The very first thing to know is that coral can live in a huge variety of circumstances, coral as a species is under no risk at all. The best comparison to coral as a species is to that of mold. There are mold spores in almost all places on the Earth. Bread gets moldy because the spores find a place to start growing and that is what they do. Coral in the ocean is much the same. The ocean is filled with seeds of coral that basically start growing anywhere they find the right conditions.
So while coral is not at risk, the proposed risk is to the highly specialized coral reefs. These are known as the shallow-water coral reefs. These tropical shallow water reefs can live in a variety of temperatures, but not at a temperature lower than 18 °C. The most important aspect of these reefs is the depth of the water. They cannot live in water that is deeper than 50m (165 ft)i.
Nothing limits this shallow water coral more than those two combinations. They must have shallow, warm water. That is why this type of coral is found in such a narrow ecological niche. They are generally found in the tropics (+/- 30 degrees of the equator, but can be outside of that if conditions are correct) and only in places where the water is warm. There are many places that don’t have coral in the tropics because the water is too cold for this type of coral.
These tropical coral reefs survive as part of a parasitic or symbiotic relationship (depending on your definition) with algae. They capture algae and the algae uses photosynthesis to feed the corali. So coral survives by using the energy from the algae that is trapped within. This is why these corals need shallow water to survive. Deep water prevents photosynthesis in the algae and that is what limits the range of coral reefs. Anything else that interferes with the coral feeding off of the algae causes the coral to turn white. It is this coral turning white that is called coral bleaching.
Coral bleaching is the first step to telling if there is something causing problems for the coral. Most of the time a coral that bleaches will not die. If it stays bleached for a long enough period (usually weeks) then the coral can start dying. There are many things that can cause bleaching. The reason that coral usually recovers from bleaching is the conditions that interrupt the food cycle between the algae and the coral stop and the coral starts getting energy from the algae again. Once the coral starts eating again it recovers much like any other hungry animal.
The main cause of coral bleaching is quickly changing temperature. If the temperature changes quickly, the coral will bleach. One of the greatest pieces of misinformation is that coral can only withstand a temperature change of 1-2 °C. The temperatures of all oceans vary much more than that during the course of a year. It is only when the temperature changes quickly that coral runs into trouble. As you will see in the later articles, it is abnormal temperature events that cause coral bleaching. The main culprits of these events are those very pesky, but natural ocean oscillations.
The other proposed impact of CO2 on coral is that of ocean acidification. What this means is that increasing CO2 levels in the atmosphere are causing the pH level of the ocean to become more acidic (pH drops). Of every impact blamed on CO2 emissions, this is in reality the most scientifically viable. Increasing CO2 levels do in fact have a slight impact on the ocean pH, but as part 3 will show, the ocean pH levels naturally change in response to the normal variations in the Earth’s climate. This is especially true when the climate is changing quickly.
Source information. The single article has endnotes and when all the articles are out I will add all of them in that final article.