As you just observed, the ocean's surface is rising. One of the major contributors to sea level rise is thermal expansion. When water warms, it expands and takes up more space. In addition, melting glaciers and polar ice sheets add more water to the oceans. Rising sea level erodes beaches and coastal wetlands and can flood low-lying areas. Coastal Flooding is a serious concern of 600 million people living in low-lying areas on Earth. Ecosystems can also be disrupted as coastal areas flood.