human
populations depend on this resource. In general, the productivity
of the world's oceans, which includes fisheries, is a reflection of
the primary productivity of the phytoplankton. However, these
phytoplankton also pose public health problems because some species
produce toxins that cause various illnesses when they are consumed
in seafood, as described in more detail in chapter 3. Hence, it is
important to know what properties of the marine environment
influence the productivity of phytoplankton.
The continued high productivity of ocean waters is dependent on
the renewal of its life-giving resources: oxygen, carbon, minerals,
and nutrients. This renewal occurs through the inflow of rivers and
stirring of the ocean basins by great global currents that
circulate waters from the surface down to the depths of all the
major oceans and back to the surface again (Plate I). Without this
"overturning" circulation, the surface waters would become depleted
of nutrients and the deep waters would become depleted of oxygen, a
stagnation observed seasonally in some freshwater lakes and in
isolated marine basins and some estuaries.
At the grand scale of the world ocean, the ventilation of the
deep water is achieved by cycles of evaporation and precipitation,
heat exchange, winds, runoff of fresh water from land, and freezing
and thawing of ice. As surface waters are cooled, they become more
dense and sink, bringing oxygen-rich water to the deep. This causes
stratification, where dense (cold or more saline) waters slip
beneath buoyant (warm or less saline) waters. However, this
atmospheric-driven sinking occurs only in very narrow, concentrated
currents, whereas water rises toward the surface much more broadly.
This results in the asymmetric creation of stable, stratified water
masses.
Stratification is perhaps the most important physical property
of the ocean for life on Earth because it determines the
distribution of nutrients and oxygen. Even though the deep waters
are only about 0.3% denser than surface waters, this difference is
sufficient to segregate water masses and hence the sources and
sinks of biological activity. Biological production depends on the
input of nutrients into surface waters where there is sufficient
sunlight for photosynthesis. Zones of high productivity occur where
the nutrients and oxygen enriched deep waters are brought to the
surface by physical forces, such as wind-driven upwelling or tides.
In some areas, upwelling is driven by the force of the wind on the
sea surface, pulling water up from depths of 100 m (328 feet) or
more. In coastal waters and estuaries, nutrient input from rivers
may be dominant. The lower density of freshwater keeps these
nutrients stratified at the surface creating zones of high
biological productivity.
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Stratification of water masses with different temperatures and
salinities also influences climate and local weather systems that
in turn affect human health, both through severe storms and through
changes in climate that alter the range of agents of infectious
disease. This chapter will discuss why physical ocean properties
have important implications for public health.
Public Health Problems Caused by
Tropical Storms and Other Marine Natural Disasters
Natural disasters involving ocean processes include phenomena
such as rain, tropical storms, tsunamis, storm surges, blooms of
toxic algae, pathogen contamination of coastal waters, and
recurring as well as long-term climate variability. The types of
problems faced by the public health system are determined both by
geography and the socioeconomic status of the affected country.
While the wealthier industrialized nations suffer more economic
loss, poorer developing countries often face far greater loss of
life, continuing incidence of disease, and longer lasting damage to
social and physical structures. The potential for immediate
casualties and communicable disease outbreaks often overshadows the
more severe and durable long-term impacts on public health, even in
developing nations. Both the direct and indirect impacts of marine
natural disasters are assessed here with primary consideration
given to the impacts of tropical storms, tsunamis, and storm
surges. The public health issues arising from the spread of
pathogens and harmful algal blooms will be discussed in Chapters 2
and 3, respectively.
Risk is a measurement of the degree of loss (human life,
injuries, economic losses, etc.) expected by the occurrence of a
disaster. Short- and long-term health consequences are a result of
the contributions of many factors, such as:
•
The type of disaster: tropical storms, storm surges, tsunamis,
and gradual climate changes (from floods to drought). Loss of human
lives is particularly severe following storm surges.
•
The type of housing and other construction in the affected
community: tropical storms will have different immediate health
consequences in a poor island with highly vulnerable wooden housing
than in a metropolitan area such as Miami.
•
The level of economic development: although closely associated
with the housing type, the economic level will determine the
capacity of the community to respond and recover from the impact,
therefore natural disasters affect the poor disproportionately.
•
The level of preparedness of the community and health services.
A well-educated population and an effective warning system will
save many lives.
•
The level of vulnerability as determined by local landuse
practices, e.g., deforestation is believed to have contributed to
the mudslides in Honduras and Nicaragua following Hurricane Mitch
in 1998.
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•
Most critically, the vulnerability of the community as
determined by the overall health and incidence of communicable
diseases prior to the impact.
These factors explain why mortality and morbidity caused by the
same weather event may vary widely from one country to another.
Direct Impacts on Health
Mortality, the number of deaths caused by natural disasters, is
the most common indicator used by the international community to
assess the severity of the health impact of a disaster. The number
of lives lost provides important statistical data but can be highly
misleading in determining the impact on survivors.
High mortality resulting from marine disasters is associated
with tsunamis, storm surges, and flash floods resulting from
tropical storms with heavy precipitation. For example, a cyclone in
the Bay of Bengal in 1970 induced a storm surge causing between
250,000 and 500,000 deaths (Murty et al., 1986; Sommer and Mosley,
1973). The broad range in estimating mortality following the
Bangladesh cyclone reflects the lack of reliable data on the
consequences of natural disasters in most developing countries.
Also, this dramatic loss of life illustrates the high-risk to the
population in Bangladesh—a combination of the frequent
occurrence of cyclones and storm surges with an extremely
vulnerable and unprepared population. At the other end of the
spectrum, accurate forecasting of tropical storms in the Caribbean
region and effective evacuation policy and procedure have greatly
reduced the loss of lives from recent hurricanes in the United
States, although there is still potential for significant loss of
life due to tropical storms (Pielke and Pielke, 1997).
The devastating 1998 tropical storm season in the Caribbean
illustrates the disproportionate effects of hurricanes on
developing and industrialized nations. Hurricane Georges, which
struck the Caribbean and U.S. Gulf Coast in September of 1998, was
responsible for an estimated 210 deaths in the Dominican Republic
while causing fewer than 10 fatalities in the U.S. and Cuba (AP,
1998a).
At the end of October 1998, Hurricane Mitch brought tragedy to
Central America when the storm stalled over the coast of Honduras
and dropped torrential rains in the highland and coastal regions
for several days. The rains caused catastrophic floods and
landslides throughout the region, with Honduras suffering the
heaviest losses. In Honduras, Nicaragua, Guatemala, and El Salvador
there were an estimated 9000 deaths with another 9200 people
reported missing. More than half of the casualties occurred in
Honduras, where approximately 12,000 people were injured and 1.5
million were affected by the storm and its aftermath (USAID, 1998;
UN, 1998). The devastation brought by Hurricane Mitch was not a
result of poor prediction, but instead illustrates how natural
disasters can result when poverty drives the development and
deforestation of vulnerable areas (Copley, 1998; LaFranchi,
1998).
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Tsunamis are long oceanic waves caused by earthquakes that
displace the seabed. Although tsunamis occur less frequently than
tropical storms, some predictions allow vulnerable communities to
be warned in advance. As with a storm surge, mortality is high in
low-lying coastal areas. On July 17, 1998, a shallow earthquake
near the coast of Papua, New Guinea drove a wave onshore,
inundating a strip of heavily populated shoreline. The first wave
approached 30 feet in height and arrived 9 minutes after the
earthquake (Plate II). The sudden influx of water resulted in more
than 2000 deaths. Because the earthquake was so close to shore, no
form of prediction and warning system could have prevented this
loss of life. In many other cases, earthquake epicenters are far
from vulnerable shores and warnings are effective. Elaborate
warning networks are in place on many Pacific islands and around
the Pacific rim.
The human health risks from the Papua, New Guinea tsunami
situation were so great that officials declared a state of
emergency on the Sissano coast and sealed off an area of about 120
square kilometers (45 square miles) around the lagoon. The
devastation of this area forced crowding of displaced residents
onto higher land. Such crowding in a wet environment, along with
disruptions in the supply of potable water, favors the spread of
infectious diseases such as pneumonia, cholera, and malaria. In
addition, most of the injuries suffered by survivors were open
wounds as a result of the physical force of the tsunami. The
greatest danger to the injured therefore was infection because of
limited medical care in the immediate aftermath of the
disaster.
Although epidemics of waterborne (diarrheal diseases including
cholera and typhoid fever) or vector-borne diseases (such as dengue
fever and malaria) are a major concern, remarkably few major
outbreaks have been scientifically documented in the literature
following such natural disasters. Typically, in the Bay of Bengal,
storms surges may cause greater problems from the salination of
wells and agricultural lands than the contamination of water with
pathogens. The absence of anticipated disease outbreaks may reflect
several factors. First, water-borne diseases are highly preventable
through public and individual environmental health measures. The
very fear of devastating outbreaks is an effective incentive to
improve otherwise neglected basic sanitation and water control in
many countries. Second, dilution of fecal contamination by tropical
storm surges in overcrowded and heavily contaminated environments
may reduce outbreaks. Finally, the health indicators of the
surviving population, in some instances, appears to improve in the
case of a disaster such as a storm surge because the death toll is
highest among the elderly, children, and the sick—groups with
the greatest health problems (Chen, 1973; Sommer and Mosley,
1972).
In the case of vector-borne diseases, tropical storms, floods,
and storm surges may either suppress or promote the breeding of the
vector and its pathogen. Initially, the influx of water may disrupt
insect vector breeding sites and decrease the rodent vector
population. Later, however, breeding sites for mosquitoes (the
vector for malaria, dengue, and yellow fever), while initially
washed away by the
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floods or storm surge, increase with the use of residential
water pools that build the potential for increased transmission.
For example in 1963, Hurricane Flora struck Haiti shortly after the
completion of insecticide spraying of the dwellings by the malaria
eradication program. The proliferation of breeding sites combined
with a disruption of routine control measures resulted in one of
the best-documented hurricane-caused outbreaks of malaria, (Mason
and Cavalie, 1965).
Indirect Impacts on Public Health
The pursuit of public health encompasses much more than the
provision of medical care or the control of communicable diseases.
In the constitution establishing the World Health Organization
(WHO), health is defined as "a state of physical, mental, and
social well-being and not only the absence of disease or infirmity"
(WHO, 1946).
The delayed or indirect health impact of marine natural
disasters is generally underestimated and under-reported. The long
term cost to public health results from the interruption of health
services, the permanent damage to infrastructure, the setback in
development, and the loss of individual income. In the developing
countries, electrical power and potable water shortages or
rationing are daily occurrences. Following an ocean-borne disaster,
the lack of electrical power (and transportation) has profound and
far reaching public health consequences, affecting the operations
of hospitals, water plants, and health facilities, as well as
degrading the quality of the local environment. As summarized
below, loss of these capabilities has the potential to affect
public health more profoundly than the immediate impact of an event
such as a storm surge.
Disruption of health services: Following a disaster in
developing nations, health services experience a decreased ability
to respond to normal demands for medical care. Hurricane Gilbert in
Jamaica (1988) left a modest toll of 45 people dead, but twenty-two
hospitals or health centers were out of service for an extended
period of time and 90% of the hospital bed capacity was unavailable
for several days to several weeks (Table 1-1; PAHO, 1988; Zeballos,
1993).
Setback in development: The economic impact of natural
disasters at a national level is amplified in the health sector for
several reasons. Existing resources (medicines and disposable
equipment, budget, personnel) are diverted from routine medical
care and disease control programs for immediate response to the
perceived threats to public health. International assistance,
however generous, rarely represents a significant proportion of the
material emergency contribution and does not subsidize the future
provision of routine care and disease control.
Loss of individual income: Even if the economy of the
developing country is not significantly affected by the disaster,
the most economically vulnerable population
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Representative terms from entire chapter:
natural disasters
Page 23
TABLE 1-1 Loss of Hospital Bed Capacity
Type of Disaster
Number of Health Facilities Affected
Number and Percent (%) of Beds Lost
Hurricane Gilbert, Jamaica (1988)
22
5,065 (90%)a
Hurricane Hugo, Montserrat (1989)
1
67 (100%)
Tropical Storm Debbie, St. Lucia (1994)
1
25 (13%)
Hurricane Luis, Antigua (1995)
1
24 (16%)
Hurricane Luis and Marilyn, St. Kitts (1995)
1
102 (68%)
Hurricane Georges, St. Kitts (1998)
1b
170 (100%)
a Includes
beds briefly unavailable in the immediate aftermath, in over 500
affected health care centers.
b Same
hospital as in 1995.
SOURCE: Pan American Health Organization (PAHO),
Regional Office of the World Health Organization (WHO), 1998.
is likely to suffer—poverty is the major global cause of
illness and poor health (Hahn, 1996; McIntyre, 1997; PAHO, 1998a).
When a family's income is reduced, there is decreased access to
food, medical care, clean water, and other critical services.
Therefore, the mortality and morbidity arising from the
immediate impact of marine natural disasters does not necessarily
predict the long-term effects on public health. The loss of
community services and secondary effects on the economy may have
more serious impacts. The challenge to the international community
is to help communities establish the infrastructure necessary to
improve warning systems and to implement protective and preventive
measures.
Forecasting Tropical Storms
Vulnerability
The vulnerability of the United States to damages from tropical
storms1 is higher now than in the
past because of the growth and increased wealth of the coastal
population; the population has been increasing at a rate of
4–5% per year (Sheets, 1990). Millions of people live and
vacation along the coastline and are exposed to the threat of
tropical storm winds, rain, storm surge, and severe
1Tropical
storms is used as a general term to describe tropical storms and
hurricanes, and cyclones.
Page 24
weather. During this century, improved forecasts and warnings,
better communications, and increased public awareness have reduced
the loss of life associated with tropical storms in the United
States. However, tropical storm-related damage has increased
dramatically. Hurricane Andrew, in 1992, was the most costly
natural disaster in U.S. history in terms of physical damage,
although the loss of life was relatively low. The higher level of
damages in the past decade is not from an increase in hurricane
frequency, but reflects inflation, expansion of the coastal
population, and the increased wealth of coastal communities (Pielke
and Landsea, 1998).
The public's vulnerability is a function of the skill in
forecasting the intensity of wind, rain, storm surge, and severe
weather near landfall. While specific track prediction models have
shown up to a 15% improvement, there has been little improvement in
the prediction of intensity change (Elsberry et al., 1992). For
this reason, the average length of coastline warned per storm,
about 354 miles, has not changed much over the past decade.
However, the average preparation costs increased six-fold in the
past seven years, from $50M per storm in 1989 to an estimated $300M
per storm in 1996 (OFCM, 1997). Unless the rate of forecast
improvements can be accelerated, the downward trend of tropical
storm casualties is not likely to continue, and the damage will
continue to escalate. Track prediction is made more difficult by
decadal climate variability, which leads to long-term variation in
the frequency, intensity, origins, and paths of hurricanes.
Each improvement in tropical storm forecasting has been achieved
by taking advantage of better observations. New strides in our
abilities have always paralleled by development of new research
tools; from instrumented aircraft, to radar and satellites. Because
storms originate in the tropical ocean where few data are
available, the scientific community has pioneered mobile observing
strategies in order to provide critical observations of the storm's
location and strength. One example is the production of high
quality images of tropical storms produced by the SeaWiFS satellite
(Plate III). These techniques have evolved to include measurements
of the upper ocean and atmosphere in the vicinity of the storm.
High-quality, high-resolution observations provide essential data
used in determining parameters for models of atmospheric, oceanic,
or coupled processes. A synergism between observations and models
is required to isolate the important physical processes that will
allow more accurate forecasts.
The Federal Emergency Management Agency (FEMA) requires coastal
communities with limited escape routes to have completed
preparation and evacuation before the arrival of gale force winds,
typically 24 h to 48 h before landfall. However, an inadequate
understanding of the fundamental mechanisms that inflict damage
impairs our ability to provide timely warnings. Errors in wind,
storm surge, and rainfall forecasts have prevented officials from
accurately defining the most vulnerable regions in order to
expedite required preparations well in advance of the projected
landfall. Hurricane Opal provides an example of this as described
below.
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Hurricane Opal
During the evening of October 3, 1995, Hurricane Opal was
located in the southern Gulf of Mexico [for a summary of Hurricane
Opal and its impacts see the National Oceanic and Atmospheric
Administration (NOAA) Service Assessment Team Report (NOAA, 1996)].
The storm had been slowly intensifying over the previous three days
while drifting slowly over the Gulf of Campeche. Given the small
basin size of the Gulf of Mexico, Opal could strike anywhere along
the U.S. Gulf Coast within 24 h.
In the middle of the night on October 3, the storm started one
of the most rapid deepening and intensification cycles that has
ever been observed as it moved at 19 miles per hour (MPH) toward
the U.S. Gulf Coast. Within a 5 h period, U.S. Air Force Reserve
(AFRES) reconnaissance aircraft measured a steep central pressure
drop (939 hPa2 to 916 hPa),
estimated surface winds increased to nearly 157 MPH, and the radius
of the eye of the storm contracted from 19 to less than 10 miles.
This rapid deepening presented the hurricane specialists with a
major problem when the storm approached category 5 status within 12
hours of landfall without any means of alerting the public.
Fortunately, over the subsequent 6 hours, the storm strength
dissipated before reaching landfall later in the afternoon (Plate
IV). Despite this weakening, the storm surge and wave activity were
greater than anticipated and caused extensive damage along the
coast, while wind damage and rainfall were less than forecast for a
storm of that strength (NOAA, 1996). In forecasting this storm, why
was the surge and the extent of the severe weather greater than
predicted, while the wind damage and rainfall were less than
predicted?
Crucial unanswered questions concerning the change in tropical
storm intensity lie in three major components: (1) upper ocean heat
content and the subsurface ocean structures that affect it
(Elsberry et al., 1976; Black, 1983; Shay et al., 1992); (2) the
inner core dynamics of storms; and (3) the winds at the jet-stream
level, which are influential in steering cyclones. Important
programs addressing these issues include the Tropical Cyclone
initiatives of the Office of Naval Research (Elsberry, 1995) and
observations and modeling by NOAA's Hurricane Research Division.
These studies have demonstrated that accurate profiles of
atmospheric variables obtained from aircraft deployed
dropwindsondes are important for track prediction.
Ocean's Role in Modulating
Intensity
The ocean's influence on tropical storm pressure and wind
variations is dependent on the transfer of heat from the surface
waters to the atmosphere. The recent case of Hurricane Opal
demonstrated that sudden unexpected intensification
2hPa =
hectoPascals.
Page 32
stratification, tidal currents, and topographic features that
create complex circulation patterns not detected by broadly-spaced
current meter arrays. Hence predicting particle transport at any
particular time or location will require detailed models and/or
extensive real-time monitoring systems.
Estuaries also form the conduit for the transport of high
concentrations of land-derived nutrients and pollutants into
coastal waters. Despite recent reductions in the input of toxic
materials to U.S. waterways, concerns about coastal pollution
remain regarding bioaccumulation, ecological and human health
effects (NRC, 1994b). Nutrients are essential for the support of
fisheries in coastal waters. As mentioned earlier, sometimes these
nutrients stimulate large blooms of plankton that can result in
oxygen-depleted areas, that are either hypoxic (low oxygen) or
anoxic (no oxygen). This problem is particularly severe in the Gulf
of Mexico, adjacent to the outflow of the Mississippi and
Atchafalaya Rivers, where a low oxygen ''dead zone" forms during
the summer months that covers roughly 7000 square miles.
Several mechanisms have been proposed whereby nutrient-laden
waters from estuaries mix across coastal waters and the continental
shelf: (1) upwelling-favorable winds displace the low-salinity
waters offshore, (2) winds from storms yield vertical mixing that
homogenizes the water column, and (3) instabilities in flow allow
the coastal current to shed eddies into the central shelf
region.
In addition to transporting nutrients offshore, these processes
also transport minute marine organisms such as dinoflagellates. In
the Gulf of Maine, plumes of lower salinity estuarine water have
been found to harbor the toxic dinoflagellate Alexandrium
tamarense in high concentrations. Upwelling pushes the algae
offshore and disperses the bloom while downwelling, when the winds
reverse, causes the algae to accumulate at high concentrations
along the coast where shellfish beds are more likely to become
contaminated (Franks and Anderson, 1992a,b).
Similarly, coastal currents provide a potential route for the
transport of toxic dinoflagellates from one region to another. The
three mixing processes described above may move phytoplankton from
a contaminated coast to offshore waters where currents may carry
them to new downstream locations. In this new area, a relaxation of
upwelling, associated with a shift in wind direction, will
transport the dinoflagellates to coastal waters, hence creating
conditions for a toxic bloom in a place where the phytoplankton had
never been seen before. This scenario has been used to explain
outbreaks of paralytic shellfish poisonings caused by a toxic
dinoflagellate in the oceanic bays along the northwest coast of
Spain (Fraga et al., 1988). An "upwelling index" (Bakun, 1973),
based on meteorological pressure fields, has been used to
investigate whether this physical feature can be used to predict
blooms of toxic algae in this area. In this way, the use of
hydrographic data obtained by studying physical processes may
someday allow health officials to anticipate outbreaks of harmful
algal blooms before the public is exposed to contaminated
seafood.
Page 33
Climate Variability and Global Climate
Change
When climate change persists over long time-scales (greater than
one year), the consequences for human health tend to be more
serious. Regional drought, for example, can be withstood for a
limited time (more so in industrialized countries) but after a
prolonged period leads to famine and displacement of populations.
In drought-stricken areas, higher temperatures change regional rain
patterns and affect agricultural productivity, thus disrupting
local food supplies. In other areas, climate variability may bring
increased rainfall. Dependent on the region, these changes may
alternatively increase or decrease agricultural productivity and
the potential for outbreaks of waterborne diseases. Also, higher
temperatures could increase or decrease the range and abundance of
insect and rodent vectors of disease, possibly spreading diseases
such as rift valley fever and malaria to new areas. Finally,
climate change could lead to an increase in heat-related deaths,
including deaths from respiratory diseases caused by air pollution
which is expected to be more severe with longer, warmer summers.
Although death rates increase at both temperature extremes (heat
waves and extreme cold), heat-related deaths are predicted to more
than offset a reduction in winter mortality (Pearce et al.,
1995).
Temperature and rainfall patterns, while most often thought of
as atmospheric phenomena, actually involve the interaction of the
atmosphere with the ocean and the land, particularly for long-term
climatic changes. In this coupled system, the ocean serves as the
major reserve of heat and moisture. Attention has centered on
sea-surface temperature, however, it is actually the available heat
content of the upper-ocean that counts. The size of this reservoir
is in part determined by salinity stratification and ice cover as
well as by temperature fields. These variables, which affect the
capacity of the ocean to absorb and transmit changes in atmospheric
conditions, are key factors in assessing the risks posed by climate
change and variability.
El Niño/Southern Oscillation
(ENSO) and the North Atlantic Oscillation
(NAO)
The El Niño/Southern Oscillation (ENSO) and the North
Atlantic Oscillation (NAO) serve as examples of recurring weather
patterns that take place on time scales longer than one year. El
Niño recurs every 3–7 years, when the prevailing
easterly (westward) winds of the tropical Pacific fail. This
suppresses the upwelling of cold, nutrient-rich water along the
central and eastern equatorial Pacific and releases a pool of warm
water from the western end of the Equator. This pool of warm water
propagates eastward across the equatorial Pacific towards the
western hemisphere.
Sometimes the human health consequences of ENSO weather are
severe. The immediate results of a warmer sea surface are increased
rainfall in the eastern
Page 34
Pacific and decreased rainfall in the Asian sector. Australia
typically experiences severe drought. The yearly migration of the
Asian monsoons also correlates with ENSO, bringing drought to some
parts of Africa and India. The sea surface temperature (SST)
anomalies in the central equatorial Pacific correspond to an
atmospheric response that propagates along a great-circle path over
North America yielding increased rain and storminess in the
southwestern and southeastern U.S. Changes in temperature and
rainfall due to ENSO have been postulated to lead to outbreaks of
malaria and cholera, however, this proposed link is controversial.
This issue is covered in greater detail in the following chapter on
infectious diseases.
NAO is a mode of variability in the atmosphere over the North
Atlantic. It has a very broad spectrum of time-scales, from days to
centuries. It was discovered in atmospheric pressure records by
18th century missionaries in Greenland who observed that cold
winters there often occurred when Scandinavian winters were mild,
and vice versa. The NAO is in part a strengthening or weakening of
the Icelandic low-pressure center that dominates North Atlantic
weather, a statistical result of changes in the path and intensity
of wintertime storms that grow over the northern Atlantic Ocean.
The NAO also correlates with a large stratospheric vortex that is
centered over the North Pole (Perlwitz and Graf, 1995; Thompson and
Wallace, 1998).
The NAO index, which describes the waxing and waning of this
phenomenon, correlates strongly with many weather variables
relating to human health. Temperatures and precipitation in
northern Europe, northwest Africa, and the Middle East are
particularly affected. The precipitation and river-flow rate in the
Tigris-Euphrates is correlated with the NAO (which corresponds to
about 70% of the observed variability). Regions like this, with
limited fresh-water supply, are sensitive to this degree of change.
Since the 1960s the positive NAO phase has corresponded to droughts
in southern Europe and the Mediterranean (Hurrell, 1995) and
decreased rainfall in Morocco (Lamb and Peppler, 1987).
Global Warming, Global Change: Gradual
and Abrupt Climate Change
Recent weather records reveal that over the past century the
climate we have experienced is at least as warm as any century
since 1400 AD, possibly due to increases in greenhouse gases. A
trend towards a warmer world is emerging from the complex spectrum
of natural variability (Nicholls et al., 1995). The global-average
surface temperature in 1997 was the warmest of the century (Figure
1-3) and probably the warmest of the past 1000 years, while the
past 8 years have included the 3 warmest years since at least AD
1400 (Mann et al., 1998). In 1998, each month set a new record for
globally averaged surface temperature.
However, this change is far from uniform. A pattern of response
"modes" appears to be involved, in which warming is concentrated in
northern Asia (which has seen up to a 3.5 ¹C warming in
average wintertime surface air temperatures
Page 35
FIGURE 1-3
Global surface air mean temperatures show a warming trend during
the 20th century.
Since 1980 this warming has accelerated, with 1997 being the
warmest year this century.
Temperature changes in a complex pattern, with the oceans showing
moderate increases compared
with the strong warming over land, particularly at high latitudes
in northern Asia and northern North America.
These patterns suggest an important role for atmosphere/ocean
dynamics in global warming (NOAA, 1998b).
between 1980 and 1997) with lesser warming in western North
America, while large regions of the North Pacific and North
Atlantic Oceans and their neighboring shores have actually cooled
since the 1960s. Many climate variables are affected. Water
transported in streams and rivers in North America has increased
significantly, along with precipitation (Nicholls et al.,
1995).
Warming of the lower atmosphere is particularly rapid over far
northern land masses such as central Asia and western Canada. In
Alaska, the front of the Columbia glacier has retreated 8 miles
inland over the past 16 years, and no longer reaches Glacier Bay.
As global surface temperatures have increased by 0.3–0.6
¹C during the last century, the maximum recent warming has
occurred in winter over the high mid-latitudes of the Northern
Hemisphere (Nicholls et al., 1995). This warming has been
especially marked for the period from 1975–1994,
Page 36
which correlates with unusual ENSO activity (Nicholls et al.,
1995) and analysis of paleoclimate indicators suggest that 1990,
1995 and 1997 were warmer than any of the last 500 years (Mann et
al., 1998). The warming trend is expected to continue, with brief
warming and cooling events expected as part of the natural
variability. Although there is variability in outcomes from
computer models of the coupled atmosphere/ocean/land system, some
predict that in a world with twice the current atmospheric CO2 levels there will be a nearly 50%
increase in high northern latitude precipitation (minus
evaporation) combined with significant warming (Manabe and
Stouffer, 1994). The predicted global-average warming over the next
50 years (to the year 2050) ranges from 0.7 to 2 ¹C, with
values much greater than this over land and at high latitudes.
Although such change is still very speculative, it is the common
outcome of these models.
In this century, the occurrence of the two strongest El
Niño events (1982/3 and 1997/8), and the occurrence of the
strongest positive phase of the NAO (1972–1995) have led to
speculation that global warming influences these events. This
recent NAO has yielded the strongest Icelandic low observed in the
past 120 years, with a northward displacement and intensification
of storms and strengthened deep convection in the ocean (Dickson et
al., 1996). Both ENSO and NAO affect analysis of global warming
through their direct impact on surface temperatures. Hence there is
an interconnection between global warming, ENSO, and NAO which
complicates the prediction of future events.
Effects of global warming on other weather patterns such as
tropical storms are difficult to predict. Nevertheless, recent
analyses suggest that there are no global historical trends in
tropical storm number, intensity or location and current
thermodynamic models predict a modest (10–20%) increase in
maximal potential storm intensity for a doubled CO2 climate that is small compared with
natural variations (Henderson-Sellers et al., 1998). However, the
continuing rise in sea level, described below, will contribute to
the impact of tropical storms through the elevation of the base for
storm surges (NRC, 1998a). Potential effects of global warming on
major weather events like ENSO may also influence tropical storms.
ENSO shifts the regions of storm activity and frequency in the
eastern and northwest Pacific and decreases the frequency of storms
during the warm phase of ENSO in the North Atlantic region
(Henderson-Sellers et al., 1998).
Risk of waterborne infectious diseases and vector-borne diseases
also is likely to be influenced by climatic changes and ENSO events
as discussed in Chapter 2 of this report. In addition, there is a
risk of increased morbidity and mortality among vulnerable
populations if global warming disrupts normal weather patterns and
causes temperature extremes (hot or cold waves), regional flooding,
and severe storms. In some areas, however, climate change may
result in milder weather patterns, resulting in lower morbidity and
mortality. Some of these health concerns, as well as the effects of
climate change on marine ecosystems, have been addressed by the
collection of marine disturbance event data in the HEED program
(Box 1-1).
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BOX 1-1 Health, Ecological and Economic Dimensions of Global
Change Program (HEED)
In the final session of the Workshop on the Ocean's Role in
Human Health, Ben Sherman and Erika Siegfried from the Harvard
School of Public Health gave a presentation on the Health,
Ecological and Economic Dimensions of Global Change Program (HEED).
This three-year effort ending in 1998, was funded by NOAA's Global
Programs and NASA and began the effort to develop a systematic
methodology for collecting morbidity and mortality occurrence data
across a range of marine species. The goal was to provide a
baseline level of historic data on major marine ecological
disturbance events to better understand and recognize changes as
they occur in the world's oceans. HEED attempted to bring together
the expertise of different disciplines, organize historical data in
a standard format, assess the integrity and coverage of data and
provide a method for standardization of data collection and
analysis for the future. The resulting database was designed to be
used to map reports of ecological disturbances to reveal geographic
and temporal "hotspots." The occurrence of "hotspots" could serve
as indicators of the impacts of climate variability such as an El
Niño event. In establishing databases of this type the
information entered must be independent of hypothetical outcomes.
It is not possible to predict what types of queries will yield the
most valuable correlations, thus it is important to assure the
quality and comprehensiveness of the data collected.
The rise in sea level, estimated at 1.2–2 cm per decade
over the last century. threatens human health through the magnitude
of the storm surges that, even in the past, have had a devastating
effect in low lying countries like Bangladesh (NRC, 1998a). Sea
level rise results from the expansion of water as it warms, the
melting of polar ice, and the solid-Earth adjustment3 (rebounding from the weight of the
last glaciation). Sea level rise has already had a noticeable
effect on storm-surge occurrence at low-lying coasts and islands.
Because most of the non-oceanic water is stored in the polar ice
sheets, changes in the stability of these sheets could have a
significant impact on sea level (Nicholls et al., 1995). There has
been concern that the stability of the West Antarctic Ice Sheet is
vulnerable to global warming and may collapse, causing a
significant effect on global sea level. It is not yet possible to
predict the likelihood of collapse, but the stability of the West
Antarctic Ice Sheet is currently under intensive study. During the
winter of
3 The upward
or downward movement of the Earth's crust following the melting of
the ice sheets, which "unloaded" huge weight. Glacial rebound is
still being observed and has a major effect on observed sea
level.
Page 38
1997/98, the ice cover in the Weddell Sea was less than in any
winter since satellite observations began in the early 1970s.
Abrupt change in ocean circulation has been advanced as a
possible outcome of warming and increased fresh-water loading of
the high latitude oceans (Broecker, 1997; Manabe and Stouffer,
1994; Rahmstorff, 1995). The great meridional overturning
circulation described at the start of this chapter is thought to
have been stable over the past 1000 years. Paleoclimate studies
show that it was greatly altered in intensity and depth
distribution during the last glacial period, and suffered frequent
oscillations during other glacial periods. Computer models of the
coupled ocean/atmosphere/land system suggest that we may now be
entering a period of instability. Although still very speculative,
such events could lead to dramatic changes in the climates of
northern Europe and the Middle East over time-scales of 10 to 50
years.
The Importance of Preparedness of the
Health Services
The most effective way to reduce the immediate cost in lives and
human suffering from a natural disaster caused by a shift in
weather patterns as occurs during an El Niño, is to improve
the promptness and quality of the response of health and medical
services. Coastal areas subject to surges, tropical storms, or
tsunamis require a higher level of preparedness of both the
emergency medical services and the health sector at large. Time and
money invested on hospital contingency planning, simulation
exercises, and training, not only of the first responders, but also
of the entire health services, should ameliorate the outcome of
ocean-driven disasters. Evidence for such progress may be seen in
the recent response to the 1997/1998 El Niño. Although the
actual health impact is still being evaluated by the affected
countries and compiled at the international level by the Pan
American Health Organization (PAHO)/World Health Organization
(WHO), it is striking to note the sharp decrease in international
appeals by Latin American countries compared to the 1982/83 El
Niño. This suggests an improvement in the local response, a
result of 20 years of increased national health preparedness and
training.
Scientifically accurate and timely forecasting alone will not
prevent high death tolls or decrease damages, unless the warning is
transmitted, disseminated, and acted upon locally. The last
decades' cyclones in the Indian subcontinent were marked by
unnecessary loss of lives due to unheeded alarm. Apparently, part
of the population either did not receive or fully appreciate the
official warning and in other instances the design of the shelters
did not accommodate the cultural norms of the community, i.e., did
not include dividing walls to separate men and women (Talukder et
al., 1992). Finally, even improved predictions and effective
reporting are useless if no evacuation plans are available. The
lower mortality associated with hurricanes on the coasts of the
United States in the last 30 years is the result of several
factors: improved warning systems, compliance
Page 39
with more stringent building codes, a successful policy of
massive evacuation in the event of a serious storm, and fewer
landfalling hurricanes (Pielke and Pielke, 1997).
Gradual climatic changes and the possible and widely anticipated
impact on disease transmission require approaches other than the
traditional disaster planning aimed at improving medical readiness.
Operational research on the cost effectiveness of surveillance
techniques and control measures are needed to monitor and respond
to disease outbreaks, natural disasters, such as floods and storms,
and heat waves. Malaria, dengue, and cholera are increasing
pandemics, regardless of any causal effect of the El Niño,
and even the known effective control measures have yet to be
implemented. Protection of the population in the United States and
other developed countries in the event of climatic disturbances
requires a frontal and decisive reduction of the transmission in
developing countries as well. The problem is global, therefore the
solution must involve the cooperation of the international
community.
New Technologies for Ocean
Environmental Observation
Physical Oceanography/Meteorology
As the problems facing life on Earth multiply, our ability to
monitor them is also increasing rapidly. There has been a rapid
increase in technological capacity, but a lag in implementation of
these new tools. Improvements in our understanding of ocean
processes will depend on a greater commitment to using new
technologies to improve the baseline data used in constructing and
calibrating models. Some of the current projects in ocean
observations are described below.
Thanks to solid-state electronics, a large family of drifting
and moored sensor packages is now at work monitoring the
3-dimensional ocean: its velocity, movement of fluid particles,
temperature, salinity, and dissolved oxygen. PALACE floats, for
example, now roam the ocean by the hundreds, drifting with water
masses at great depth, and rising periodically to the surface to
transmit their data to a satellite. The 3-dimensional ocean, with
its patchy, laminated structures of biology, chemistry, and physics
can now be monitored by drifting and moored sensors, and monitored
from space using remote sensing. The launch of SeaWiFS in August
1997 gives us the first satellite dedicated to the global imaging
of oceanic surface biological activity since the loss of the
Coastal Zone Color Scanner in 1986. Comprehensive monitoring of
coastal pollution and global primary productivity is now possible.
Tracking of tropical cyclones and prediction of their path and
intensity is vastly improved by satellite imagery, infrared images
showing the sea-surface temperature, and the altimetric
measurements of the Ocean Surface Topography Experiment
(TOPEX)-Poseidon satellite, which measure the background surface
currents of the ocean. The new network of long-range
Page 40
Doppler radars of the U.S. weather service aids in this process
as storms approach the coast.
Integration of these new observations into computer models of
the ocean and atmosphere improves both predictions and
understanding of the underlying dynamics of the system. The nearly
exponential increase in computing power over recent decades gives
us tools that may soon resolve processes of moderate
scale—like regional plankton blooms—within the context of
a global model of the coupled ocean/atmosphere. However, a recent
NRC report has identified a lack of available computing resources
for the testing and application of climate models (NRC, 1998b).
Chemical and Biological Sensors
Biological and medical research is rapidly improving our ability
to make rapid measurements of chemical and biological substances in
fluids. This technology, applied to environmental measurements of
the ocean, will give us high resolution 3-dimensional maps of key
biological and chemical components over time. Although this
technology can be prohibitively expensive, transfers of medical
technologies developed for blood analysis to marine applications
are feasible. In the past, only dissolved oxygen and salinity
measurements have been widely collected by small electronic
sensors. However, now there is active development of sensors for
dissolved CO2 (to better than 1
PPM4) and nutrients, which in the
past required elaborate analysis of retrieved water samples.
Biological monitoring with fluorometers and light-transmission
sensors has been possible for some time, but new "bioprobes" for a
wide range of substances are being developed aggressively.
Fiber-optic chemical sensors can detect a range of variables in
extremely small fluid samples (organic vapors, dissolved oxygen,
CO2, and pH; Ferguson et al., 1997;
Tabacco et al., 1998). Methods for measuring specific complex
biological molecules are now under development.
One of the challenges in developing new instrumentation lies in
the special requirements of the ocean environment. In hospital
applications, sensors for blood pH, O2, and sugar must be replaced or
recalibrated on time scales of one day or less. This would be
impossible in the long term deployments typically used in
oceanographic research. A discussion of sensor development,
particularly those relating to oceanic carbon, is given in NRC
(1993).
Collection of data from the physical, chemical, and biological
monitoring systems described above creates a parallel need for
comprehensive, structured databases. The efficient utilization of
this information should be optimized by carefully designed,
query-driven retrieval systems.
4 PPM = Parts
per million.
Page 41
Conclusions
Marine natural disasters present challenges to both public
health officials and scientists who must work together to minimize
the impact of these events on human health. In some cases, this
involves implementing existing technologies and preventive measures
that have proven capacity to reduce human suffering. However, it is
still impossible to predict and prepare for all emergencies as the
recent tsunami in New Guinea and Hurricane Mitch in Central America
have demonstrated. Furthermore, there are indications that the
global climate is changing, affecting weather and the ocean alike.
Change is nonlinear—its individual components interact in
surprising ways. When human interventions occur on a back-drop of
global climate change, the net effects become all the more complex
and difficult to predict. The implications of the current warming
trend are controversial, but this in itself argues for vigilance in
monitoring changes in physical and biological systems so that
predictions can be improved and problems can be identified before
they become emergencies.
Potential strategies for the future include programs for public
health and scientific monitoring for climate change and the health
effects of climate change.
1. Support for international ocean research programs. Programs
such as CLIVAR (Climate Variability and Predictability Programme)
and GOOS (Global Ocean Observing System) help meet some of the
needs for global monitoring. GOOS, for example, has a major
initiative called "Health of the Oceans," which examines the
coastal ocean and human health.
2. Closer cooperation and exchange of information across
borders. Improved communication between emergency and disaster
coordinators in the Western Hemisphere can help to identify common
problems and solutions. In this area, the efforts of the PAHO/WHO
to establish Internet links among professionals in the Americas
need to be strengthened and expanded.
3. Emphasis on improving the public health infrastructure. In
developing countries, storm resistant health facilities would
improve medical and hospital disaster preparedness. Contingency
planning and training also improve preparedness as well as support
for the adoption of strict standards for hurricane and flood
resistance. This emphasis on preventative measures to reduce the
impacts of disasters was recognized by the Scientific and Technical
Committee convened by the International Decade of Natural Disaster
Reduction in June, 1998 at the World Bank in Washington, D.C.
(PAHO, 1998c).
4. Establish baseline observations of the physical ocean and its
ecosystems to monitor global change. Change can only be evaluated
in the context of past experience. Therefore, our ability to
understand future events will depend on the quality of the
observations and analyses of that are collected now. This will
require the implementation of newly developed technologies and the
establishment of databases to design and evaluate models.
Page 42
The next decade will be a crucial period for monitoring climate.
The uncertain predictions of climate models will be tested and the
changes in the environment may be more striking and heterogeneous
than currently predicted. Achievement of the above recommendations
will require a cooperative effort among the social, political, and
economic sectors of the community, both local and internationally;
potentially through close coordination between the scientific
community and various local and international agencies such as the
U.S. Agency for International Development and PAHO/WHO.