Rising Sea Levels

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Rising Sea Levels

Climate change has had a significant impact on global sea levels; as the global temperature increases, the height of sea levels does as well. Throughout the earth’s history, the sea level has been hundreds of feet higher and lower than today’s present height, due to the natural climate cycle of ice ages and interglacial periods (1). These climate cycles produce warm and cool periods on earth, and during these warmer periods, the sea level rises. However, human-induced climate change and warming has led to an accelerated rise in sea levels. 


Rising sea levels will infiltrate coastal cities and urban populations will be force to migration either temporarily or permanently. Image Source: http://www.migrationpolicy.org/programs/migrants-migration-and-development 

Over the past century, the burning of fossil fuels and other human and natural activities has released large amounts of heat trapping gases into the atmosphere (2). These gas emissions have caused the earth’s surface temperature to rise, and the oceans absorb about 80% of this additional heat (2). This is one of the primary reasons for sea level rise. When water heats up, it expands (2). This is called thermal expansion, and states that warm water takes up more space than cold water (2). About half of the past century’s rise in sea level is attributable to these warmer oceans occupying more space (2). 

Another cause of sea level rise is the melting of glaciers and polar ice caps (2). These large ice formations naturally melt a little during the summer, and freeze again during the winter (2). However, due to higher temperatures caused by global warming, there have been greater-than-average summer melting as well as diminished snowfall, a key factor in balancing out the melting (2). 


Three years are shown to illustrate the model-simulated trend. A dynamic reduction of summertime sea ice is projected (August, September, October), with the rate of decrease being the greatest during the 21st century. http://www.gfdl.noaa.gov/cms-filesystem-action/user_files/kd/pdf/gfdlhighlight_vol1n1.pdf

These changes will have a significant impact on coastal ecosystems, water resources, and human settlements. There are billions of dollars invested in coastal infrastructure, and many of the world’s largest cities are located on a coastline (3). Over 150 million people live within one meter of high tide level, and 250 million people live within 5 meters (3). These people are at risk for severe storm surge and inundation of their homes and businesses. Sea level rise also contributes to coastal erosion and inundation of low-lying coastal regions, particularly during extreme weather events (3). When large storms hit land, higher sea levels mean bigger, more powerful storm surges, and these surges are capable of destroying everything in their path (2). Higher sea levels and the resulting higher storm surges could also lead to saltwater intrusion into aquifers, deltas, and estuaries, which would damage the freshwater system (3). 

UN Potential SeaLevel Rise - Bangladesh

Bangladesh, one of the world's poorest nations is also the country most vulnerable to sea-level rise. The population is already severely affected by storm surges. Catastrophic events in the past have caused damage up to 100 km inland. It is hard to imagine to what extent these catastrophes would be with accelerated sea-level rise: http://www.grida.no/publications/vg/climate/page/3086.aspx

Over the past century, the Global Mean Sea Level has risen by 4-8 inches (10-20 cm) (2). However, the rates of sea level rise around the globe are not uniform, as some regions have experienced a higher rise than other areas (4). Most scientists expect the sea levels to keep rising as the global climate is projected to rise as well (2). There are multiple predictions for the future climate, and these are determined by climate models, similar to what will be used in this exercise. 


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