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2005 – a hot year
zx 2005 was the hottest year on average since the advent of reliable records in 1880.
zx That year exceeded the previous 9 record years, which have all been within the last
15 years.
zx 2005 also exceeded 1998 which previously held the record as the hottest year; there
were massive coral losses throughout the world in 1998.
zx Large areas of particularly warm surface waters developed in the Caribbean and
Tropical Atlantic during 2005. These were clearly visible in satellite images as
HotSpots.
zx The first HotSpot signs appeared in May, 2005 and rapidly expanded to cover the
northern Caribbean, Gulf of Mexico and the mid-Atlantic by August.
zx The HotSpots continued to expand and intensify until October, after which winter
conditions cooled the waters to near normal in November and December.
zx The excessive warm water resulted in large-scale temperature stress to Caribbean
corals.
2005 – a hurricane year
zx The 2005 hurricane year broke all records with 26 named storms, including 13
hurricanes.
zx In July, the unusually strong Hurricane Dennis struck Grenada, Cuba and Florida.
zx Hurricane Emily was even stronger, setting a record as the strongest hurricane to
strike the Caribbean before August.
zx Hurricane Katrina in August was the most devastating storm to hit the USA.
It caused massive damage around New Orleans.
Ex E c u t i v E Su m m a r y
Cl i v e Wi l k i n s o n a n d da v i d so u t e r
x
Status of Caribbean Coral Reefs after Bleaching and Hurricanes in 2005
zx Hurricane Rita, a Category 5 storm, passed through the Gulf of Mexico to strike
Texas and Louisiana in September.
zx Hurricane Wilma in October was the strongest Atlantic hurricane on record and
caused massive damage in Mexico, especially around Cozumel.
zx The hurricane season ended in December when tropical storm Zeta formed and
petered out in January.
zx Many of these hurricanes caused considerable damage to the reefs via wave action
and runoff of muddy, polluted freshwater.
zx The effects were not all bad. Some hurricanes reduced thermal stress by mixing
deeper cooler waters into surface waters.
zx Although there were many hurricanes, none passed through the Lesser Antilles to
cool the waters, where the largest HotSpot persisted.
2005 – a massive coral bleaching event
zx The warm water temperatures caused large-scale coral bleaching as a stress response
to the excessive temperatures.
zx Bleached corals were effectively starving and susceptible to other stresses including
diseases; many died as a result.
zx The first coral bleaching was reported from Brazil in the Southern Hemisphere; but
it was minor.
zx The first bleaching reports in the Caribbean were in June from Colombia in the
south and Puerto Rico in the north.
zx By July, bleaching reports came in from Belize, Mexico and the U.S. Virgin Islands
affecting between 25% and 45% of coral colonies.
zx By August, the bleaching extended to Florida, Puerto Rico, the Cayman Islands, the
northern Dutch Antilles (St. Maarten, Saba, St. Eustatius), the French West Indies
(Guadeloupe, Martinique, St. Barthelemy), Barbados and the north coasts of Jamaica
and Cuba.
zx Bleaching in these countries was generally severe affecting 50% to 95% of coral
colonies.
zx In some countries (e.g. Cayman Islands) it was the worst bleaching ever seen.
zx By September, bleaching affected the south coast of Jamaica and the Dominican
Republic, with 68% of corals affected;
zx By October, Trinidad and Tobago was reporting 85% bleaching, and the development
of a second HotSpot was causing the most severe bleaching for the last 25 years;
some places reported 100%, although it was highly variable between sites;
zx By November, minor bleaching also affected Venezuela, Guatemala and the Dutch
islands of Bonaire and Curacao, affecting 14% to 25% of corals.
zx In many countries (Cuba, Jamaica, Colombia, Florida, USA) there was great variation
in bleaching between sites. In Florida, areas exposed to regular large temperature
fluctuations, and nutrient and sediment loads were less affected. In the French West
Indies, the variation was attributed to different species composition between sites.
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Executive Summary
zx The corals vulnerable to bleaching were similar across the Caribbean, particularly:
Acropora palmata and A. cervicornis, Agaricia, Montastraea, Colpophyllia, Diploria,
Siderastrea, Porites, the hydrozoan Palythoa and the hydrocoral Millepora, which
has nearly disappeared from the French West Indies.
zx Bleaching persisted to mid-2006 in Guadeloupe, Martinique, Barbados and Trinidad
and Tobago, and, in 2007 in St. Barthelemy. Reefs in these countries showed few
signs of recovery, with between 14% and 33% of colonies still bleached.
2005 – extensive coral mortality and disease
zx The greatest damage occurred in the islands of the Lesser and Greater Antilles where
corals were bathed in abnormally warm waters for 4 to 6 months.
zx The greatest coral mortality occurred in the U.S. Virgin Islands, which suffered an
average decline of 51.5% due to bleaching and subsequent disease; the worst seen in
more than 40 years of observations.
zx Barbados experienced the most severe bleaching event ever with 17% to 20% coral
mortality.
zx Losses in the French West Indies ranged between 11% and 30%.
zx In the northern Dutch Antilles, there was 18% mortality in St. Eustatius, but
minimal mortality in Bonaire and Curacao in the south.
zx Trinidad and Tobago suffered considerable mortality, with 73% of all Colpophyllia
and Diploria colonies dying.
zx Although there was severe bleaching in the Greater Antilles, minimal mortality
occurred in Bahamas, Bermuda, Cayman Islands, Cuba, Jamaica and Turks and Caicos;
some sites in the Dominican Republic, however, suffered up to 38% mortality.
zx Bleaching mortality was minimal on the Mesoamerican Reef system, largely because
many storms cooled sea temperatures; however, Hurricanes Emily and Wilma
damaged some reefs, decreasing coral cover from 24% to 10%, especially around
Cozumel.
zx Coral mortality in Colombia and Venezuela was negligible.
zx Increased prevalence of disease following bleaching was reported from many islands
of the Lesser Antilles, particularly French West Indies; infection rates increased from
33% to 39% on Guadeloupe and 18% to 23% on St. Barthelemy; 49% of corals were
infected on Martinique.
zx In Trinidad and Tobago, there was clear evidence of an increase in the prevalence of
disease.
zx In the U.S. Virgin Islands, secondary disease infections killed bleached colonies of
Montastraea, Colpophyllia, Diploria and Porites.
2005 – lessons for management and future options
zx Unfortunately direct management action is unlikely to prevent coral bleaching and
mortality from climate change on most of the world’s reefs.
zx However, effective management can reduce the damage from direct human pressures
and encourage the natural adaptation mechanisms to build up reef resilience;
xii
Status of Caribbean Coral Reefs after Bleaching and Hurricanes in 2005
zx Such actions will promote more rapid recovery in the future, especially if bleaching
will become a regular event.
zx Unfortunately, current predictions are for more frequent and intense warming in the
Caribbean with the high probability of increased bleaching and coral mortality.
zx Severe coral bleaching is predicted to become a more regular event by 2030, and an
annual event by 2100, if the current rate of greenhouse emissions is not reversed.
in t r o d u c t i o n
The most extreme coral bleaching and mortality event to hit the Wider Caribbean (including
Atlantic) coral reefs occurred in 2005. This was during the warmest year ever recorded, eclipsing
the 9 warmest years that had occurred since 1995. The previous warmest year was 1998,
which resulted in massive coral bleaching throughout many parts of the world and effectively
destroyed 16% of the world’s coral reefs, especially in the Indian Ocean and Western Pacific.
Unlike the events of 1998, this climate-related bleaching event did not occur in an information
vacuum; this time there were many scientific tools available and alerts issued to those
working and managing coral reefs in the Caribbean to assess the damage and possibly prepare
management responses to reduce the damage. This book explains coral bleaching and follows
the sequence of the events leading up to it, and documents much of the damage that occurred
to the coral reefs and consequently to the people dependent on coral reefs for their livelihoods
in the Wider Caribbean.
This graph from the Hadley Climate Center in the UK shows that temperatures in the Northern
Hemisphere have been much higher in the last two decades and appear to be increasing from the
baseline of temperatures in 1960. The red line is a 10 year running average.
xiii
Executive Summary
It May 2005, analysis of satellite images by the National Oceanic and Atmospheric Administration
(NOAA) of USA showed that the waters of the Southern Caribbean were warming faster than
normal and people in the region were asked to look out for coral bleaching. The warming
was evident as a ‘HotSpot’ of warmer water which was likely to stress corals in the Northern
Caribbean (see p. ##).
As the surface waters continued to heat up, it became obvious that this was going to be a
particularly stressful year for the coral reefs of the Caribbean. NOAA issued a regular series of
information bulletins, warnings and alerts on the warming waters and developing hurricanes,
thereby stimulating coral reef managers and scientists to examine their coral reefs for signs
of bleaching. Throughout August, September and October it became clear in reports from the
Wider Caribbean that 2005 was probably the most severe coral bleaching and mortality event
ever recorded. The HotSpot warming reached its peak in October and then dissipated as winter
approached and solar heating shifted to the southern hemisphere. However, monitoring of
the corals continued into 2006 to assess either recovery from bleaching, or incidences of coral
disease or mortality. There were also preliminary assessments of the social and economic costs
of this HotSpot phenomenon.
The 2005 bleaching event has followed a long, slow decline in the status of Caribbean coral reefs
over thousands of years; especially during the last 50 years. Many Caribbean reefs have lost up
to 80% of their coral cover during this time. The causes included climate related factors prior
to 2005, but most of the coral losses were due to direct human impacts such as over-fishing,
excess sediment input, increases in nutrients from agriculture and domestic sewage, and
direct damage to reefs during development. These impacts are all symptomatic of increasing
human populations and their use of the reefs, such that many of these occur simultaneously.
The damage symptoms are often seen as particularly low fish populations, outbreaks of coral
diseases, or corals struggling to grow in poor quality, dirty waters or smothered by algae. Thus
many of the reefs of the Wider Caribbean were already stressed and in decline when the major
climate change events of 2005 struck.
The islands and mainland countries of the Caribbean are highly dependent on coral reef
resources, thus there is an urgent need for appropriate management responses as sea
temperatures are predicted to increase further in future. The World Resources Institute Reefs@
Risk analysis estimated that Caribbean coral reefs in 2000 provided between US$3,100 million
to $4,600 million each year from fisheries, dive tourism, and shoreline protection services;
however 64% of these same reefs were threatened by human activities, especially in the Eastern
Caribbean, most of the Southern Caribbean, Greater Antilles, Florida Keys, Yucatan, and the
nearshore parts of the Mesoamerican Barrier Reef System. All these areas suffered severe
bleaching damage in 2005. The R@R analysis indicated that coral loss could cost the region
US$140 million to $420 million annually.
This book compiles data and observations of coral bleaching and mortality from more than
70 coral reef workers and volunteer divers to summarize the current status of reefs in the
Wider Caribbean; but more importantly the book seeks to provide information to coral reef
managers and decision makers to aid in the search for solutions to arrest the coral reef decline
in a region that contains 10.3% of the world’s reefs. These compiled reports also illustrate the
value of early predictions of possible bleaching; ‘products’ developed by NOAA from archived
xiv
Status of Caribbean Coral Reefs after Bleaching and Hurricanes in 2005
and current satellite images, complemented by direct measures like temperature loggers and
buoys, were used to warn of the impending bleaching threat. The products were distributed
widely through e-mail alerts and various internet sites, alerting natural resource managers of
the potential for damage to their coral reefs. Hundreds of scientists and resource managers in
the Caribbean used these alerts and products in 2005 to allocate large amounts of their limited
financial and logistic resources to monitor what turned out to be a record-breaking bleaching
event. The information yielded from this monitoring will be vital to future management efforts
to protect coral reefs in light of today’s rapidly changing climate.
th E 2005 co r a l Bl E a c h i n g Ev E n t a n d hu r r i c a n E S
These following HotSpot images and the other ‘Degree Heating Week’ images on the front cover
and inside title page are typical of the information that was widely dispersed throughout the
Caribbean and elsewhere via the Internet through the coral reef information network ‘Coral-
List’. This generated considerable correspondence, and senior NOAA scientists have offered
their personal insight of what happened in their offices as the sequence of events developed.
These are detailed in Chapter 4.
This 1st figure illustrates a typical HotSpot image (explanation on p. ##) that was generated from
satellite data and distributed throughout the Wider Caribbean. The HotSpot on 16 July 2005 shows
waters 1ºC to 2ºC above the normal summer maximum as seen as ‘warm’ yellow and orange colors
over central America as well as a large but less warm region in the central Atlantic Ocean; as this was
being reported there was evidence of bleaching reported in Belize.
The first signs of bleaching were in Brazil in March during the southern summer. However
this did not correspond to a major HotSpot; it was more likely due to a local calm weather and
heating event. The first coral bleaching in the Caribbean was reported in early June on the Islas
del Rosario, northwest Colombia where waters had warmed to 30oC. These waters then cooled
and the corals recovered. By late June, surface waters exceeded 30oC around Puerto Rico, and
xv
Executive Summary
up to 50% of corals had already died. There was also bleaching on the Caribbean coast of
Panama, although this did not result in significant mortality.
In July, bleaching was reported in Belize, Mexico, Bahamas and in Bermuda and the US Virgin
Islands, which also coincided with reports of the death of large sponges in the US Virgin Islands
and off Cozumel in Mexico.
Although between 25% and 45% bleaching was reported in Belize and Mexico, the HotSpot
along the Mesoamerican Reef system dissipated with the regular passage of storms during 2005,
which prevented any significant bleaching related mortality. Despite the cooling benefits to the
region, Hurricanes Wilma and Emily caused considerable damage to coral reefs, especially
in Mexico around the island of Cozumel. Lower mortality in the Mesoamerican region may
be attributable to a reduced population of temperature sensitive corals, because previous
bleaching and disease events have removed the more sensitive species. It appears that the more
resistant species were only slightly affected. Coral cover has decreased markedly in the past 35
years, in some cases from near 80% to less than 20%.
This image from mid-August shows a dramatic expansion of two HotSpots with temperatures 2ºC
to 3ºC in excess of the summer maximum covering large parts of the Northern Caribbean including
Florida, the Flower Garden Banks in the Gulf of Mexico and just touching Cuba. The HotSpot in the
Atlantic has expanded alarmingly to cover all the islands of the Lesser Antilles; and there is a small
HotSpot over Colombia. Bleaching was being reported in all of these regions, as outlined in the
following chapters.
By early August, concern was growing that bleaching would damage the reefs of Florida and
the Gulf of Mexico. As the HotSpot expanded in the north, there were reports of extensive
bleaching in the Florida Keys, with water temperatures around 31°C and almost totally calm
and sunny conditions. In late August, extensive bleaching coincided with the warmest water
xvi
Status of Caribbean Coral Reefs after Bleaching and Hurricanes in 2005
ever recorded on Sombrero Key in Florida, but fortunately for these reefs, Hurricane Katrina
passed through the area as Category 1 storm resulting in considerable cooling of the waters
(see p. ##).
Similarly, bleaching increased around Puerto Rico involving all corals and coral-like animals
under hot calm conditions and the incidence of coral disease increased alarmingly. Severe
bleaching, up to 95%, was being reported from several islands in the Greater (Cayman Islands,
Jamaica, Cuba) and Lesser Antilles (Guadeloupe, Martinique, St. Barthelemy in the French
West Indies, St. Maarten, Saba, St. Eustatius in the northern Dutch Antilles, and Barbados).
Bleaching in the Cayman Islands was the worst ever recorded.
By early September, two major HotSpots with sea surface temperatures 2ºC to 3ºC more than normal
are covering Puerto Rico, the Virgin Islands and the other is still covering the Lesser Antilles. The
original HotSpot over the Gulf of Mexico and Florida has been effectively ‘blown away’ by Hurricanes,
especially Katrina that went on to devastate New Orleans on 29 August 2005 (see the Chapter on
Hurricanes p. ##). Reports of major coral bleaching were received corresponding to all the sites with
HotSpots.
The weather was particularly calm for two weeks in September, and was accompanied by
extensive bleaching on the south coast of Jamaica where about 80% of corals bleached. The
August bleaching on the north coast of Jamaica began to subside. Sea temperatures in the U.S.
Virgin Islands reached more than 30°C at 16 m depth. Bleaching affected most coral species.
More than 90% of corals bleached down to 30 m on the nearby British Virgin Islands. More
extensive bleaching continued on northern Puerto Rico. The bleaching footprint had expanded
to include Trinidad and Tobago and the Dominican Republic, reported bleaching in 85% and
68% of corals.
xvii
Executive Summary
The peak of HotSpot activity occurred in early October with a massive area of warm water covering
virtually all the central and eastern Caribbean. A series of Hurricanes had helped cool the waters
of the Northern Caribbean; but there were no hurricanes to pass through the Lesser Antilles where
the waters were warmest. In mid to late October the HotSpot ‘followed the sun’ southward and then
bathed the Netherlands Antilles and the northern coast of South America. By early November, the
HotSpot had virtually dissipated and conditions had returned to normal. However, this 4 month
period of unusually warm waters had wreaked havoc throughout the Wider Caribbean as is described
in the following chapters.
By October, dangerously elevated sea temperatures had been bathing the Lesser Antilles for
almost 6 months; most of this time the temperatures exceeded the normal coral bleaching
thresholds. This sustained thermal stress resulted in the most severe coral bleaching and
mortality ever recorded in the Lesser Antilles with 25% to 52% coral mortality in the French
West Indies, and the most severe bleaching event ever recorded around Barbados. Bleaching
affected all coral species at all depths. In the Netherlands Antilles there was 80% coral bleaching
around the islands to the north, near the British Virgin Islands, whereas around Bonaire and
Curacao in the south there was only minor bleaching and virtually no mortality. Further to the
east there was 66 to 80% bleaching of the coral cover on Tobago. On average, the accumulated
Caribbean thermal stress during the August-November period was greater than had been
experienced by these reefs during the previous 20 years combined.
A second bout of bleaching started when the HotSpot ‘followed the sun’ with Colombia seriously
affected in October and the peak bleaching in Venezuela in November and December 2005.
Bleaching was highly variable with sites reporting anything from zero to 100% bleaching, but
the mean was closer to 25%; fortunately mortality on reefs in tropical South America was far
less than on reefs to the north.
xviii
Status of Caribbean Coral Reefs after Bleaching and Hurricanes in 2005
Wh y cl i m a t E ch a n g E iS a t h r E a t t o co r a l rE E f S
Corals bleach when the coral animal host is stressed and expels the symbiotic zooxanthellae
(algae) that provide much of the energy for coral growth, and coral reef growth. Although
several different stresses cause bleaching, by far the most significant cause of coral bleaching
in the past 25 years has been sea surface temperatures that exceed the normal summer maxima
by 1 or 2oC for at least 4 weeks. This results in excessive production of toxic compounds in the
algae that are transferred to the host coral. The host coral reacts by expelling their symbiotic
algae, leaving the coral ghostly white and particularly susceptible to death from starvation
or disease. If conditions become more favorable, corals often recover, although they often
experience reduced growth and may skip reproduction for a season. In 2005, many bleached
corals did eventually die.
Coral bleaching was first noticed as a significant problem in the wider Caribbean region in 1983.
Concurrently there were increases in coral disease across the region, thus the assumption was
made that these were both associated with higher temperatures. The bleaching and outbreaks
of infectious diseases, such as white plague, have caused such major losses in the branching
staghorn and elkhorn corals (Acropora cervicornis and A. palmata), that they were added to
the List of Endangered and Threatened Wildlife under the Endangered Species Act of U.S.A. in
April 2007. The listing as Threatened Species dictates that US government agencies maximize
their efforts at conserving these species, which are the most characteristic of Caribbean reefs
and were once major contributors to reef construction.
The bleaching in 2005 ‘coincided’ with major outbreaks of coral diseases which saw extensive
shrinkage in the cover of live corals throughout the Caribbean. While many corals started to
recover when seawater temperatures dropped with the onset of winter, coral diseases broke out
and resulted in significant losses of coral cover, notably along the coast of Florida (Chapter 6),
in Belize (Chapter 5), the Virgin Islands (Chapter 7), and the Lesser Antilles (Chapter 8). The
accepted explanation is that bleached corals are stressed, lack reserve lipid supplies and are
effectively starving, making them more susceptible to disease.
Ocean acidification is a parallel climate change threat to coral reefs that results from increased
concentrations of CO2 dissolving in seawater, which reduces its pH. This process is called ‘ocean
acidification’, and by the end of this century, acidification may be proceeding at a rate that is
100 times faster and with a magnitude that is 3 times greater than anything experienced on
the planet in the last 21 million years. How this will affect marine ecosystems is unknown, but
impacts on marine calcifiers could be considerable. Using the pH levels expected by the end of
this century, laboratory studies show a significant reduction in the ability of reef-building corals
to grown their carbonate skeletons, making them both slower to grow and more vulnerable
to erosion. This would also affect the basal structure of coral reef itself. While the long term
consequences of ocean acidification on corals is not known, corals do not seem to be able to
easily adapt to such rapid changes. All predictions from climate change models point to this
becoming an equally severe threat to corals and coral reefs as bleaching.
Hurricanes and extreme weather events are also predicted to become more frequent and severe
as the pace of climate change quickens. There is increasing evidence that the proportion of
more destructive hurricanes has increased in recent decades, although the total incidence of
tropical storms has not increased. Stronger hurricanes will result in more severe wave damage
xix
Executive Summary
and flooding from the land, thereby adding an additional stress to already stressed reefs. Low
to moderate strength hurricanes can be beneficial during summer, however, by cooling surface
waters and reducing the likelihood of coral bleaching.
There is insufficient evidence or indications that the other potential climate change stresses
will result in significant damage to coral reefs. There is a potential for negative impacts from
possible shifting of ocean currents or associated rises in UV concentrations; however these are
not evident at the moment. Sea level rise will not directly threaten corals, but may render coral
reef islands uninhabitable, thereby threatening coral island cultures and nations.
im p l i c a t i o n S o f 2005 f o r co r a l ma n a g E r S
Coral reef managers were unprepared for the climate-related destructive events of 1998. Many
coral reef managers in the Indian Ocean and Western Pacific reported that massive coral
bleaching in mid to late 1998 was devastating their coral reefs, and they asked ‘what have I done
wrong to cause the corals to die’. They were perplexed that corals were dying on the same reefs
that they were actively managing to remove pollution, sedimentation and over-fishing stresses.
The cause of the problems to their reefs was related to climate change via a particularly severe
El Niño and La Niña climate switch that raised sea surface temperatures (SSTs) above levels
that had ever been recorded on those coral reefs. We now know that no management actions
could have prevented the extent of coral death; the only advice the coral reef research and
management community could offer was that ‘better managed reefs will recover more rapidly
than those under human stresses’.
The events of 1998 stimulated the international coral reef community to develop advice for
coral reef managers faced with similar circumstances in the future. A Reef Manager’s Guide
to Coral Bleaching was developed in 2006 to provide that advice for coral reef managers faced
with stresses beyond their immediate control. The report is summarized by the authors in
Chapter 10 and provides reef managers with the explanations why reefs are damaged by such
climate related events and explains why some reefs resist coral bleaching and others are more
resilient i.e. they recover faster after severe losses.
The report guides reef managers into steps they can take at national and global levels to raise
awareness of the potential devastation that increasing global climate change, though the release
of greenhouse gases, can have on coral reefs. However, the emphasis is on providing managers
with practical advice on how to increase protection of those reefs that are either naturally
resistant or tolerant to bleaching, assist in promoting adaptation mechanisms that enhance reef
resilience, while simultaneously reducing local pressures on the reefs and nearby ecosystems
to enhance chances for natural recovery. Importantly, the Guide advises reef managers on how
to engage with local people and assist in maintaining socioeconomic well-being and bringing
them on board to assist in the sustainable use of their coral reefs.
an d t h E fu t u r E
Sadly for coral reefs, all predictions from the Intergovernmental Panel on Climate Change
(IPCC) reports in 2007 indicate that the extreme warming of 2005 will not be an isolated event
(Chapter 11). It will probably happen again in the future and, when it does, the impacts will
be even more severe. The IPCC concluded that human-induced climate change will warm the
xx
Status of Caribbean Coral Reefs after Bleaching and Hurricanes in 2005
world by 1.8 to 4.0ºC by the year 2100. This warming will affect most of the wider Caribbean
Sea making years like 2005 more common and more devastating for coral reefs.
In addition, increasing acidity in the seawater with the solution of more CO2 will result in
slower growth of corals that are trying to recover from bleaching and other disturbances.
One other potential consequence of the human-induced warming is an increase in the frequency
of more damaging Category 4 and 5 hurricanes in the Caribbean. These storms develop as
waters warm over the tropical North Atlantic and Caribbean waters. It is predicted that warmer
surface waters with increased amounts of thermal energy will fuel increases in tropical storm
strength. The latest predictions are for an increase in the more intense Category 4 and 5
hurricanes that will probably cause significant damage to the coral reefs and the communities
that depend upon them (Chapter 3).
This figure shows the proportion of intense hurricanes has been increasing since 1970 while the
total number of hurricanes has not changed much. These graphs plot all global hurricanes combined
into 5 year periods from 1970 to 2004, with projected trends added to 2019. Category 1 storms are
relatively weak whereas Category 5 storms are particularly devastating (adapted from Webster 2005).
Dashed lines show significant linear trends.
This is a pivotal moment for the coral reefs. The world is already committed to some further
warming due to past greenhouse gas emissions and the expected emissions from existing world
energy infrastructure (Chapter 2). Thanks to more than a century of ‘committed warming’;
events like 2005 are expected to occur more frequently by the 2030s. The only possible way to
sustain some live coral on the reefs around the world will be to carefully manage the direct
pressures like pollution, fishing and damaging coastal developments, and hope that some
coral species are able to adapt to the warmer environment. However, a dramatic reduction in
greenhouse gas emissions in the next 20 years will be critical to control further warming and
dangerously high CO2 levels that will probably reduce the robustness and competitive fitness of
corals and limit the habitats for many other organisms living on Caribbean coral reefs.
Category 1
Category 2 & 3
Category 4 & 5
5 – year period
50
20
10
30
40
0
70-74 75-79 80-84 85-89 90-94 95-99 00-04 05-09 10-14 14-19
% Hurricanes per category
