The sea level (SL) at Sundarbans started rising at the onset of the Holocene era, then gradually slowed down at 7,000 years before the present (BP), and then it nearly stabilized at 2,000~3,000yr BP. There was a steady increase in SLR by 1.7 mm yr-1 throughout the 19th century, but it escalated to 3mm yr-1 during the final decade of the 20th century (4th IPCC). From 1990 to 2019, thermal expansion of seawater and melting of land ice contributed to about half of the SLR. Average rate of SLR was estimated to vary from 1.4 to 2 mm yr-1 during the last century. Our estimation, however, is about 4 mm yr-1 up to the year 2090 after considering the future scenarios. Using tidal gauge data, we have found higher rate of SLR in the study area compared to worldwide trends. On analyzing temporal Landsat images, it was found that the mangroves covered about 1599.9 sq. km in the year 1990 and 1582.4 sq. km in the year 2019. Thus a significant amount (8.5 sq. km) of mangrove area has been lost during the study period. The results point out that SLR, combined with anthropogenic development, has caused the forests' depletion.