Under the "worst case" scenario, global mean sea-level is expected to rise almost one metre by the year 2100, affecting more than 140 million people in China and Bangladesh alone, with large local differences due to tides, wind and atmospheric pressure patterns, changes in ocean circulation, vertical movements of continents etc.
Evidence for fluctuations in sea level during the current inter-glacial suggest that factors other than thermal expansion and ice melt (i.e. greenhouse effect) may be a factor. Large fluctuations in lake levels and groundwater on land masses, caused by changes in monsoonal flows, could for example be large enough to induce changes of up to 4-8m. There is evidence that such large land water changes have occurred in north Africa and India.
For the past five years the Intergovernmental Panel on Climactic Change, created as a result of a 1992 U.N. treaty, has been assessing data and studies to develop a long range climactic forecast. In so doing the scientists say they are 90-to 95% convinced that the chief cause of the developing changes is the emission of greenhouse gases. While agreeing that human activity (notably burning wood and fossil fuels) is at least partially responsible, the panel said it was not yet possible to determine how much of that is man-made and how much due to natural causes.
Among some of the experts' predictions: The average sea level world-wide will rise more than 45 cm by 2100, rendering uninhabitable many heavily populated river delta regions, including entire cities, mostly in Asia. The result will be a new class of disaster victim: environmental refugees. On the eastern seaboard of the USA, beaches that are already disappearing at the rate of 60 to 90 cm a year, will be gone in 25 years.
There is evidence to indicate that sea levels may rise over the next 50 years, sufficiently to radically change the boundaries between coastal nations, to cause some island countries (such as the Maldives) to disappear, and to change the shapes and strategic importance of international waterways. Global estimates based on the period 1881-1980 indicate a rate of sea level increase of approximately 1mm per year. It is also estimated that by 2030 sea level will be rising at about 4mm or 5mm a year. 50 million people could be made homeless by flooding caused by rising sea levels in Bangladesh and Egypt.
Climate change, resulting in sea-level rise and flooding or erosion of low-lying coastal areas and lagoons, will have serious adverse impacts on ecosystems, water resources, coastal zones and human settlements, particularly in the countries of Western and Central Africa, the Nile Delta and the Indian Ocean island states.
In 2017 it was reported that five tiny Pacific islands in the Solomon Island archipelago had disappeared due to rising seas and erosion, a discovery thought to be the first scientific confirmation of the impact of climate change on coastlines in the Pacific, according to Australian researchers. The missing islands, ranging in size from 1 to 5 hectares (2.5-12.4 acres) were not inhabited by humans. But six other islands in the archipelago had large swaths of land washed into the sea and on two of those, entire villages were destroyed and people forced to relocate.