Graph of the Day: Regions Most Vulnerable to Flooding Caused by Sea Level Rise
Global mean sea level has already risen by about 25cm since the 1800s, and the pace is accelerating. Levels rose by approximately 1.8mm per year over the last five decades, doubled to 3.1mm per year in the 1990s, and were 2.5mm per year in the period 2003–2007. Sea level rise is caused by melting glaciers and ice caps, loss of ice from major ice sheets in Greenland and Antarctica, thermal expansion of the ocean, and changes in terrestrial storage. Melting ice has been the dominant source of sea level rise for about the last decade. How rapidly the major ice sheets will respond to further increases in temperature is dependent on dynamic processes and feedback loops and remains uncertain; this will be the major determining factor in future sea level rise. In Greenland, ice loss already increased by a factor of seven in the decade between the mid-1990s and the mid-2000s. In parts of Antarctica, ice loss nearly doubled in the same period. Although our understanding of these processes is growing, obtaining a precise estimate for sea level at the end of the century remains beyond our abilities. The projections for sea level rise by 2100 vary between a minimum of 0.2 metres and a maximum of about 2 metres. What is known is that while sea level rise will impact all coastal areas, it will do so to differing extents. Sea level is an existential threat for some small island developing states (SIDS), which will disappear entirely with even modest increases. Other, more widespread, impacts include submergence and flooding of coastal land, saltwater intrusion, increased erosion, and habitat destruction. The highest risk areas are coastal zones with dense populations, low elevations, high rates of land subsidence, and limited adaptive capacity. Figure 1.2 shows the locations of these vulnerable regions, which include the entire coast of Africa and South and Southeast Asia, as well as Pacific, Indian Ocean, and Caribbean islands. Approximately 145 million people live within 1 meter of mean high water, more than 70% of whom are in Asia, and 268 and 397 million live within 5 and 10 meters, respectively. National security could be threatened in certain cases if low-lying areas that are key to the functioning of vulnerable states are decimated by rising seas. People living in at-risk coastal areas have essentially two choices about how to respond to increasing sea level: fight or flee. Fighting involves improving or building coastal defenses – seawalls, dikes and other built infrastructure. Fleeing involves relocating people from low-lying areas to higher ground. The international community must recognize that considerable damages and costs can be avoided through adaptation measures taken now. The people who stand to be most affected by climate change are among the least responsible for greenhouse gas emissions: innovative strategies, financial instruments and funding mechanisms must be mobilized to address their urgent needs.
