Besides the air getting warmer due to global warming, the ocean waters are getting warmer too. One reason for the oceans getting warmer is due to the air getting warmer. The warmth of the air always affects the temperature of the ocean water. This increase in temperature causes melting of ice caps along with the air. This can make the sea levels rise.
At first this may not seem like a big deal, but rising sea levels are a problem. When the sea levels rise, this can cause flooding. This flooding can occur in major cities that are along the coasts. These cities are not equipped to deal with flooding and this can cause a lot of damage to the cities as well as injury or fatalities to the people who live in the city.