Climate Change and the World's Coral Reefs

What does this report tell us?

This scientific study concludes that if climate change is not stopped, coral bleaching is set to steadily increase in frequency and intensity all over the world until it occurs annually by 2030 - 2070.

This would devastate coral reefs globally to such an extent that they could be eliminated from most areas of the world by 2100. Current estimates suggest that reefs could take hundreds of years to recover. The loss of these fragile ecosystems would cost billions of dollars in lost revenue from tourism and fishing industries, as well as damage to coastal regions that are currently protected by the coral reefs that line most tropical coastlines.

This study, conducted by Professor Ove Hoegh-Guldberg, one of the world's leading experts in coral bleaching, uses leading climate projection models from Germany's Max Planck Institute and Australia's CSIRO - some of the same models used by the United Nations as the basis for the development of the UN's Climate Change Convention. By putting advanced climate and coral science together, he was able to calculate time lines showing the fate of coral reefs if we continue to increase greenhouse gases in the atmosphere. The pattern of coral bleaching is consistent between all oceans. Coral bleaching will increase in frequency and intensity and is projected to devastate reef systems by early next century.

What is coral bleaching?

Coral bleaching is a condition that can seriously damage or kill entire reef systems. Corals contain microscopic plants called zooxanthellae that colour their tissues and provide them with food by photosynthesis - the same process that plants manufacture food from light. Without these tiny plants corals cannot survive or lay down the huge amounts of limestone in their skeletons. When corals become stressed, the zooxanthellae are the first to go. Stressed corals expel the zooxanthellae and turn white or "bleach". If zooxanthellae do not return to the coral's tissue, the coral will die.

Because of the increasing intensity and geographic scale of recent bleaching events, mass bleaching is considered by most reef scientists to be a serious challenge to the health of the world's coral reefs. The worst coral bleaching ever was recorded in 1998. Every reef system in the world's tropical oceans was affected. In some places, such as the Indian Ocean, entire reef systems died.

What causes coral bleaching?

This report concludes that increases in ocean temperatures are causing the rise in the intensity, frequency and extent of coral bleaching.

The six major episodes of coral bleaching over the past 20 years have been caused by periods of increased water temperature. Corals are highly sensitive and can only live in water between 18 to 30 degrees Celsius. Most bleaching events are explained by a 1 degree Celsius increase in temperature above the summer maximum water temperature.

Tropical sea temperatures have increased by 1 degree Celsius over the past 100 years and are currently increasing at the rate of 1-2 degrees per century.

Mass death of corals frequently and increasingly follows bleaching events. In addition to killing corals, increased temperature has recently been found to affect coral populations by reducing their reproductive capacity and their ability to grow.

Increasing levels of greenhouse pollution from the burning of coal, oil and gas are pushing up average global temperatures. This is recognised by the majority of scientists, the United Nations and governments around the world.

How long will it be until the reefs are seriously damaged?

The report points to the urgency of addressing the climate change problem. Based on the current and projected increases in sea temperature, the next generation of children will not grow up to see healthy coral reefs. Estimates of increased sea temperatures show that bleaching events will steadily increase in frequency and intensity. Within the next 30 years they are projected to occur every year in most tropical oceans.

The worst mass bleaching event occurred in 1998 with coral reefs being affected in 30 large-scale incidents worldwide, including Australia, China, Japan, Panama, Thailand, Malaysia, the Philippines, India, Indonesia, Kenya, the Red Sea, Puerto Rico, Jamaica, the Bahamas and Okinawa. Events as severe as the 1998 event are projected to become a commonplace annual event by around the year 2020.

Australia's Great Barrier Reef is expected to face bleaching events every year by around 2030. At current rates of warming, southern and central sites of the Great Barrier Reef could be severely affected by sea temperature rise within the next twenty years. Northern sites are warming more slowly and will lag behind changes in the southern end of the Great Barrier Reef by up to 20 years.

Globally, some regions will experience the effects of climate change on their reefs sooner than other areas. Caribbean and Southeast Asian coral reefs are projected to bleach every year by 2020. Central Pacific reefs are projected to experience bleaching every year by 2040.

Can't coral adapt to warmer temperatures?

Corals do not appear to show any sign that they are able to adapt fast enough to keep pace with changes in ocean temperature. Arguments that corals will adjust to predicted patterns of temperature change are unsubstantiated and most evidence shows that bleaching events are signs that the genetic ability of corals to acclimate is currently being exceeded. Corals may adapt in evolutionary time, but such changes are expected to take hundreds of years, suggesting that the quality of the world's reefs will decline at rates that are faster than expected.

This has enormous implications for the health and wealth of tropical and subtropical societies.

In addition to current and predicted rates of increase in sea surface temperature, coral reefs are also directly threatened by changes in atmospheric carbon dioxide and by rising sea levels. Current estimates show that atmospheric carbon dioxide levels expected around the middle of next century will inhibit the ability of corals to lay down their limestone skeletons by a massive 30%. Because corals have to sustain high rates of skeletal construction to enable reefs to maintain their current extent and distribution, this additional problem (together with coral bleaching) is expected to hasten the loss of coral reefs worldwide.

These changes, combined with the increasing stress on reefs from human-related activity, suggest that coral reefs may be dysfunctional within the near future. The current understanding of coral bleaching suggests that corals may be the single largest casualty of "business-as-usual" greenhouse policies. What will it mean if coral reefs are devastated?

The economic impact of these changes could run into trillions of dollars and would affect hundreds of millions of people worldwide.

Globally, many people depend in part or wholly on coral reefs for the livelihood and around half a billion people live within 100 kilometres of coral reef ecosystems. Tourism alone generates billions of dollars for countries associated with coral reefs - $1.5 billion is generated annually by Australia's Great Barrier Reef, $2.5 billion by Floridean reefs and many billions by Caribbean reefs.

Tourism is the fastest growing economic sector associated with coral reefs and is set to double in the very near future. One hundred million tourists visit the Caribbean each year and according to the US State Department, SCUBA diving in the Caribbean alone is projected to generate $1.2 billion by the year 2005.

The fisheries associated with coral reefs also generate significant wealth for countries with coral reef coastlines. Fisheries in coral reef areas also have importance beyond the mere generation of monetary wealth and are an essential source of protein for many millions of the world's poorer societies. For example, 25% of the fish catch in developing countries is provided from coral reef associated fisheries.

While coral reefs will not become extinct in the long-term, their health will be severely compromised for at least 500 years unless warming is mitigated. The implications of this projection are enormous and must be avoided at all costs.

Isn't coral bleaching a natural phenomenon?

Mass coral bleaching has attracted widespread attention over the last 20 years due to an increase in the frequency and intensity of bleaching events that have affected reef-building corals all over the world. Six major periods of mass-bleaching across thousands of square kilometres have been reported in scientific literature since 1979, and there is compelling evidence that coral bleaching has not occurred with anywhere near this frequency prior to 1979.

Mass coral bleaching has not been reported by either reef users or scientists before 1979. It is telling that there is no term for coral bleaching in the native language of any of the societies that have lived with coral reefs for thousands of years. In short, mass coral bleaching is clearly a new phenomenon in all parts of the world.

This report presents compelling evidence that raising ocean temperature is the cause of observed large-scale bleaching and death over the last 20 years.

Who is Professor Hoegh-Guldberg?

Professor Hoegh-Guldberg has spent the past 15 years investigating why coral reefs throughout the world have suffered from increasingly severe bleaching. In 1994 he published a report on research on global warming and coral reef ecosystems. This document was of sufficient significance that it was read by U.S. Vice-President Al Gore and provided crucial evidence in the effort to set up the U.S. Coral Reef Initiative. Professor Hoegh-Guldberg has led the way in understanding this major change in a key tropical ecosystem, and has increased our capacity to potentially manage what now appears to be a serious threat to the health of coral reefs.

Professor Hoegh-Guldberg was the winner of the prestigious 1999 Eureka Prize for Scientific Research for his work on why coral bleaching occurs.

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