The rising sea level refers to the increase in the average level of the water over a period of time. The reason it is rising is because of global warming that is caused by greenhouse gas emission. When the earths temperature is rising, ice from around the world like glaciers and ice caps melt and add more water to the ocean. when this happens it causes coastal villages and other things near there to erode and soon enough be under water. There are efforts to reduce the emissions and stop the green house gases and earth's temp to rise.