Final answer:
A large percentage of coral reefs are at risk of disappearing by 2030 due to climate change, oceanic acidification, pollution, and overfishing. The exact percentage is not specified, but these threats indicate a potentially severe decline.
Step-by-step explanation:
A significant percentage of coral reefs could disappear by the year 2030 due to various environmental stresses. Climate change, characterized by the increase in sea temperature, poses a substantial threat to coral reefs, leading to conditions where recovery may not be possible.
Additionally, other human activities such as allowing agricultural runoff and pollution to enter the oceans contribute to the decline of these ecosystems. Oceanic acidification, also primarily caused by increased levels of carbon dioxide in the atmosphere dissolving into the oceans, is progressively weakening coral structures.
This complex situation is exacerbated by overfishing, which disrupts the ecological balance and allows predatory species that consume coral to flourish. The exact percentage is not provided in the reference material, but the severity of these threats suggests extensive damage if actions are not taken to mitigate these issues.