Climate Change and Sea Level Rise GEOL 1445 Oceanography / PHYS 1417 Physical Science Il South Texas College Climate Change and the Hydrosphere Earth's hydrosphere consists of different reservoirs. The largest reservoir of water is Earth's oceans, which store over 97% of Earth's water. Earth's cryosphere, consisting of ice sheets, mountain glaciers, permafrost and sea ice, is another important reservoir of water. As climate change occurs, Earth's cryosphere responds. The area covered by Earth's polar ice caps tends to grow as climate cools and diminish as climate warms. Also as climate changes, sea level tends to fall and rise. During the Last Glacial Maximum, Earth's global average temperature was approximately 4 to 6 "C colder than present, and mean sea level was 1 13 to 135 meters lower than today. The Laurentide Ice Sheet covered a substantial portion of North America. Today, anthropogenic activities are increasing the amount of COz in Earth's atmosphere, driving global warming. As global temperatures warm, melting glaciers contribute to sea level rise. In this lesson, we will explore sea level rise, contrasting the behavior of land ice and sea ice. 60 70 80 BC 70 60 50 50 Laurentide, Ice sheet 40 40 30 30 20 20 American Meteorological Society 130 120 110 100 90 80 70 Figure 1: North America During the Last Glacial Maximum Sea Level Rise As stated in the previous paragraph, Earth's mean sea level (mal) is presently rising as a result of global warming. It is projected to rise between 0.5 and 1.5 meters by the year 2100. Although this may seem like a small increase, the anticipated impacts of rising sea level are profound. Globally, much of theworld's population lives in low lying coastal areas. Studies of the impacts of climate change estimate that one meter of sea level rise will displace 145 million people, generating stresses on agricultural production, economic well-being, and social services. Therefore, understanding the physical processes which affect sea level is essential knowledge for any student of the physical sciences. Estimated impact of uniform 1 meter sea-level rise on people millions of people 120 100 Total population flooded = 145,000,000 80 60 UNEP, GLOBAL OUTLOOK FOR ICE AND SNOW 40 20 Africa Australia Europe Latin North O Asia America America Figure 2: Estimated Number of People Impacted by Sea Level Rise, credit to Gillette and Hamilton in Science Scope (201 1) Thermal Expansion of Seawater In physical science and oceanography classes, we study thermal expansion, defined as the tendency for most materials to expand as they warm. We learn that, at temperatures between 0 and 4"C, water exhibits unique behavior, contracting as it warms expanding as it cools - with important implications for aquatic life in freshwater lakes during wintertime. However, this unique behavior only applies to freshwater. Within any given temperature range, seawater expands as it warms. As global warming proceeds, Earth's oceans warm. This causes seawater to expand, occupying a larger volume, which causes mal to rise. Thermal expansion of seawater accounts for 60% of projected sea level rise by the year 2100.O American Meteorological Society 20 1.0245 g/cm3 1.0250 15 1.0255 1.0260 1.0265 10 1.0270 Temperature (C) 1.0275 1.0280 5 1.0285 1.0290 0 33.5 34.0 34.5 35.0 35.5 36.0 36.5 Salinity (psu) Figure 3: Seawater Density as a Function of Temperature and Salinity Melting Glaciers Warming temperatures cause glaciers to shrink as they melt, and glacial melt water finds its way into Earth's oceans, causing sea level to rise. Continental glaciers, also known as ice sheets, dominate the landscapes of Antarctica and Greenland. Two continental glaciers cover Antarctica, the East and West Antarctic Ice Sheets. The East Antarctic Ice Sheet is the larger of the two, accounting for two thirds of Antarctic ice. In response to a warming climate, melting of Antarctica's glaciers contributes to sea level rise. Complete melting of the East Antarctic Ice Sheet would cause mal to rise about 60 m, while complete melting of the smaller West Antarctic Ice Sheet would raise mal by 5.8 m. Fortunately, such extreme melting is unlikely within this century, although some studies suggest that the West Antarctic Ice Sheet is more vulnerable to sudden collapse than the more stable East Antarctic Ice Sheet. Antarctica's ice sheets are polar glaciers. In contrast, the Greenland Ice Sheet is a temperate glacier, and glacial dynamics suggest that temperate glaciers can melt away more rapidly than polar glaciers. The margins of the Greenland Ice Sheet are undergoing substantial thinning, contributing to sea level rise. Annually, melting of the Greenland Ice sheet raises mal by 0.13 mm. Complete melting of the Greenland Ice Sheet would cause 7.3 m of sea level rise. In contrast to ice sheets, mountain glaciers are quite small. However, mountain glaciers are an important source for regional water supplies in some locations, such as the western United States. Global warming is causing mountain glaciers to disappear, threatening the water source that many people depend upon. Runoff from melting mountain glaciers is estimated to cause 0.4 mm of annual rise in msl.Greenland NASA Visualization Figure 4: NASA Visualization of Greenland Sea Ice In the Arctic Ocean, global warming is decreasing the spatial coverage of sea ice. The area of the Arctic Ocean covered by sea ice always grows during winter and shrinks in the summer. However, examining current trends, the area covered by sea ice is becoming progressively smaller every summer. It has been estimated that the Arctic Ocean will be completely free of ice during summers by the end of the 21* Century. Melting of sea ice does not contribute to sea level rise. However, it affects climate change through important feedback mechanisms, such as the ice albedo feedback. You will investigate why melting sea ice does not contribute to rising sea level, whereas melting glaciers do contribute. Arctic sea ice minimum 9- 8 7 - Million square km 6 5 4 1980 1985 1990 1995 2000 2005 2010 Year Figure 5: Extent of Sea Ice in the Arctic Region during Summer, credit to AMS Ocean StudiesLab Activity: Sea Ice vs Land Ice Now, we will directly observe the effect of melting ice on sea level. You will use the following materials. One clear plastic glass Ice cubes Masking tape or Sharpie Marker Pour water into the glass until it is half-full, and mark the water level with a piece of masking tape (or Sharpie marker). Afterwards, place several ice cubes into the glass. Mark the new water level. Continue observing the glass until all of the ice cubes completely melt. Mark the final level of water in the glass. Figure 6: Plastic Cups with Water and Ice, credit to AMS Ocean StudiesPostlab Questions 1. For seawater with a salinity of 35 psu, what is its density at 0"C7 3"C? 6"C? Is this consistent with the concept that seawater always expands as it warms? Why or why not? 2. A friend of yours who is skeptical of climate change says that Arctic Sea Ice was growing at the end of the last decade (2007 thru 2010), suggesting that this indicates that global warming is not happening. What would you tell your friend? In climate science, why are long term trends more important than trends over shorter periods? 3. Explain why melting sea ice does not contribute to sea level rise. 4. What have you heard or read about climate change and sea level rise before taking this class? How is this similar and/or different to what you've learned in this lesson?5. The Greenland Ice Sheet is up to 3.2 km thick, and the Antarctic Ice Sheets are up to 4.8 km thick. If you walked these distances from the South Texas College campus, where would you end up? 6. Consider the impacts of projected sea level rise at some specific locations in the following regions: the Texas Gulf Coast, South Florida, the Bay of Bengal, the U.S. East Coast, the Netherlands, and the Maldives. References Battisti, D.S., Personal Communication, 2015. Gillette, B. and C. Hamilton, Flooded! An Investigation of Sea-Level Rise in a Changing Climate, Science Scope, Vol. 34, No. 7, March 2011. Moran, J.M., Ocean Studies: Introduction to Oceanography, 3d ed., American Meteorological Society, 2011. Acknowledgements This lesson evolved from the School of Ice Workshop in the Summer of 2015 funded by the U.S. Ice Drilling Program and the American Meteorological Society. Figure 7: Photograph by Mario Lopez at School of Ice