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Swept Away by Global Warming
Global warming is transforming our environment. The temperature, acidity and water level of the ocean is rising. These changes are increasing in speed and magnitude and their effects will last for centuries. Corals are among those organisms hit hardest by global warming. The rate our climate changes will determine whether coral can survive or not.
Over 30% of coral reefs are seriously damaged, and this is likely to rise to 60% by 2030. One major cause of this damage is global warming. Global warming and other sources of disturbance, like pollution and overfishing, work together to harm the coral reef ecosystem.
Some types of disturbance are relatively easy to control because they impact ecosystems within a small area. But global warming acts on a global scale with no one source of disturbance.
In next 50 years, temperature and carbon dioxide (CO2) levels are likely to be higher than they have been in the last 500 000 years. This will change the climate dramatically, and these changes will probably happen very quickly.
Global warming damage coral reef ecosystems in 3 main ways, by:
Warming the average temperature of the ocean by just 2-3oC is enough to kill many corals. High water temperatures harm coral in 3 ways, by:
Reef-building coral shelter zooxanthellae algae in exchange for food. Warm water temperatures stop zooxanthellae from making food. Algae leave the coral and it turns white without algae to color it. This process is called coral bleaching. Coral can survive for short periods without zooxanthellae, but will die unless it gets more (see "Coral bleaching" for more information).
Rising water temperatures also increase the incidence of coral disease. Unfortunately, disease spreads more easily on densely packed reefs, and can hit a healthy reef harder than a reef that has already lost coral cover.
The ocean helps drive weather patterns, and warming seawaters will increase the frequency and strength of tropical storms. The health of coral reefs will erode if storms happen too frequently because they won’t have time to repair damage from one storm before the next hits. Coral reefs protect coastal property from erosion (see "How reefs protect the land" for more information). Tropical storms will have a much greater impact on coastlines and coastal property if coral reefs are lost.
The ocean absorbs carbon dioxide (CO2) from the atmosphere, and some of this CO2 turns into carbonic acid. The ocean has absorbed so much extra CO2 from industrial sources that it is becoming more acidic.
An acidifying ocean weakens reefs by dissolving the skeleton of coral polyps (see "What is a coral?" for more information). By 2050, the sea may be too acidic for coral polyps to produce a skeleton at all.
Average sea levels are rising, and this rate is probably increasing. The average sea level is projected to rise from between ¼ to 3 feet (8cm–1m) by 2100. Rising sea levels will increase wave action and erosion. This increased erosion will need to be countered by growth.
Coral reefs appeared about 500 000 years ago, and have been adapting to changing climates ever since. But we are rapidly approaching temperatures and CO2 levels higher than corals have ever experienced.
Several factors will determine whether coral adapt to the present climate change caused by global warming, including:
Rate of change
Rate of growth
Relationship with zooxanthellae algae
The rate that global warming changes the climate will be a big factor in determining whether coral reefs can survive. Coral reefs can adapt to many types of disturbance (and even benefit from a certain amount). But when the disturbance rate becomes too high the reef has no time to recover and its health erodes.
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