Final answer:
Global warming leads to rising sea levels from melting glaciers and water expansion, which can inundate coastlines and reduce island sizes. It also disrupts the freshwater cycle and increases ocean acidity by absorbing more carbon dioxide, threatening marine ecosystems.
Step-by-step explanation:
Global warming has far-reaching effects on the oceans, which are an integral part of the Earth's climate system. The phenomenon of global warming leads to rising sea levels due to meltwater from glaciers and the thermal expansion of seawater as it warms. This poses a threat to coastal areas as shorelines become inundated, leading to the reduction in size of islands, with some disappearing entirely. Furthermore, global warming affects the freshwater cycle, as the consistent melting and freezing of polar regions will be disrupted, impacting the availability of fresh water.
The oceans also act as a carbon sink, absorbing significant amounts of carbon dioxide from the atmosphere. As they absorb more CO2, the waters become more acidic, leading to changes in pH levels that can disrupt marine food webs, damaging coral reefs and affecting the survival of various marine species such as salmon. Thus, the increase in ocean acidity is a direct result of the ocean's role in moderating climate change by absorbing excess heat-trapping gases.