The answer is; Rising temperatures may melt the polar caps and increase the ocean water levels.
Global warming is due to the increase in the levels of greenhouse gases, such as carbon dioxide, in the atmosphere. These gases trap reflected radiation from the earth that heat up the atmosphere. The warming atmosphere also warms the polar regions. This consequently results in the melting of glaciers and these melted waters flow into oceans increasing their water levels. Increased ocean levels eat up into the beach shores and also swallow up small islands.