Sea level measure refers to the surface of the ocean halfway between the low and high tide. The measurement is made by use of the standardized measure of sea depth and elevations of land. Sea level across the world is not the same and, hence, the measure of sea level can be defined as the mean height of the sea. Seventy percent of the earth’s surface is covered by water masses. This, however, occurred after melting of the massive ice sheets which led to the sea levels rise by 390ft or 120m. This occurred around 18000 years ago when the average temperature was 4-7 degrees Celsius. However, since then, the global mean sea level (MSL) has been rising gradually. Previously, tide gauges were used in measuring sea levels. However, from the mid-20th century, satellites have been mostly used. To generate understanding of the history of sea levels, scientists obtain archeological information from coral reefs and salt marshes. According to the IPCC, the average rise in sea level has been 1.7mm per year, however, within the period; the highest rate was recorded between the years 1961 to 2003, where it was 1.8mm. Drastic rise within the period, as per the observation obtained from satellite altimetry, was between 1993 and 2003, which averaged 3.1mm per year (Munavvar 1989).
Causes of Rise in Sea Levels
There are various causes of rise in the sea levels, both natural and anthropogenic. The various causes result in to different regional influence. One of the main causes is the thermal expansion which results from different abilities of water to lose the heat obtained due to depth. Sea water expands when it becomes warm. However, it is possible to lose heat by the upper layers of the ocean water to the atmosphere. Heat that is contained by the water in the deep layers will be difficult to be lost. Such heat will keep the volume of the water higher than if the water was cooler. Such heats trapped in the water masses have significant influence on the sea levels.
Global temperature on the surface is also a major cause of the rise in sea levels. This is through freshwater input to the oceans after sea ice, glacier, ice caps and ice sheets melts. Glaciers are mainly found in Alaska, mountains of Europe and Asia and in the western side of the United State. When temperature is high on the surface, glacier melts at a higher rate than it gets replaced, causing to a rise in sea levels. The glacier in the US and Alaska has been shrinking at a dramatic rate in the recent past (Tarr 1998, 28-56).
The tectonic activities within the plates of the earth may also result in to a physical force that leads to changes in the sea levels. Tectonic activity may result from the human activities, such as oil and gases extractions or even natural occurrences, such as melting of glacier. These activities have no effect on the volume on water held on the seas, but rather on the relative sea levels. A good example is the Gulf of Bothnia (Sea Level Rise 2012). Over time, the massive glacier on this land has caused pressure that has led to the sinking of the land. However, in the recent past, glacier has been melting, making the region rise as the pressure beneath the glacier reduces. The sea level seems to be dropping at the rate of 11mm per year, while in essence; the sea level has been rising at the rate of 2.1mm per year (Bhambri 2009, 5-33).
From a collective perception, the two main anthropogenic causes of the rise in the sea levels are the greenhouse gas sequestration and the high mass loss when the world’s ice sheets and glaciers melt. The average sea temperature has been rising, because out of the heat that has been produced by the greenhouse gases, 10% has been held within the oceans. Within the last one decade, thermal expansion has been the cause of half of the observed rises in the sea level, as opposed to approximately quarter of the rises there before. Glacier and ice sheets from Antarctica and Greenland have had a contribution of about 1.2mm to the rise in the sea level.
Impact of Sea Level Rise
The impact of the rise in sea levels is that the low-lying coastal areas get submerged. As the trend continues, the frequency of flooding of coastal regions will rise. The repercussions of the water events, such as high tides, storm surges and surface waves will become more drastic. The loss of land and flooding is expected to affect the entire ecosystem.
Effect on Ecosystem
Different marine organisms live in different depths of the water. When their particular habitats change due to change in the sea levels, then they have to migrate or even adapt to their new position. However, various organisms’ migration may be hampered by the gradual rise in the sea levels and, hence, they may end up becoming extinct. Higher sea levels will significantly impact on function, structure and capacity inland ecosystem and, hence, impairing their ability in their ecosystem services.
Human settlements in the cost region also affect how the organisms are able to migrate to play their role in nature. A good example is the mangrove forest and coastal wetlands of Thailand and Bangladesh. Rise in the sea levels is making these features that act as buffer to tidal waves and storm surges get submerged. Ideally, the mangrove forest would re-establish at areas that experience the low tides. However, human developments such as buildings, act as a barrier to enable the re-establishment and, hence, the rise impact on the ecosystem.
Effect on HumanPopulation
Coastal regions on the whole world appear as hubs for economic activities for being endowed with a lot of resources. These include; agriculture, fisheries, tourism and aquaculture. For this reason, approximately half of the world’s population lives in the coastal region. For example, according to the study conducted in 2001, the major economic activities and 90% of Guyanas are threatened by the climate change and rise in the sea level. In Samoa, retreatment of shoreline is as much as 160ft, making peoplerelocate to higher regions.
U.S Coastal Cities
It is estimated that by 2100, approximately 9% of the land, where 180 coastal cities in the U.S., will have been submerged due to rise in the sea level. Southern Atlantic and Gulf are expected to have experienced the most severe consequences together with cities, such as Tampa, Miami, Fla, New Orleans and Virginia Beach. All these cities have more than 50000 people and, hence, the impact is estimated to have drastic effect on human settlement and economic activities (Tarr 1998, 28-56).
According to Jeremy L. Weiss, a senior scientist in the University Arizona geosciences department, sea level is likely to have risen by 1 meter by 2100 mostly resulting from temporary flooding, erosion and permanent inundation. According to the U.S. 2000 census, within 20 coastal municipalities, there lived more than 300000 people. According to Weiss, the sea level may rise to as high as 6m by 2100, causing a displacement of about a third of the coastal cities. This will include the 10% of major cities such as New York and Boston.
According to a World Bank report of 2001, the rise in sea level was 3.3mm per year at the Bay of Bengal. It was noted the threat was posed to Sundarbans, which is arguably the largest forest globally. The threat here is to the Bengal tigers and different bird species that inhabit this place. If the rise in sea level proceeds as estimated, then, more than 13-30 million people will be displaced. Additionally, the massive rice production region would be flooded. The reduction in rice produced is estimated to be as high as 30% of the current production in the whole country.
The sea level in Bangladesh is increasing twice the rate of the U.S. One of the reasons is that river Ganges and Megha that bring water from Himalayas join to form a delta that eats into the available land for Bangladesh. Though the country experiences tornadoes and cyclones, they are expected to become disastrous and common with time.
In conclusion, it is clear, as covered by this paper, that there are various causes that lead to rise in sea levels. The effects are disastrous, as noted in such country as Bangladesh. It is, therefore, imperative to address the primary causes; mainly the climate change. This is especially through control of the greenhouse gases that have resulted in to the global warming. Remarkable efforts have been made through the Greenhouse gas protocol, and it should be upon everyone to ensure the political will in its implementation.