These changes have occurred rapidly and ecosystems are facing a major adaptation challenge (Ove). Coral bleaching has always occurred due to environmental stresses such as temperature changes, salinity changes, pollution, overfishing, and so on (Chapter 1). This means that climate change is not the only factor contributing to coral bleaching, but is gaining high recognition as the main contributing factor on a global scale (ch. 1). The main difference between past and current bleaching events is localized events versus globalized events. The increase in the greenhouse effect has created an increase in the frequency and size of coral bleaching events caused by thermal increase (chap. 1). These are known as mass bleaching events, this is where entire coral reefs are affected by coral bleaching and are no longer just localized (ch. 1). Mass bleaching events occur because the reef is exposed to higher temperatures for a longer period of time, rather than for a short period of time, during which the corals can then recover (Ove). The length of time a reef is exposed to a particular anomaly can be analyzed with “degree warming weeks,” also known as ACS (Ove, 395). If coral reefs are exposed with a value less than 4 ACS then the coral is likely to recover quickly, if the ACS value is above 12 the coral reefs will have devastating effects (Ove, 395). The ACS model calculates all hot spots over a 12-week period, while the hot spot product measurement alone is a measure of instantaneous heat (Chapter 4). The ACS shows where widespread coral bleaching occurs along with severity (Ove). When a value of 2DHW is given, this means that the hotspot is 1˚C warmer for 2 weeks, or 2˚C for 1 week (ch. 2). Refer to Figure….to review the global ACS