There also would be changes in current and wave action, which can damage reefs. The effects are hard to predict, but they could be locally important. The CaCO 3 of coral reefs is a major global carbon reservoir. Reefs often are thought of as carbon sinks, because CO 2 from the atmosphere is converted into calcium carbonate rock. Actually, coral reefs are a minor source of atmospheric carbon.
Anthropogenic damage is still the most serious problem facing reefs.
Serious and immediate human impacts include mining for cement, dynamiting to kill fish, and anchoring of pleasure boats. Overall, coral reefs are not as seriously threatened by climate change as by human impacts. Annual rings appear as alternating dark and light bands when corals are sectioned and x-rayed, due to a seasonal cycle of high verses low density of coral secretion. The causes of this cycle are uncertain but probably nutritional. Some coral colonies on the Great Barrier Reef are 600 to 1,000 years old.