This video actually provides a good answer on why we need to speak about Global Change instead of Global Warming.
Ocean acidification is the ongoing decrease in the pH of the Earth’s oceans, caused by the uptake of carbon dioxide from the atmosphere. An estimated 30–40% of the carbon dioxide released by humans into the atmosphere dissolves into oceans, rivers and lakes.
Increasing acidity is thought to have a range of possibly harmful consequences, such as depressing metabolic rates and immune responses in some organisms, and causing coral bleaching.
The acidification of the oceans is not a new phenomenon but it is mainly the rate at which it is occurring that worries scientists.
Source: California Academy of Science