The average sea level has risen about 24.9 centimeters since 1880. The two main factors of global sea level rise are the thermal expansion caused by the warming of the ocean and the melting of glaciers and ice sheets. To be more specific, the warming of the ocean is due to the greenhouse gas because the oceans absorb more than 90 percent of trapped greenhouse gases' heat. For the same reason, glaciers and ice sheets melt because of the warming of the ocean. 

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The first graphic figure above shows the change in sea level in millimeters from 1880 to 2022. The lines in light blue and black are both adapted by NOAA Climate, although the data in the black line is based on the University of Hawaii Sea Level Center's analysis. It only contains the 1993-2008 average values, yet it correlates with the line in light blue with a minor discrepancy. Combining them, it is obvious that the global sea level is rising regardless of the measure type. The second figure is also from NOAA Climate, and it shows how the thermal expansion of the ocean and the meltwater contributed to the rise in global sea level. 

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As a result, sea level rise has harmful impacts on people living in coastal areas. Those areas become more susceptible to flooding when storm surges, and residents may experience property and economic losses. Not only that, residents in coastal areas have a chance to get contaminated drinking water due to the intrusion of saltwater. Some countries experiencing these are Maldives, Tuvalu, Kiribati, and Bangladesh. 

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As shown above, Nature Communications analyzed how rising sea levels would threaten people. According to the research of Kulp and Strauss, an estimated 200 million people worldwide will reside below sea level and another 160 million will face more frequent annual flooding due to rising ocean levels by 2100.