The global sea levels have risen more rapidly since the early 20th century than in the last 3,000 years, with an increase of over 20 cm since records began in 1880. The World Meteorological Organization reported that average global sea levels reached a historic high in 2023. This rise is not uniform worldwide, influenced by ocean dynamics and Earth's gravitational field.
The speed of sea level rise is primarily driven by global warming. If temperatures can be kept below 1.5 degrees Celsius, as outlined in the Paris Agreement, global sea levels could rise an additional 38 cm by 2100. However, current climatic trends, with temperatures around 2.7 degrees Celsius, could lead to a rise of 56 cm.
Even a few centimeters can have drastic effects; scientists estimate that each 2.5 cm increase equates to the loss of 2.5 meters of beach, leading to higher tides and storm surges. For every centimeter of sea level rise, an additional 6 million people are exposed to coastal flooding. In extreme scenarios, human activity could cause sea levels to rise by up to two meters by the end of the century.
Global warming is exacerbated by emissions of carbon dioxide, methane, and other gases from fossil fuel combustion, which also warms the oceans. The seas have absorbed nearly 90% of atmospheric warming over the past 50 years, with ocean warming rates doubling in the last two decades, particularly in the southwestern Pacific.
Melting ice sheets and glaciers contribute to an annual loss of about 150 billion tons of ice mass in Antarctica and 270 billion tons in Greenland. Recent studies suggest that temperatures exceeding 1.5 degrees Celsius could trigger the irreversible collapse of all ice sheets in Greenland and West Antarctica, leading to significant sea level rise.
Low-lying islands such as Fiji, the Maldives, and Tuvalu face existential threats from rising seas, along with 40% of the global population living near coastlines and approximately 900 million people in low-lying areas.
Coastal cities and communities worldwide are already battling coastal erosion, saltwater intrusion, and increasingly destructive storms and floods. Future studies predict severe impacts in tropical regions of Asia, particularly in Bangladesh, India, and China, as well as in river deltas and port cities. Megacities like Cairo, Lagos, Los Angeles, Mumbai, Buenos Aires, and London will face significant challenges.
Experts suggest that the key to preventing dramatic sea level rise is to rapidly reduce emissions. However, some level of sea level rise is inevitable due to the lag between global warming effects on ocean temperatures and ice melt.
Many countries are adopting various adaptation measures, including the construction of levees and storm surge barriers, improving drainage systems, and building flood-resistant structures. For small island states, responses include relocating entire villages to higher ground, building floating cities, and reclaiming land from the sea.