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Coral Bleaching, Coral Mortality, and Global Climate Change Report presented by Rafe Pomerance, Deputy Assistant Secretary of State for the Environment and Development To the U.S. Coral Reef Task Force, 5 March 1999, Maui, Hawaii

Released by the Bureau of Oceans and International Environmental and Scientific Affairs U.S. Department of State, March 5, 1999

EXECUTIVE SUMMARY

In the 1970s climatologists began to warn that the Earth would experience rapid changes, induced in part by emissions of "greenhouse" gases resulting from the burning of fossil fuels, intensifying land use, and reduction in forest cover. They projected that: 1) ocean and air temperatures would rise significantly in the coming decades; 2) biological systems especially sensitive to temperature would be the first to suffer losses; 3) individual (physiological) and systemic (ecological) thresholds would be crossed; and 4) at this point, the losses may be difficult to reverse.

Coral reefs are projected to be among the most sensitive ecosystems to long-term climate change. Corals are especially sensitive to elevated sea surface temperatures. When physiologically stressed, corals may lose much of the their symbiotic algae, which supply nutrients and color. In this state corals appear white and are referred to as "bleached." Corals can recover from short-term bleaching. However, prolonged bleaching can cause irreversible damage and subsequent mortality.

Due to their structural complexity, corals are one of the most productive ecosystems on Earth. As a consequence, they provide many services, including fisheries, coastal protection, tourism, and medicines. Despite their readily apparent value, approximately 58% percent of the world's reefs may already be threatened by human activities such as coastal development and overexploitation of marine products.

In 1998 coral reefs around the world appear to have suffered the most extensive and severe bleaching and subsequent mortality in modern record. In the same year, tropical sea surface temperatures were the highest in modern record, topping off a fifty year trend for some tropical oceans. These events cannot be accounted for by localized stressors or natural variability alone. Nor can El Niño by itself explain the patterns observed worldwide. Rather, the impact of these factors was likely accentuated by an underlying global cause. Thus the geographic extent, increasing frequency, and regional severity of mass bleaching events are likely a consequence of a steadily rising baseline of marine temperatures, driven by anthropogenic global warming.

Based on early reports, the repercussions of the 1998 mass bleaching and mortality events will be far reaching in time and through space. Even under the best of conditions, many of these coral reef ecosystems will need decades to recover. In the meantime, human populations dependent on reef services face losses of marine biodiversity, fisheries, and shoreline protection.

Trends of the past century suggest that coral bleaching events may become more frequent and severe as the climate continues to warm, exposing coral reefs to an increasingly hostile environment. This global threat to corals compounds the impacts of more localized anthropogenic factors that already place reefs at risk.

Significant attention needs to be given to the monitoring of coral reef ecosystems, research on the projected and realized impacts of global climate change, and measures to curtail greenhouse gas emissions. For, even those reefs granted well-enforced legal protection as marine sanctuaries, or as areas managed for sustainable use, are threatened by global climate change.

BACKGROUND

Many species of plants and animals are very sensitive to climate. As climate patterns change, so do the locations of species. They must track the climate regimes appropriate for their survival, or face extinction. In the 1970s climatologists began to warn that the Earth would experience rapid changes, induced in part by emissions of "greenhouse" gases resulting from the burning of fossil fuels, intensifying land use, and reduction in forest cover. They projected that global temperatures would rise significantly in the coming decades (e.g., Climate Resource Board, 1979). Scientists projected that species might respond concurrently; ranges might shift, natural communities might be disrupted, and mass extinction of some species might occur (Peters, 1988).

CORAL REEF ECOSYSTEMS

Coral reefs are projected to be among the most sensitive ecosystems to long-term climate change (IPCC, 1998). Corals are small animals. Most live in immense colonies, harvesting nourishment and energy from microscopic algae (plants called zooxanthellae) which inhabit their cells by the thousands (Goreau and Goreau, 1960; Muscatine, 1973). The algae are golden brown and combine with other pigments to lend their coral hosts (which largely have transparent tissues) a spectacular appearance (Kleppel et al., 1989).

Coral and algae work cooperatively to generate limestone skeletons. Over hundreds of years, the limestone skeletons accumulate to form the framework and support structure of a coral reef. Innumerable animals and plants settle, attach, and burrow into the structure, creating a diverse and dynamic ecological community. Because this process is temperature dependent (sea surface temperatures of 64 degrees F or more), coral reefs are essentially tropical (roughly 20 degrees north to 20 degrees south latitude from the equator). However, reefs are also found outside the tropics where warm currents bring tropical waters into higher latitudes (Japan, South Africa, and Bermuda for example). Within the tropics, the best developed reefs in terms of coral cover are in the Western Pacific, the Indian Ocean, and the Caribbean. The reefs of Indonesia, Philippines, and Papua New Guinea are among the most species rich. Due to the circulation and upwelling of cold water currents, coral reefs are rare on the Pacific Coast of the Americas and the Atlantic coast of Africa (Stafford-Deitsch, 1993). While it has long been known that low temperatures limit the existence of coral reefs, it has only recently been appreciated that corals have upper temperature thresholds (Goreau et al., 1997; Strong et al., 1997; Glynn, 1996; Gleeson and Strong, 1995; Montgomery and Strong, 1994; Glynn and D'Croz, 1990; Jokiel and Coles, 1990).

According to a recent study (Bryant et al., 1998), fifty-eight percent of the world's coral reefs are potentially threatened by human activity. Almost a half billion people, eight percent of the total global population, live within 100 kilometers of coral reefs. Overexploitation and coastal development pose the greatest threats, with destructive fishing practices, marine pollution, and runoff from inland deforestation and farming also placing reefs at risk.

THE VALUE OF CORAL REEFS

Corals are one of the most productive ecosystems on Earth (Grigg et al., 1984). Much of the productivity derives from the substantial concentration of marine biodiversity in coral reefs. The coral reef is the most complex, species-rich, and productive marine ecosystem (Bryant et al., 1998; Stafford-Deitsch, 1993). One estimate (Reaka-Kudla, 1996) proposes that coral reefs have about 1 million species, with only 10% percent described. Large species of fish and other organisms typically school along the reef, while small ones pack into the extensive network of crevices. The benefit from coral reef services is both immediate and long-term, making them a priority for conservation and a major resource for sustainable development.

• Tourism. Where coral reefs exist, substantial income can be derived from tourism. People from all over the world travel to reefs to snorkel, dive, fish, and bask on the coral sands. Most island populations in the Pacific and Indian Oceans, as well as the Caribbean, are dependent on income derived from tourism. In 1990 alone, reef and beach-based tourism added $89 billion to the gross development product (GDP) of the Caribbean region (Jameson et al., 1995). Tourism on the Great Barrier Reef generates 1.5 billion dollars each year for Queensland, Australia (Done et al., 1996; Richmond, 1993). Florida's reefs bring in approximately 1.6 billion dollars annually (Birkeland, 1997).
  
  
• Fisheries. Most of the world's poor are located within the coastal zones of developing regions, and depend directly on reef species to meet their protein needs (Bryant et al., 1998). Although reefs cover less than 0.2% of the ocean's area, they contain 25% of marine fish species (Roberts et al., 1998). Fish shelter in reefs, and use them as feeding, spawning and nursery grounds. Coral reef fisheries yield at least 6 million metric tons of fish catches around the world annually, excluding local sustenance fisheries (Munro, 1996). Reefs provide one-quarter of the fish catch in developing countries and employment for millions of fishers (Roberts et al., 1998). Reef damage off the Philippines has already been blamed for fisheries losses totaling more than $80 million per year and the elimination of 127,000 jobs (McAllister, 1988).
  
  
• Mainland and Island Protection. The protective services provided by reefs reduce storm damage, coastal erosion and flooding by intense wave action. Over geologic time, coral reefs have enabled the formation of lagoons and calm shorelines where seagrass beds and mangroves can flourish, providing habitat for numerous species at the interface of land and sea (Bryant et al., 1998; Baskin, 1997).
  
  
• Medicine. About half of the potential pharmaceuticals being explored are from the oceans, many from coral reef ecosystems (see reviews by Fenical, 1996; Hay and Fenical, 1996). Several promising drugs have already been identified, developed, and tested (Carte, 1996).
  
  
• Ecological Indicators. Due to the potential vulnerability of modern corals to high temperature, coral reefs may be among the first systems to show signs of ecological stress from global warming (IPCC, 1998). Detecting this change will require an extensive network of monitoring sites throughout the coral reef regions of the world.

PATHWAY TO CORAL BLEACHING AND DEATH

When corals are physiologically stressed, the critical balance that maintains their symbiotic relationship with algae is lost. The coral may lose some or most of their algae, a major source of nutrition and color. In this condition, corals are referred to as "bleached." In some species, tissue growth is halted, skeletal accretion is stopped (Goreau and Macfarlane, 1990; Leder et al., 1991), and sexual reproduction is suspended (Szmant and Grassman, 1990). Corals survive if the stress is brief, but will die if it is prolonged (Wilkinson et al., 1999; Glynn, 1996). However, even a sublethal stress may make corals highly susceptible to infection by a variety of opportunistic pathogens. Disease outbreaks (epizootics) may result in significant coral mortality (Hayes and Goreau, 1998).

Once mortality occurs, the coral's soft tissue becomes a food source for scavengers, making the increasingly bare skeleton a feasible site of attachment for rapidly growing seaweeds and other opportunistic organisms (Hayes and Goreau, 1998). As long as the structure of coral reefs is maintained, they offer protection to a wide variety of marine life. If favorable conditions return and are sustained, coral larvae may settle on the reef structure, renewing the reef building process. However, in many cases, where large populations of sea urchins, parrot fish, and worms erode the dead reef skeleton (Wilkinson et al., 1999; Eakin, 1996; Reaka-Kudla et al., 1996; Glynn, 1988; Hutchings, 1986; Ogden, 1977), the reef becomes vulnerable to destruction by storm surges. Once the reef is reduced to rubble, fish and other marine organisms are no longer supported. Local human populations are thus placed at risk; over time fisheries stocks are greatly diminished, shoreline erosion increases, and the tourist industry is likely to suffer (Wilkinson et al., 1999; Roberts et al., 1998; McAllister, 1988).

Coral bleaching is most often associated with a significant rise in sea surface temperatures (Brown, 1997; Glynn, 1996; Goreau et al., 1993; Glynn, 1991; Cook et al., 1990; Gates, 1990; Jockiel and Coles, 1990; Hoegh-Guldberg and Smith, 1989; Jaap, 1985; Fankboner and Reid, 1981). On site observations and National Oceanic and Atmospheric Administration (NOAA) satellite-derived sea surface temperature records from North Atlantic and Caribbean reef locations show a significant correlation between all large-scale bleaching events and high sea surface temperatures (Strong et al., 1998; Gleeson and Strong, 1995; Goreau et al., 1993). Water temperatures of even one degree Celsius above normal summer maxima (hereafter "hot spot" [note 1]), lasting for at least two or three days appear to provide a potentially useful predictor of consequent bleaching (Goreau and Hayes, 1994). While there are differences in response among species and populations, most coral are likely to bleach but survive if temperature anomalies persist for less than a month, enabling corals to recover. However, the chronic stress of sustained high temperatures can cause physiological damage that may be irreversible (Wilkinson et al., 1999).

It appears that coral reefs are bathed in unusually warm waters through at least two non-exclusive, mechanisms:

• Doldrum conditions. Weather patterns typified by clear skies and slight or still wind or waves result in little or no movement and mixing of warm and cold waters. Under these conditions, solar radiation warms surface and shallow waters (particularly during the summer when the sun is overhead).
  
  
• Current transport. Ocean currents transport "pools" of warm water, sometimes delivering them to reef regions. These warm waters can linger for months before moving on or dissipating.

Stress-related bleaching can also be induced if corals are subjected to a reduction of marine salinity, intense solar radiation (especially ultraviolet wavelengths), exposure to the air (by low tides or low sea level), sedimentation, or xenobiotics (chemical contaminants such as copper, herbicides, and oil) (see reviews in Brown, 1997; Glynn, 1996). Often, these conditions are at least an indirect consequence of extremes in weather (such as hurricanes and typhoons) which may be proceeded by or occur concurrently with elevated sea surface temperatures. As a consequence, multiple factors may act in concert to cause bleaching. High solar irradiance (particularly ultraviolet wavelengths) is thought to be especially stressful to corals when coupled with elevated sea surface temperatures (Glynn, 1996).

CORAL REEF BLEACHING AND MORTALITY TRENDS

Nearly 80 years ago Alfred Mayer described coral bleaching as a natural event. He observed the phenomenon on a small scale, such as in overheated tide pools (Goreau and Hayes, 1994). Because the events were rare, localized, and corals typically recovered, bleaching events caused little concern (Hayes and Goreau, 1991; Hayes and Bush, 1990). However, in the early to mid 1980s coral reefs around the world began to experience large scale bleaching (Brown, 1997; Glynn, 1996; Goreau, 1992; Glynn, 1991; Hayes and Goreau, 1991; Goenaga and Canals, 1990; Goreau, 1990; Jokiel and Coles, 1990; Williams and Bunkley-Williams, 1990). Since then, such events have taken place almost every year [note 2], at one time or another impacting every reef region of the world, and across all depths of the tropical reef (Wilkinson et al., 1999; Hayes and Goreau, 1991).

The events of 1987 and 1990 were sufficiently alarming (each unprecedented in global scale and severity) that hearings were held before the U.S. Senate. [note 3] Witnesses at the hearing confirmed that the frequency and extent of coral bleaching represented a severe threat to coral survival and reef preservation (Hayes et al., 1990). Furthermore, they affirmed that there was sufficiently strong evidence to suggest that tropical corals may be responding to trends in global warming (Goreau, 1990; Hayes et al., 1990).

Although highly spatially variable, the coral bleaching of 1998 is the most geographically extensive and severe in recorded history (Wilkinson et al., 1999; ISRS, 1998; ITMEMS, 1998; Strong et al., 1998). Coral bleaching was reported in at least 60 countries and island nations by observers at sites in the Pacific Ocean, Indian Ocean, Red Sea, Persian Gulf, and the Caribbean. Only the Central Pacific region seems to have been spared. Unlike most previous bleaching events, which were most severe at depths less than 15 m, the impact of the 1998 event extended to depths as great as 50 m (Wilkinson et al., 1999; ITMEMS, 1998; Wilkinson, 1998). In these areas, virtually all species of hard and soft corals, as well as many other zooxanthelate invertebrates (e.g., giant clams), suffered bleaching (Wilkinson et al., 1999; ISRS, 1998; ITMEMS, 1998).

The severity of the coral bleaching ranged from catastrophic, resulting in mass mortality throughout at least eighty percent of a reef system (i.e. affecting the whole colony), to negligible in cases where only small patches of reef bleached and then recovered (Wilkinson et al., 1999; Wilkinson, 1998). This variation likely reflects differences in genetically-based species- and population-specific responses (Buddemeier and Fautin, 1993), the location of the reef (e.g., depth), strength of the stressor(s) involved, and the duration of the stress (Wilkinson, 1998).

Preliminary assessments indicate that the Indian Ocean is the most severely impacted region, with devastating coral mortality. Greater than seventy percent mortality has been observed off the coasts of such regions as Kenya, the Maldives, the Andamans, and the Lakshadweep Islands. About seventy-five percent of the corals have been reported to be dead in the Seychelles Marine Park System and at least eighty percent in the Mafia Marine Park (Wilkinson et al., 1999).

A complete assessment of the ramifications of the 1998 mass bleaching event will require several years of investigation. Undoubtedly, some corals will recover, and perhaps even become inhabited by more stress tolerant algae (Buddemeier and Fautin, 1993). However, other corals may have endured such significant physiological and metabolic stress that they will be more susceptible to the impacts of future stress events (Wilkinson et al., 1999). Thus, episodes of coral morbidity and mortality may follow, consequences of the primary insults of bleaching.

GLOBAL CLIMATE TRENDS

In some regions, local and regional stressors (e.g., sedimentation, pollution, low tides, and salinity) undoubtedly contributed to the coral bleaching events of 1998 (Wilkinson et al., 1999). However, anomalously high sea surface temperatures closely preceded and/or correlated with reports of mass coral bleaching worldwide (Wilkinson et al., 1999; Strong et al., 1998). Combined land-air and sea surface temperatures make 1998 the warmest year of the century (NOAA, 1998a), with both the land and sea surfaces setting record high anomalies (NOAA, 1999). Anomalously warm temperatures were found throughout the tropics in 1998 (NOAA, 1999). Tropical sea surface temperatures were the highest in the modern record, and the HotSpots of the world's tropical oceans were more extensive in the first six months of 1998 than for any previous year (Strong et al., 1998).

While there is considerable support for the hypothesis that anomalously high sea surface temperatures have caused the recent episodes of mass coral bleaching and mortality, the specific mechanism(s) driving the rise in sea surface temperatures remain uncertain and thus controversial (Wilkinson et al., 1999). Three predominant theories, representing potentially interacting scenarios, have emerged: 1) stochasticity and chaos, 2) El Niño and other variations in climate, and 3) global warming.

Stochasticity and Chaos. At any location, variations in weather across both short and long term time scales can be large and are often unpredictable (Shukla, 1998; Lorenz, 1963). Natural climate variability, resulting both from internal fluctuations and from external causes (e.g., solar variability), provides the "background" against which all anthropogenic climate change is measured (IPCC, 1996). Many factors (e.g., wind direction and speed, rates of upwelling, days of cloud cover) that contribute to "bleaching conditions" seem to be naturally variable. While a statistical analysis has not yet been performed, the chance that all of the 1998 bleaching events occurred as a result of independent local causes, or random weather events, seems highly improbable.

El Niño and other natural variations in climate. By some measures, the 1997-1998 El Niño [note 4] was the strongest on record. This may be due, at least in part, to it being superimposed upon naturally occurring decadal time-scale fluctuations [note 5] (Kerr, 1999; McPhaden, 1999) and anthropogenic global warming (Trenberth, 1998). In many parts of the Pacific, the El Niño appears to be a significant factor contributing to severe coral bleaching events. It may also influence bleaching in the Caribbean Sea and Atlantic Ocean by changes in atmospheric circulation through the El Niño influences on global climate patterns (Coffroth et al., 1990). However, connections between El Niño and coral bleaching are not apparent for all Pacific locations. Furthermore, it is less clear how El Niño influences high sea surface temperature anomalies in the Indian Ocean and Arabian Gulf (Wilkinson et al., 1999; ISRS, 1998). At this time, it appears that El Niño, by itself, cannot account for the extreme warmth of 1998 but is part of a larger climate pattern that influenced temperatures across the tropical Indian and Pacific Oceans (NASA, 1999). However, it should be noted that the 1983, 1987, and 1998 mass coral bleaching events corresponded with record El Niños, and the high sea surface temperatures diminished as the El Niños dissipated (Wilkinson et al., 1999).

Global Climate Change. Over much of the world, temperatures in 1998 topped off warming trends, and were the warmest in at least 600 years (Mann et al., 1998), as far back as global estimates of climate can be made. Globally, average surface air temperatures are about 0.5 degree C (almost 1 degree F) higher than average temperatures in the 19th century (NOAA, 1997). In 1996 the IPCC had already concluded that global warming is measurable at about 0.3 to 0.6 degree C (IPCC, 1996), and since then 1997 and 1998 have each been warmer than any previous year. Analyses by the National Atmospheric and Space Administration (NASA) indicate that the rate of warming is the most rapid of any previous period of equal length in the time of instrumental records (NASA, 1999). For some of the tropical oceans significant increases in sea surface temperature have been observed over the last 50 years. Detailed analysis of the temperature records from all coral reef sites shows that in most Northern Hemisphere locations tropical seas have been warming faster than the global average over the past 17 years (Strong, personal communication). The IPCC (1996, 1998) states that anthropogenic activities (esp., burning of fossil fuels, changes in land use, and reduction in forest cover) are increasing the atmospheric concentrations of greenhouse gases (e.g., carbon dioxide), altering radiative balances and warming the atmosphere. Still, it should be noted that there are strong regional differences in warming rates and average sea surface temperatures in the Southern Hemisphere sites have been showing either no increase or even cooling (NOAA, 1999; Wilkinson et al., 1999).

FUTURE SCENARIOS

Complete recovery of reefs is dependent on numerous factors, including local severity and duration of thermal stress, species specific sensitivity and growth rates, fragmentation of remaining coral reefs, and recruitment of coral larvae in the area, as well as timing and severity of additional stresses (Done, 1999; Wilkinson et al., 1999; ISRS, 1998). While coral reefs damaged by acute, local stresses such as ship groundings, hurricanes, or pest outbreaks can recover in a few decades as long as surrounding reefs are healthy, evidence suggests that restoration following chronic, widespread stresses will be much slower (Wilkinson et al., 1999; IPCC, 1998). A percentage of corals have always survived the mass extinctions brought on by natural climatic variabilities in the past (e.g., 75,000 years ago). However, due to the potential rate at which significant climatic changes could now proceed, the ability of most corals to acclimatize and/or migrate is uncertain.

At locations where coral mortality was catastrophic to severe in 1998, there will be fewer corals of the affected species reproducing in coming years, and hence a much reduced supply of new coral larvae (Wilkinson et al., 1999). Even if there were an adequate supply of coral larvae, reef recovery will be hindered around many populated shores by pollution from sewage, soil erosion, fertilizers, overfishing, and physical damage. Recent increases in incidents of coral disease have further reduced numbers of some important reef building corals such as the Acropora (Bryant et al., 1998), which are being considered for listing under the Endangered Species Act.

Global climate change poses an increasing threat to coral reefs regardless of its contribution to date. An increase in carbon dioxide (CO2) in the atmosphere can reduce the ability of corals to form limestone skeletons, slowing their growth and making them fragile (Done, 1999). Global mean sea-surface temperatures are projected to increase approximately 1-2 degrees C by the year 2100 (NOAA, 1998b). If the frequency of high-temperature episodes increases as mean temperature gradually rises, corals will experience more frequent and widespread disturbances (Done, 1999; IPCC, 1998). Hot spot zones would become even more widespread in area and last longer (Strong et al., 1998; Goreau and Hayes, 1994). Furthermore, these thermal effects are projected to coincide with sea level rise, more frequent tropical storms and El Niños, and consequently greater coastal erosion, turbidity, and sedimentation in many reef locations (IPCC, 1998). Stressed by any of these factors, the ability of coral reefs to withstand high waves and recover from breakage or bleaching events may be significantly reduced (Done, 1999).

CONCLUSION

The mass coral bleaching and mortality events of 1998 cannot be accounted for by localized stressors or natural variability alone. Nor can El Niño by itself explain the patterns observed worldwide. Rather, the impact of these factors was likely accentuated by an underlying global cause. At this time, it appears that only anthropogenic global warming could have induced such extensive coral bleaching simultaneously throughout the disparate reef regions of the world. Thus the geographic extent, increasing frequency, and regional severity of mass bleaching events are likely a consequence of a steadily rising baseline of marine temperatures.

Based on early reports, the repercussions of the 1998 mass bleaching and mortality events will be far reaching in time and through space. Even under the best of conditions, these coral reef ecosystems will need decades to recover. In the meantime, human populations dependent on reef services face losses of marine biodiversity, fisheries, and shoreline protection (Wilkinson et al., 1999; Bryant et al., 1998; Goreau and Hayes, 1994).

Trends of the past century suggest that coral bleaching events may become more frequent and severe as the climate continues to warm, exposing coral reefs to an increasingly hostile environment. Furthermore, they imply that any strategy to maintain coral reefs must include reduction of greenhouse gas emissions. For, even those reefs granted well-enforced legal protection as marine sanctuaries, or as areas for sustainable use, are threatened by global climate change.

RECOMMENDATIONS

Immediate action should be taken to minimize stress to tropical marine ecosystems:

• stabilize and reduce greenhouse gas emissions
  
• preserve the physical integrity of the marine environment
  
• reduce sediment, chemical, and solid waste contamination of marine waters

To be most effective as early and sensitive warning signals of global climate change, coral reef bleaching events must be monitored on site and through remote sensing, and investigated and reported upon by the scientific community. In order to best inform future decisions, the research findings must then be translated effectively into public policy and communicated to funding agencies and the public.

A. Monitoring

• Improve and increase information resulting from remote sensing technologies.
  
• Support satellite-based monitoring of sea surface temperature change through the "HotSpots" early warning program.
  
• Expand and coordinate international rapid response teams and long term monitoring to measure bleaching and mortality.
  
• Support the Global Coral Reef Monitoring Network (GCRMN) and associated regional networks, expanding the network as resources permit.

B. Scientific Research

• Establish better baseline data (biological, climatic, and socioeconomic).
  
• Coordinate multidisciplinary research programs that investigate the relationship between large-scale coral bleaching/mortality events and global climate change.
  
• Coordinate targeted research programs that investigate the long-term effects of coral bleaching and mortality on ecological, social, and economic systems.
  
• Coordinate research programs that investigate the physiological tolerance and adaptation capacity of corals to acute and chronic stressors.
  
• Develop dynamic, predictive models of climate and ecological process, as well as socio-economic factors.
  
• Coordinate these research programs internationally through bilateral and multilateral programs and instruments.

C. Policy

• Emphasize and appreciate that coral reefs can be monitored as a useful bioindicator of environmental stress.
  
• Work within the Framework Convention on Climate Change to identify additional ecosystems especially sensitive to climate change and require their monitoring for climatically-induced damage.
  
• Apply the lessons learned from the 1998 mass coral bleaching event to the next stages of climate policy, while implementing current commitments to reduce greenhouse gases emissions
  
• Develop an integrated strategy to address this issue through the United Nations system, as well as through other international programs and treaties.

D. Communication

• Develop a communication strategy to address diverse political and public needs such as (a) internationally, address concerns of small island states, and (b) address concerns of the general public.

Substantial financial support is needed to put these priorities into practice. Because the issues of climate change are global and long-term in scale, governments around the world need to work together to make available the funds that will enable these important initiatives.

Acknowledgements

This document was drafted by Rafe Pomerance, Jamie K. Reaser, and Peter O. Thomas. We are especially grateful to Al Strong, Ray Hayes, and Tom Goreau for bringing the breadth and gravity of these events to our attention and providing extensive assistance in document preparation. Thanks to D. James Baker for the support of NOAA which contributed much of the information critical to this paper. The following individuals reviewed the document and offered constructive feedback: Barbara Best, Andy Bruckner, Mark Eakin, Ann Kinzig, John Ogden, Michael Oppenheimer, Arthur Paterson, Tony Socci, and Kevin Trenberth. Donald McAllister and Clive Wilkinson generously shared their original work.

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ENDNOTES

1/ NOAA monitors satellite-derived observations of sea surface temperature to detect rises of one degree Celsius above what is believed to be coral's maximum summertime temperature threshold. They then announce the locations of such "hot spots" in an effort to forecast coral bleaching events. Http://psbsgi1.nesdis.noaa.gov:8080/PSB/EPS/SST/climohot.html.

2/ The only exception occurred during the two years after the 1991 eruption of Mount Pinatubo in the Philippines. A fine aerosol haze was released into the upper atmosphere, reflecting sunlight back into space, resulting in the cooling of land and ocean surfaces, especially in the tropics.

3/ 27 November 1987, U.S. Senate Committee on Appropriations; 11 October 1990, U.S. Senate Committee on Commerce, Science, and Transportation.

4/ The El Niño Southern Oscillation (ENSO) is a natural oscillation of the coupled ocean-atmosphere system in the tropical Pacific. It has an important influence on climate and weather throughout the globe. The trade winds relax in the central and eastern Pacific reducing the upwelling of cold, nutrient rich waters. In the central and eastern Pacific, the result is a rise in sea surface temperatures and sea level. This further weakens the easterly trade winds and changes global atmospheric circulation. Weather patterns are disrupted in regions far removed from the tropical Pacific.

5/ Around 1977, a major increase in tropical Pacific Ocean temperatures, storm frequency, El Niños, and related climate patterns occurred. This appears as a regime shift (Trenberth and Hurrell, 1994), and may be associated with a change in the Pacific Decadal Oscillation (PDO), a warming phase in the Pacific having a period of 50-60 years (Mantua et al., 1997).

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