Rising Sea Levels Demonstrate Climate Change Impacts Local Communities
Sea level is expected to rise significantly over the next century due to global climate change. The Intergovernmental Panel on Climate Change estimated that average global sea level would rise between 7.5 inches and 3 feet by 2100, but the predictions are very uncertain. Some scientists, in fact, have predicted that sea level rise may be much greater, up to 7 feet.
Global sea level change or "ecstatic" sea level change, is due to two causes. The first is the thermal expansion of the volume of the oceans due to warming (a kilogram of warm water takes up more space than the same mass of colder water). The second is an increase in the volume of water in the oceans due to the melting of ice on lands, such as the Greenland and the Antarctic Ice sheets. The melting of ice on the oceans, such as the northern polar ice cap has little impact on sea level since the weight of the ice already impacted sea level, and the water is already in the ocean. (Example: ice melting in your drink doesn’t overflow the glass).
Relative sea level rise, which is the relationship between the height of the ocean and the land, can vary considerably from place to place. This is because in some areas the land may be either rising or sinking relative to sea level. At high latitudes, the land surface has changed as the crust adjusts to the loss of the huge weight of the ice present on land from the ice ages. In New England, the position of the Gulf Stream also affects local sea level. Overall, sea-level rise rates in the Gulf of Maine are relatively high compared to many other regions. For example, records from Boston show that over the last century sea level rose a little more than 10 inches and rates may have increased over the last two decades (Figure).
Teaching students about sea-level rise offer an opportunity to enhance their understanding of the science of global change while providing some concrete examples of how it might impact them and their communities. Most coastal communities now have good elevation data, and students can use these data to map where sea level will be in the future. There are also on-line tools students can use to explore the implications of sea-level rise on not only their own communities but places all over the world
In addition to mapping exercises, some teachers have had their students walk from the beach to the center of town placing signs or using chalk on roads to show which areas might be underwater in 2100 (often with other community activities such as earth day). Others have gone out during times of the highest tides of the year and shared images with other communities around the Gulf of Maine (http://gulfofmaine.kingtides.net/). After gaining a better understanding of the issues, students can then explore ways in which their community might become more resilient to climate change (http://www.gulfofmaine.org/2/climate-network-homepage/ ).
High tide at the Ipswich Yacht Club during a storm.
This graph shows changes in sea level measured by NOAA at the Boston, MA tide gauge since 1920. The vertical axis is a measure of sea level relative to a value established in 1988. The blue line shows the monthly data. The red line is the average trend line over the entire time period, which equals a sea level rise rate of 0.28 cm/yr.
Dr. Anne Giblin is a senior scientist at the Ecosystems Center Marine Biological Laboratory, Woods Hole, and Massachusetts. Dr. Giblin's major research interest is cycling of elements in the environment. Current projects include an assessment of how a major sewage diversion has altered sediments in Boston Harbor and Massachusetts Bay; how increased N inputs; how hydrologic disturbances alter nitrogen cycling in estuaries; and how pathways of nitrogen cycling change with increased nitrogen inputs in arctic lakes. Anne is committed to bringing science to youth and youth people to science.